Jimmy Kim - QUT · Jimmy Kim Principal Supervisor: Dr. Poologanathan KEERTHAN Associate Supervisor:...

DEVELOPMENT OF MODULAR BUILDING

SYSTEMS MADE OF INNOVATIVE STEEL

SECTIONS AND WALL CONFIGURATIONS

Jimmy Kim

Principal Supervisor: Dr. Poologanathan KEERTHAN

Associate Supervisor: Prof. Mahen MAHENDRAN

Submitted in fulfilment of the requirements for the degree of

Master of Philosophy (Engineering)

School of Civil Engineering and Built Environment

Faculty of Science and Engineering

Queensland University of Technology

2019

Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations i

Keywords

Case Study, Cold-Formed Steel Sections, Fire Performance, Light Gauge Steel Framed

(LSF), Modular Building Systems (MBS), Prefabrication, Rivet-Fastened Rectangular

Hollow Flange Channel Beam (Rivet-Fastened RHFCB), Stiffened Channel Sections,

Thermal Modelling.

ii Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations

Abstract

Modular building systems and the modular construction techniques are construction

technologies that show promising capabilities to deliver construction results far

superior to those of traditional construction methods. This developing technology

exhibits the potential to provide results far superior to those otherwise obtained using

traditional construction methods including time, costs and waste savings. These

savings are attributed to its systematic, controlled and integrated processes that allow

project activities to be completed simultaneously. The modular construction process

follows that individual volumetric building units (modules) are constructed off-site in

a factory setting, transported to site and then assembled together in an arrangement

that constitutes a building structure.

The modular construction method is recognized as an emerging technology with the

industry still developing and refining this technology. The full potential of the modular

construction technology has yet to be completely realised with shortcomings and

drawbacks limiting their capabilities. The examination of real-world modular

construction projects has revealed shortcomings to be: poor structural-efficient designs

of the modular building systems (strength-to-weight performance), lack of control of

construction tolerances, impractical designs resulting in increased assembly efforts

and lack of measures to address fire-resisting performance.

To address these issues, this study has been performed to further the understanding of

modular construction and propose solutions to address the several recognised

shortcomings. Modular building systems have been thoroughly examined to establish

an understanding of their complex technology. Current cold-formed steel technologies

have been reviewed, particularly the Rivet-Fastened RHFCB section which is later

introduced as an innovative design to address the shortcomings of modular building

systems.

The study provides a comprehensive execution of case studies to analyse and pinpoint

the drawbacks and shortcomings of modular construction seen in real world projects.

These case studies have also examined current developing technologies that have been

developed to address these shortcomings.

Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations iii

The development of several wall systems is presented and introduced as innovative

designs to address the shortcomings of structural efficiency and fire-resisting

protective measures. These wall systems differ between each other through their

arrangements of gypsum plasterboard layers and cavity insulation. They are then

analysed through finite element modelling to predict their fire-resisting performance.

Each wall system configuration proved to provide superior fire-resisting performance

when compared to the standard wall system. Among the systems considered,

Configuration 5 demonstrated the best performance. Configuration 5 consisted of a

discontinuous arrangement of cavity insulation and back-blocking boards on either

side of the steel studs in the form of Gypsum Plasterboard.

The innovative concepts presented in this study are then combined to present a

conceptual design proposal of a modular building system. The proposed modular

building system took the form of a corner supported module and incorporated the rivet-

fastened RHFCB as the edge beams and joists to increase the structural efficiency.

Stiffened channel sections line the walls to provide greater structural stability and a

double Gypsum Plasterboard setting is adopted in the roof and floor systems for fire-

resisting measures. Several wall systems are proposed with each highlighting their

advantages and appropriate applications. Simple connections are adopted throughout

the system to minimize assembly efforts. The proposed design then concludes with

concepts to adopt for application in multi-storey modular building systems.

In summary, this study has introduced modular building systems and the modular

construction method. This promising technology has the capability to deliver

construction results far superior to those attained through traditional construction

methods, although it is still developing and has yet to realise its full potential. The

shortcomings and drawbacks of this technology are pinpointed, and innovative ideas

and designs are introduced to address these. This study concludes that with further

investigation, the full potential of the modular construction method can be achieved.

iv Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations

Table of Contents

Keywords .................................................................................................................................. i

Abstract .................................................................................................................................... ii

Table of Contents .................................................................................................................... iv

List of Figures ......................................................................................................................... vi

List of Tables ......................................................................................................................... xiii

List of Abbreviations .............................................................................................................. xv

Statement of Original Authorship ......................................................................................... xvi

Acknowledgements .............................................................................................................. xvii

Chapter 1: Introduction .................................................................................... 19

1.1 Background .................................................................................................................. 19

1.2 Context ......................................................................................................................... 28

1.3 Aim .............................................................................................................................. 28

1.4 Significance, scope and definitions .............................................................................. 29

1.5 Thesis outline ............................................................................................................... 30

Chapter 2: Literature Review ........................................................................... 31

2.1 Introduction .................................................................................................................. 31

2.2 Cold-Formed Steel ....................................................................................................... 31

2.3 Structural Design of Cold-Formed Steel Structures ..................................................... 36

2.4 The Rivet-Fastened Rectangular Hollow Flange Channel Beam ................................. 40

2.5 Modular Building Systems ........................................................................................... 44

2.6 Findings, Summary and Implications .......................................................................... 79

Chapter 3: Case Studies..................................................................................... 85

3.1 Introduction .................................................................................................................. 85

3.2 461 Dean, New York City. ........................................................................................... 85

3.3 SOHO Apartments, Darwin ......................................................................................... 94

3.4 Octavio’s and Pascual’s Affordable Steel Concept .................................................... 100

3.5 The Verbus System .................................................................................................... 110

3.6 Double Skin Steel Panel Wall System ....................................................................... 117

3.7 VectorBloc Connection System ................................................................................. 121

3.8 Connector System for Building Modules by Verbus Systems ................................... 125

3.9 Conclusion ................................................................................................................. 130

Chapter 4: Thermal Modelling of Light Gauge Steel Framed Wall Systems

Proposed for Modular Building Systems ............................................................. 131

4.1 Introduction ................................................................................................................ 131

Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations v

4.2 Innovative LSF Wall System Configurations .............................................................133

4.3 Thermal Properties......................................................................................................136

4.4 Method of Numerical Studies .....................................................................................138

4.5 Results ........................................................................................................................140

4.6 Conclusion ..................................................................................................................146

Chapter 5: Conceptual Design of an Improved Modular Building System 147

5.1 Introduction ................................................................................................................147

5.2 Design Considerations ................................................................................................147

5.3 Design Inputs ..............................................................................................................149

5.4 Proposed Modular Building System Conceptual Design ...........................................153

5.5 Multi-Storey Configurations .......................................................................................170

5.6 Conclusion ..................................................................................................................173

Chapter 6: Conclusions ................................................................................... 174

6.1 Conclusions ................................................................................................................174

6.2 Literature Review .......................................................................................................175

6.3 Case Studies ................................................................................................................176

6.4 Thermal Modelling of Light Gauge Steel framed Wall Systems Proposed for Modular

Building Systems ........................................................................................................177

6.5 Proposed Conceptual Design ......................................................................................178

6.6 Recommendations and Future Research .....................................................................179

Bibliography ........................................................................................................... 181

vi Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations

List of Figures

Figure 1-1: A three-dimensional steel-framed modular building system being

hoisted into place (TLG Modular Building Solutions, n.d.). ....................... 20

Figure 1-2: A two-dimensional structural steel frame being erected (Reardon,

David, & Downton, 2013). ........................................................................... 20

Figure 1-3: The Nicholson of Melbourne, Australia (Archi Channel, n.d.). .............. 21

Figure 1-4: Standard cold-formed steel sections and shapes. .................................... 22

Figure 1-5: Hollow Flange Beam Profile and Dimensions (Dempsey, 1990). .......... 23

Figure 1-6: Profile of the LiteSteel Beam (Steau, 2014). ........................................... 24

Figure 1-7: The manufacturing process of the LiteSteel beam (LiteSteel

Technologies America LLC, 2006). ............................................................ 25

Figure 1-8: Applications of LiteSteel Beams (LiteSteel Technologies America

LLC, 2010) and (Building Design & Construction, n.d.). ........................... 26

Figure 1-9: Rendered images of the Rivet-Fastened RHFCB. ................................... 26

Figure 1-10: Profile of the Rivet-Fastened Rectangular Hollow Flange Channel

Beam (Steau, 2014). ..................................................................................... 27

Figure 2-1: The structural frame of this residential structure consists of cold-

formed steel members (All Steel House Frames, n.d.). ............................... 32

Figure 2-2: Cold-formed steel decking overlayed by reinforced concrete in a

composite floor system (Luke Allen, 2014). ................................................ 32

Figure 2-3: Peter Naylor's advertisement titled "Portable Iron Houses for

California" (Browning, 1995). ..................................................................... 33

Figure 2-4: The cold roll-forming process (Chicago Roll Company, n.d.). ............... 34

Figure 2-5: The press braking method (ThomasNet.com, 2012). .............................. 35

Figure 2-6: The standard I-section is composed of two flange elements and a

single web element. ...................................................................................... 36

Figure 2-7: The ‘chequer board’ wave like pattern of local buckling

deformation (Quimby, 2014). ...................................................................... 37

Figure 2-8: Shear buckling of a lipped channel section (Hancock & Pham,

2013). ........................................................................................................... 38

Figure 2-9: Distortional buckling of a channel section (Keerthan, 2010). ................. 38

Figure 2-10: Lateral distortional buckling of a channel section (Keerthan,

2010). ........................................................................................................... 38

Figure 2-11: Lateral torsional buckling of a channel section (Keerthan, 2010). ....... 39

Figure 2-12: The improved flange design of the Rivet-Fastened RHFCB. ............... 41

Figure 2-13: RHFCB1 and RHFCB2 (Poologanathan & Mahendran, 2015). ........... 42

Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations vii

Figure 2-14: Varying failure modes encountered by Steau et al. (2015).

*Modified from Steau et al. (2015).............................................................. 44

Figure 2-15: Degree of prefabrication (Smith, 2011). ............................................... 45

Figure 2-16: Nonsuch House (centre structure) as seen on London Bridge

(Landow, 2012). ........................................................................................... 46

Figure 2-17: The Balloon Frame system is composed of wooden members

(Egonarts, 2014). .......................................................................................... 47

Figure 2-18: St Mary's Catholic Church (Goodman Theatre, n.d.). ........................... 47

Figure 2-19: Advertised image of Manning's Portable Cottages (McDonald,

n.d.). ............................................................................................................. 48

Figure 2-20: Autumn 1958 cover print of the Modular Quarterly, showing the

first officially recognised Modular Assembly (Wall, 2013). ....................... 49

Figure 2-21: A full modular hospital being constructed (Steelconstruction.info,

n.d.). ............................................................................................................. 51

Figure 2-22: A modular structure comprising of a primary steel frame and

supported on a podium (ArcelorMittal et al., 2008). ................................... 52

Figure 2-23: A four-sided steel module with load-bearing walls (ArcelorMittal

et al., 2008). ................................................................................................. 53

Figure 2-24: Design details of a typical four-sided steel module (M. Lawson,

2007). ........................................................................................................... 54

Figure 2-25: An intermediate SHS post is introduced to provide support to the

open face of this module (M. Lawson, 2007). ............................................. 55

Figure 2-26: An integral corridor is implemented in the longitudinal walls of

this module (Steelconstruction.info, n.d.). ................................................... 56

Figure 2-27: An open-sided bathroom module is installed on an existing

structure (M. Lawson, 2008). ....................................................................... 56

Figure 2-28: Floorplan of apartments incorporating the partially open-sided

module – alternate modules are shaded (M. Lawson, 2007). ...................... 57

Figure 2-29: The completed apartment building of Figure 2-28 – Barling Court,

Stockwell (M. Lawson, 2007). ..................................................................... 57

Figure 2-30: A steel corner-supported module (ArcelorMittal et al., 2008). ............. 58

Figure 2-31: Structural details of a corner-supported module, end view (M.

Lawson, 2007).............................................................................................. 58

Figure 2-32: Structural details of a corner-supported module, side view (M.

Lawson, 2007).............................................................................................. 59

Figure 2-33: An open-ended module with a welded end frame (M. Lawson et

al., 2014). ..................................................................................................... 59

Figure 2-34: citizenM Hotel of Glasgow (Cheshire, 2012). ...................................... 60

Figure 2-35: Basic components of load-bearing modules. Modified from Figure

2.3 of M. Lawson et al. (2014)..................................................................... 61

viii Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations

Figure 2-36: Insulation profile of the ALHO Comfort Line by ALHO

Systembau GmbH (Rosenthal, Dörrhöfer, & Staib, 2008). ......................... 62

Figure 2-37: Conventional load-bearing side wall configuration. ............................. 63

Figure 2-38: The fin plate connection on a SHS (The Steel Construction

Institute, 2002). ............................................................................................ 65

Figure 2-39: Angle connections on the corner of steel modules (M. Lawson et

al., 2014). ..................................................................................................... 66

Figure 2-40: Workers assemble the floor base of MBSs (Vanguard Modular,

2014a). .......................................................................................................... 69

Figure 2-41: Completed metal flooring work on a MBS (Outdoor Aluminum,

n.d.). ............................................................................................................. 69

Figure 2-42: Workers assemble wall frameworks on a MBS (Outdoor

Aluminum, n.d.). .......................................................................................... 69

Figure 2-43: Workers completing the sheathing of walls on a MBS (Outdoor

Aluminum, n.d.). .......................................................................................... 69

Figure 2-44: Electrical wiring being completed on a MBS (Outdoor Aluminum,

n.d.). ............................................................................................................. 70

Figure 2-45: Inside a completed MBS (Outdoor Aluminum, n.d.). ........................... 70

Figure 2-46: MBS's wrapped, sealed and prepared for transportation to site

(Vanguard Modular, 2014b). ....................................................................... 70

Figure 2-47: Framed modular system with double skin steel wall panels (Hong

et al., 2011). .................................................................................................. 72

Figure 2-48: Double skin steel panel (Hong et al., 2011). ......................................... 72

Figure 2-49: Test arrangement used in Lawson’s and Richard’s study (R. M.

Lawson & Richards, 2009). ......................................................................... 74

Figure 2-50 General module to crane connection arrangements (M. Lawson et

al., 2014). ..................................................................................................... 77

Figure 2-51: Building joints influencing the appearance of a façade. ....................... 78

Figure 2-52: Effects due to misalignment (M. Lawson et al., 2014). ........................ 79

Figure 3-1: 461 Dean of the Pacific Park development project, New York

(Dezeen Magazine 2012). ............................................................................ 86

Figure 3-2: Structural scheme of the 461 Dean tower (Forest City Ratner

Companies, 2012). ....................................................................................... 87

Figure 3-3: Generic floorplan of 461 Dean Tower (FC Modular, n.d.). .................... 87

Figure 3-4: Structural scheme of base module chassis employed in the 461

Dean tower ................................................................................................... 88

Figure 3-5: Side view of completed a 461 Dean module chassis (Calcott, 2014). .... 89

Figure 3-6: End view of completed a 461 Dean module chassis (Calcott, 2014). ..... 89

Figure 3-7: Constructing the wall system of the modules of the 461 Dean tower

(FC Modular, 2015). .................................................................................... 89

Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations ix

Figure 3-8: The roof assembly of the base module of the 461 Dean Tower. ............. 90

Figure 3-9: The floor assembly of the base module employed in the 461 Dean

tower ............................................................................................................ 91

Figure 3-10: Misalignment of modules as seen on the 10th floor of the 461

Dean Tower (Oder, 2015). ........................................................................... 93

Figure 3-11: SOHO Apartments of Darwin, Australia. ............................................. 94

Figure 3-12: SOHO Apartments structural arrangement (Irwinconsult, 2014). ........ 95

Figure 3-13: Structural scheme of the base module chassis employed in the

SOHO Apartments structure (Irwinconsult, 2014). ..................................... 95

Figure 3-14: Side view of a completed SOHO Apartments module.

(Skyscrapercity.com, 2014). ........................................................................ 96

Figure 3-15: Module arrangement in SOHO Apartments, Darwin (Irwinconsult,

2014). ........................................................................................................... 97

Figure 3-16: Lifting of the modules forming the SOHO Apartments tower.............. 98

Figure 3-17: Octavio's and Pascual's modular tower structure (Octavio &

Pascual, 2009). ........................................................................................... 100

Figure 3-18: Octavio’s and Pascual’s Steel Module Design (Octavio & Pascual,

2009). ......................................................................................................... 101

Figure 3-19: Profiles of structural sections used in Octavio’s and Pascual’s

module design (Octavio & Pascual, 2009). ............................................... 103

Figure 3-20: Octavio's and Pascual's composite sandwich façade (Octavio &

Pascual, 2009). ........................................................................................... 104

Figure 3-21: Arrangement of concealed fasteners in Octavio's and Pascual's

composite sandwich façade (Octavio & Pascual, 2009). .......................... 104

Figure 3-22: Wall profiles of Octavio’s and Pascual’s module design (Octavio

& Pascual, 2009). ....................................................................................... 104

Figure 3-23: Roof profiles of Octavio’s and Pascual’s module design (Octavio

& Pascual, 2009). ....................................................................................... 106

Figure 3-24: Floor profiles of Octavio’s and Pascual’s module design (Octavio

& Pascual, 2009). ....................................................................................... 107

Figure 3-25: Angle connections employed in Octavio's and Pascual's module

(Octavio & Pascual, 2009). ........................................................................ 108

Figure 3-26: Overview of the module structural scheme of the Verbus System

(Verbus Systems, 2009). ............................................................................ 111

Figure 3-27: Example internal wall construction of the Verbus System

(Heather, Harding, Harding, MacDonald, & Ogden, 2007). ..................... 111

Figure 3-28: Example floor construction of the Verbus System (Heather et al.,

2007). ......................................................................................................... 113

Figure 3-29: Exploded view of corner castings (Heather et al., 2007). ................... 114

Figure 3-30: Assembled corner castings (Heather et al., 2007). .............................. 114

x Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations

Figure 3-31: Hoisting process of the Verbus System (Heather et al., 2007). ........... 115

Figure 3-32: Double skin steel panels with insulation (specimen LSP-400S)

(Hong et al., 2011). .................................................................................... 118

Figure 3-33: Double panel configuration of the double skin steel panel

(specimen LSP-400D) (Hong et al., 2011). ............................................... 118

Figure 3-34: Framed modular system MF1 (Hong et al., 2011). ............................. 119

Figure 3-35: Profile of the MCO beam (Hong et al., 2011). .................................... 119

Figure 3-36: VectorBloc Connection Systems (Vector Praxis, 2016). .................... 121

Figure 3-37: Vector Praxis’s standard VectorBloc Systems (Vector Praxis,

2015). ......................................................................................................... 122

Figure 3-38: Assembly of the VectorBloc Connection System (Bowron,

Gulliford, Churchill, Cerone, & Mallie, 2014). ......................................... 123

Figure 3-39: Assembled improved connector system (Heather, 2012). ................... 125

Figure 3-40: Exploded view of the improved connector system (Heather,

2012). ......................................................................................................... 126

Figure 3-41: A horizontal ledge incorporated in the fixing plate (Heather,

2012). ......................................................................................................... 127

Figure 3-42: A vertical plate incorporated in the fixing plate (Heather, 2012). ...... 127

Figure 3-43: Extension of the fixing plate between connector blocks (Heather,

2012). ......................................................................................................... 128

Figure 3-44: Further extension of the fixing plate between connector blocks

(Heather, 2012). ......................................................................................... 128

Figure 3-45: Lateral extrusion of the fixing plate (Heather, 2012). ......................... 128

Figure 4-1: The Grenfell Tower fire incident of June, 2017 (Dame Judith,

2018). ......................................................................................................... 131

Figure 4-2: LSF Wall System (Vardakoulias, 2015). ............................................... 132

Figure 4-3: Thermal Properties of Gypsum Plasterboard (Keerthan and

Mahendran, 2012a). ................................................................................... 137

Figure 4-4: Thermal Conductivity of Rockwool Insulation (Keerthan and

Mahendran, 2012a). ................................................................................... 138

Figure 4-5: Specific Heat of Steel in the Eurocode 3 Part 1.2 (CEN, 2005). ........... 138

Figure 4-6: Finite Element Modelling of LSF Wall Panel. ...................................... 140

Figure 4-7: Hot - Flange Time - Temperature Profiles of Conventional and

Innovative LSF Wall System Configurations at Different Critical

Temperatures. ............................................................................................. 141

Figure 4-8: Temperature Contours across Configuration 1 at Different Critical

Temperatures. ............................................................................................. 143


Temperatures. ............................................................................................. 143

Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations xi


Temperatures.............................................................................................. 144


Temperatures.............................................................................................. 145


Temperatures.............................................................................................. 145

Figure 5-1: Overview of the proposed modular system. .......................................... 153

Figure 5-2: Isometric view of the internal skeleton arrangement of the modular

system. ....................................................................................................... 154

Figure 5-3: Isometric view of the arrangement of module chassis members. ......... 156

Figure 5-4: Section view of the roof system. ........................................................... 157

Figure 5-5: Internal section view of the roof system from the outside the

module........................................................................................................ 157

Figure 5-6: Internal section view of the roof system from the inside of the

module........................................................................................................ 158

Figure 5-7: Side view of the roof system. ................................................................ 158

Figure 5-8: Section viewof the floor system. ........................................................... 159

Figure 5-9: Internal section view of the floor system from the outisde of the

module........................................................................................................ 160

Figure 5-10: Internal section view of the floor system from the inside of the

module........................................................................................................ 160

Figure 5-11: Side view of the floor system. ............................................................. 160

Figure 5-12: Isometric view of the conventional wall system frame. ...................... 162

Figure 5-13: Section view of the conventional wall system connected to the

module chasiss. .......................................................................................... 162

Figure 5-14: Overview of Wall System 2. ............................................................... 163

Figure 5-15: Detailed view of Wall System2. .......................................................... 163

Figure 5-16: Section view of Wall System 2. .......................................................... 164


Figure 5-18: Detailed view of Wall System 3. ......................................................... 165




Figure 5-22: Isometric view of the double skin steel panels within the frame of

a module. .................................................................................................... 167

Figure 5-23: Floor joists to floor edge beam interface. ............................................ 168

Figure 5-24: Roof joists to roof edge beam interface. ............................................. 168

Figure 5-25: Isometric view of the roof edge beam to corner post interface. .......... 169

xii Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations

Figure 5-26: Isometric view of the floor edge beam to corner post interface. ......... 169

Figure 5-27 Isometric view of the wall system illustrating Connection C. .............. 170

Figure 5-28: Side view of the Floor System illustrating Connection D. .................. 170

Figure 5-29: Cross bracing multi-storey configuration (left – side view, middle

– front view, right – isometric view). ......................................................... 172

Figure 5-30: Double skin steel panel multi-storey configuration (left – side

view, middle – front view, right – isometric view). ................................... 173

Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations xiii

List of Tables

Table 1-1: Yield Stress and Tensile Strength of the LiteSteel beam (OneSteel

Steel and Tube, 2010). ................................................................................. 24

Table 2-1: Various levels of building prefabrication (Smith, 2011). ......................... 45

Table 2-2: Rules of thumb for maximum dimensions of modules based on

transportation restrictions............................................................................. 60

Table 2-3: Rules of thumb for building heights of MBSs based on structural

material. ....................................................................................................... 61

Table 3-1: Summary project details of 461 Dean, New York City. ........................... 86

Table 3-2: Structural components of the base module employed the 461 Dean

tower. ........................................................................................................... 88

Table 3-3: Structural components in the wall assembly of the base module

employed in the 461 Dean tower. ................................................................ 90

Table 3-4: Structural components in the roof assembly of the base module

employed in the 461 Dean tower. ................................................................ 90

Table 3-5: Structural components in the floor assembly of the base module of

the 461 Dean tower. ..................................................................................... 91

Table 3-6: Project details of SOHO Apartments, Darwin.......................................... 94

Table 3-7: Structural components of the module chassis employed in the

SOHO Apartments structure. ....................................................................... 96

Table 3-8: Structural components of the wall system employed in SOHO

Apartments structure. ................................................................................... 97

Table 3-9: Structural components of the roof system employed in the SOHO


Table 3-10: Structural components of the floor system employed in the SOHO


Table 3-11: Octavio’s and Pascual’s Affordable Steel Concept – Project Details .. 101

Table 3-12: Structural details of Octavio’s and Pascual’s module design. .............. 102

Table 3-13: Structural sections used in Octavio’s and Pascual’s module design. ... 103

Table 3-14: Details of the interior wall profile of Octavio’s and Pascual’s

module design ............................................................................................ 105

Table 3-15: Details of the exterior wall profile of Octavio’s and Pascual’s

module design. ........................................................................................... 105

Table 3-16: Details of the interior roof profile of Octavio’s and Pascual’s

module design. ........................................................................................... 106

Table 3-17: Details of the exterior roof profile of Octavio’s and Pascual’s

module design. ........................................................................................... 106

xiv Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations

Table 3-18: Details of the interior floor profile of Octavio’s and Pascual’s

module design. ........................................................................................... 107

Table 3-19: Details of the exterior floor profile of Octavio’s and Pascual’s

module design. ........................................................................................... 107

Table 3-20: Patent details of the Verbus System. .................................................... 110

Table 3-21: Details of the wall system profile of Verbus Systems’ module

design. ........................................................................................................ 112

Table 3-22: Details of the roof system profile of Verbus Systems’ module

design. ........................................................................................................ 112

Table 3-23: Details of the floor system profile of Verbus Systems’ module

design. ........................................................................................................ 113

Table 3-24: Material properties of the steel in the double skin steel panel (Hong

et al., 2011). ................................................................................................ 118

Table 3-25: Double skin steel panel test specimen configurations (Hong et al.,

2011). ......................................................................................................... 118

Table 3-26: Section details of the MCO beam (Hong et al., 2011). ......................... 119

Table 3-27: Patent details of the VectorBloc Connection System. .......................... 122

Table 3-28: Patent details of the Connector System for Building Modules............. 125

Table 4-1: Details of the test specimen configurations. ........................................... 134

Table 4-2: Comparison of FEA Predicted Fire Resistance Ratings of

Conventional and Innovative LSF Wall Systems. ..................................... 140

Table 5-1: Details of the internal skeleton members of the module. ....................... 156

Table 5-2: Details of the roof system profile. .......................................................... 158

Table 5-3: Details of the floor system profile. ......................................................... 161

Table 5-4: Details of Wall System 1. ....................................................................... 162




Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations xv

List of Abbreviations

CFS – Cold-Formed Steel

DERW – Dual Electric Resistance Welding

ERW – Electric Resistance Welding

HFB – Hollow Flange Beam

HFS – Hollow Flange Section

HRS – Hot Rolled Steel

HSPR – Henrob Self-Pierce Riveting

LSB – LiteSteel Beam

LSF – Light Gauge Steel Frame

MBS – Modular Building System

MCM -Modular Construction Method

OSATM - OneSteel Australia Tube Mills

PFC – Parallel Flange Channel

RHFCB – Rectangular Hollow Flange Channel Beam

SHS – Square Hollow Section

QUT – Queensland University of Technology

QUT Verified Signature

Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations xvii

Acknowledgements

With great pleasure, I would like to acknowledge and thank my supervisors Dr.

Poologanathan Keerthan and Prof. Mahen Mahendran for their continual support and

instrumental guidance throughout my entire tertiary studies journey. Their wisdom and

knowledge have guided me through the ravines of higher education. Their passion for

teaching has excited my desire for lifelong continual learning. I, and many other

people, are in credit to these two remarkable leaders. I owe my deepest thanks to them.

I would also like to express my sincerest gratitude and appreciation to my fellow post-

graduate peer and dear friend, Edward (Edi). His tireless support, guidance and insight

has tremendously helped me to develop my goals and achieve them.

To my fellow peers and the Queensland University of Technology, thank you for

providing an amazing environment for my studies to thrive and grow in.

Finally, I would like to express my eternal gratitude to my family and friends for their

continual support throughout my life’s journey. There are too many to name, and I

hold them all close to my heart. I would not be who I am today if it weren’t for them;

I owe them everything.

Thank you.

19 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations

Chapter 1: Introduction

Modular construction is a developing construction technology that shows the potential

to deliver built environment structures at standards that far exceed traditional

construction methods. Possible improvements over traditional methods include: faster

construction, increased costs savings, greater sustainable capacities and further

benefits as discussed in later sections. Although modular construction technologies

have been around for a while, the advancements and developments of the technology

is relatively new and is still in its early stages. This is evident in the fact that there

cease to exist a recognised unified modular construction building code/standard.

This technology is currently developing though there are still many shortcomings that

need to be addressed before this technology can reach its full potential. This thesis will

examine these shortcomings and present innovative ideas to address them. The

innovative ideas largely stem from introducing improved cold-formed steel sections

and system configurations. Thus, this thesis will also examine the background of cold-

formed steel and improved system configurations.

This chapter introduces the research problem by presenting a background (Section 1.1)

of the relative topics introduced and then establishing the context of the research

(Section 1.2) as well as establishing the aim (Section 1.3). Succeeding this, the

significance and scope of the research (Section 1.4) is discussed followed by the

outline of the thesis layout (Section 1.5).

1.1 BACKGROUND

1.1.1 Modular Building Systems

Modular Buildings Systems (MBS) are a form of sectional structures characterized by

their segment-like construction and their unique manufacturing methods. Modular

buildings are manufactured using the Modular Construction Method (MCM). Modular

construction can be described as the prefabrication and off-site assembly of complete

volumetric, three dimensional, building units or essentially, ‘modules’. The MCM has

demonstrated capabilities to deliver construction results superior to those obtained

through traditional construction methods. The promising benefits include costs, time

and waste savings.


The benefits of MCM are attributed to its systematic and controlled process. Modular

construction differs from traditional prefabrication methods through several aspects.

One aspect is the fact that MBS arrive to site significantly more built, fabricated and

completed as three-dimensional building modules instead of bare minimal, relatively

two-dimensional structural frames and panels. Another aspect is the unique

manufacturing method that has been developed to efficiently produce MBS. Figure

1-1 shows a modular building unit being hoisted into place. Figure 1-2 shows a 2-

dimensional structural frame being erected.

Figure 1-1: A three-dimensional steel-framed modular building system being hoisted into place

(TLG Modular Building Solutions, n.d.).

Figure 1-2: A two-dimensional structural steel frame being erected (Reardon, David, &

Downton, 2013).

The manufacturing method of the MBS is similar to that of vehicle assembly line

manufacturing processes. Combined with the streamlined design of the modules, the

result is a faster delivered, more economical product with less waste and closer

tolerances. The controlled environment existing in the large manufacturing factories

also prevents undesirable defects occurring from prevalent weather conditions. These

processes along with advancing technologies have seen the MCM being implemented

into the design and construction of multi-storey, high-rise buildings, as well as plans

for towering superstructures. Figure 1-3 shows the Nicholson Social Housing Project


of Melbourne, Australia; a modular structure comprising of 197 apartments and

constructed from 341 individual modules (Hickory Group, n.d.).

Figure 1-3: The Nicholson of Melbourne, Australia (Archi Channel, n.d.).

1.1.2 Structural Steel

Structural steel represents a major market in the construction and built environment

sector. Engineers, designers and professionals alike often employ steel as structural

load-bearing members due to its high strength and predictable structural behaviour, its

adaptable form and shaping capabilities, its wide availability and economic advantages

as well as its aesthetic appeal. There are two distinct methods of producing structural

steel, each providing various advantages over the other. The methods are known as the

Hot-Rolled Method and Cold-Formed Method, and their resulting products are known

as Hot-Rolled Steel Sections (HRS Sections) and Cold-Formed Steel Sections (CFS

sections) respectively.

The hot-rolled method is the process of producing steel sections while at above the

steel’s recrystallization levels (room temperature), whereas the cold-formed method is

the process of producing steel sections while at below the steel’s recrystallization

levels. Dependent on method used, the end properties of the formed steel product can

greatly vary, offering advantages and disadvantages over one another in a given use.

HRS Sections are typical of higher strength capacities though are heavier in weight;

whereas CFS sections are relatively light weight but offer lower strength capacities.

Despite this, it is the far superior strength-to-weight ratio that distinguishes CFS

sections from their hot-rolled counterparts.

1.1.3 Cold-Formed Steel

In contrast to its heavier hot-rolled counterparts, CFS sections are recognized as a more

economical option. The light-weight of CFS sections allow it to be easily produced,


transported and installed. The relatively high-strength of the sections also provide

designers with an array of applications as structural load-bearing members. This

desirable combination of light-weight and high-strength could not have been achieved,

would it not have been for the unique manufacturing process of the steel sections.

CFS sections follow a relatively straightforward manufacturing process. At first steel

sheets are cut into predetermined widths and strips. The steel sheets are then passed

through a series of mechanical form rollers and press braking machines. These

machines apply strenuous forces to bend, shape and form desired profiles and sections

in a room temperature environment. The now formed sections are coated and painted

to specifications before being cut at required lengths. Lastly, the sections are bundled

and stored, ready for distribution.

CFS sections can be classified into two categories:

• Sheets and panels; and

• Structural members.

For an extended period, CFS structural members were only available in a small number

of standard designs, shapes and sections. This was partly due to the limiting mass-

manufacturing capabilities available. These standard structural member sections are

often simple and symmetrical designs; taking the form of a square, rectangle, circle or

C, L or Z like shape. Figure 1-4 shows several standard CFS structural sections.

Figure 1-4: Standard cold-formed steel sections and shapes.

In Australia there are three major companies who produce and supply CFS sections,

they are: Lysaght, OneSteel and Stramit. The applicable design standards for CFS

structures in the Australian and New Zealand industries are prescribed in the document

titled: “AS/NZS 4600:2018.” The document provides three established methods for


determining the structural capacities of CFS sections. These methods are: the Effective

Width Method, the Direct Strength Method and Formal Laboratory Testing.

The thin and slender geometrical profile of CFS sections is what keeps these sections

light-weight. Although, by being lean and slim these profiles are inherent of instable

structural behaviours. Thus, often it is the failure by buckling which governs the design

capacities of CFS sections.

Hollow Flange Sections

As manufacturing technologies advanced, researchers began exploring the possibility

of creating new and innovative shapes and sections with specific intentions to address

the flawed slender nature of CFS sections. Lately, a spur of innovative CFS sections

have appeared in the engineering design and research field including a series of Hollow

Flange Sections (HFS). These sections have the potential to exceed the current

capabilities of the standard CFS sections, thereby furthering the reaches of engineering

design.

HFS differ from traditional CFS sections through the inclusion of torsionally rigid

hollow flanges. The flanges are closed and sealed to the webs, establishing increased

rigidity at the extended regions of the section. Sealing the gaps between flange and

web required development of a new welding technology known as Electric Resistance

Welding (ERW). In addition, modifications to standard CFS sections producing mills

were made to accommodate the larger depth to width ratios of the HFS (Dempsey,

1990).

The first HFS to be produced were known as Hollow Flange Beams (HFB) and were

developed by Palmer Tube Mills Limited in the late 1980s (Dempsey, 1990). The HFB

consisted of a centred web met by closed triangular flanges at both ends as seen in

Figure 1-5.

Figure 1-5: Hollow Flange Beam Profile and Dimensions (Dempsey, 1990).


In comparison to standard CFS sections, the HFB was significantly stronger. However,

the awkward positioning of the flanges and their small enclosed spaces made it

difficult for member connections to be implemented and thus deemed the section

impractical. In addition, high manufacturing costs associated with the capital costs of

the new equipment, technology and the factory modifications needed to accommodate

the production of the new section, saw the discontinuance of the product in the late

1990s. As a response, several other HFS were later developed.

The LiteSteel Beam

The LiteSteel Beam (LSB) was developed to replace the HFB and was produced by

OneSteel Australian Tube Mills (OSATM) in the early 2000s (Siahaan, 2013).

OSATM developed the LSB with the intention to simplify the manufacturing

processes of the HFB and improve structural capacity. The LSB is made from

OSATM’s DuoSteel grade product. DuoSteel is a base steel with a minimum yield

stress of 𝑓𝑦 = 380𝑀𝑃𝑎 and a tensile strength of 𝑓𝑢 = 490𝑀𝑃𝑎. Cold-forming the base

steel into the LSB enhances the strength of the steel to give the following formed

properties.

Table 1-1: Yield Stress and Tensile Strength of the LiteSteel beam (OneSteel Steel and Tube,

2010).

Location Minimum Yield Stress,

𝑓𝑦 (MPa) Minimum Tensile Strength,

𝑓𝑢 (MPa)

Web 380 490

Flanges 480 500

Connection issues were prevalent in HFB due to its inclined flanges. The LSB

addresses this problem by adopting a flat web with straight flanges, allowing simple

connection in construction. Figure 1-6 shows the LSB and its profile.

Figure 1-6: Profile of the LiteSteel Beam (Steau, 2014).


The manufacturing process of LSB is similar to those of standard hollow sections, with

variation allowed for the unique geometric profile of the LSB. At first a coiled single

strip of steel is fed through a steel cutting machine; trimming and partitioning the large

sheet into specified strip widths. The steel strip is then passed through a series of

forming rolls; folding the strip into the form of a hollow flange section. The flanges

are welded to the web using a unique Dual Electric Resistance Welding (DERW)

process. To complete the production, scarfing and coating are applied followed by

sufficient cooling and drying. Figure 1-7 shows the manufacturing process of the

LiteSteel beam.

Figure 1-7: The manufacturing process of the LiteSteel beam (LiteSteel Technologies America

LLC, 2006).

Production of the LSB ceased in late 2012, when the section was recognised as

financially impractical. Siahaan (2013), associates the financial adversities of the LSB

to the higher manufacturing costs associated with the dual electric resistance welding

process, the high-priced Australian dollar and the declining Australian manufacturing

sector.

The LSB provided many applications in the Australian construction market,

particularly in residential, commercial and industrial buildings. The light weight and

strong performance of the LSB saw many applications as structural load-bearing

members. The LSB offered many advantages over other structural load-bearing

members in the application of basement beams, garage beams, ridge beams, long span


headers, floor and deck supports and mezzanine flooring (LiteSteel Technologies

America LLC, 2010). Figure 1-8 shows several example applications of the LSB.

Figure 1-8: Applications of LiteSteel Beams (LiteSteel Technologies America LLC, 2010) and

(Building Design & Construction, n.d.).

The Rivet-Fastened Rectangular Hollow Flange Channel Beam

The Rivet-Fastened Rectangular Hollow Flange Channel Beam (Rivet-Fastened

RHFCB) is the brainchild of the collaborative efforts of the researchers from the

Queensland University of Technology’s (QUT) research group; Wind and Fire

Engineering Lab. The innovation is made possible by the exclusive self-pierce riveting

technology patented by Henrob Self-Pierce Riveting (HSPR). At the time of this

proposal, the Rivet-Fastened RHFCB has yet to be patented and is only manufactured

in laboratories at the QUT and HSPR. Figure 1-9 and Figure 1-10 show the form and

profile of the Rivet-Fastened RHFCB.

Figure 1-9: Rendered images of the Rivet-Fastened RHFCB.


Figure 1-10: Profile of the Rivet-Fastened Rectangular Hollow Flange Channel Beam (Steau,

2014).

The Rivet-Fastened RHFCB was developed as an alternative to the LSB and unlike

the LSB, the Rivet-Fastened RHFCB is not formed from a single, continuous length

of uniformly thick steel sheeting. Instead, the Rivet-Fastened RHFCB comprises of

three individual and separate elements; the web and two hollow flanges. This design

feature allows the user to manipulate the combination of plate thicknesses used,

permitting optimization of behaviour and strength. For any given case, by increasing

the thickness of the web, a substantial increase in lateral distortional capacity is

achieved. In addition, the Rivet-Fastened RHFCB also has additional overlapping lip

area. This extra increase in cross-sectional area potentially provides additional strength

gains.

Several advantages are offered over the LSB using the Rivet-Fastened RHFCB. The

manufacturing process is simpler; resulting in lowered manufacturing costs. The

manufacturing process is also more flexible; allowing the ability to manipulate certain

elements of the design. In addition, the section provides sufficient room and straight

edges to allow for an array of possible connections and fixings.

Currently, ongoing work and studies are being performed to investigate the structural

behaviour of the Rivet-Fastened RHFCB under load-bearing conditions. Studies on

Rivet-Fastened RHFCB include the investigation of section moment capacity

(Siahaan, Poologanathan, & Mahendran, 2014) and web crippling capacity (Steau,

Poologanathan, & Mahendran, 2015). From what has been gathered, the section shows

promising results with expectations that it will significantly outperform traditional

CFS sections.

With the flexible design nature of modern CFS products and their inherent structural

properties, CFS products have recently gained significant popularity in the


construction industry. Engineers have begun trialling and applying the products to new

and different applications; of mention is the application of these steel sections in the

modular building industry.

1.2 CONTEXT

Although the MCM has existed for more than a century, it is still regarded as being in

its early stages of development with regards to the understanding, refinement and

progress of this construction technology. A testament to this, is the lack of a statutory

construction standard and guide to address the structural design of MBSs. The

possibilities and potential for modular construction are immense. This potential cannot

be fully realised until the shortcomings of this technology are addressed. Shortcomings

include:

• Limitations to capable efficiencies due to overbearingly heavy weight

systems of relatively low strength-to-weight ratios;

• Restrictions to achievable building heights due to insufficient lateral

strength capacities; and,

• Constraints to serviceability capacities (such as fire performance) inherent

in steel dominated systems.

This study seeks to address the shortcomings of MBSs by introducing recent

developments and advancements to incorporate in to MBSs. These advancements are

thoroughly discussed in later chapters and are summarised as follows:

• Introduction of light-weight, high-strength, innovative CFS sections;

• Inclusion of advanced, and fire rated wall systems; and,

• Incorporation of simple yet effective design arrangements.

1.3 AIM

The aim of this research is to develop an improved modular building system by

incorporating several design innovations such as:

• The Rivet-Fastened RHFCB;

• Stiffened Channel Sections

• Improved fire-rating wall systems;


• Simplified structural designs and arrangements.

This research will examine all these aspects and design innovations through a thorough

literature review. Case studies are conducted to summarise the current advances in

modular construction. Thermal finite element modelling is performed to showcase the

improved fire rating performance of several wall system configurations. The product

of this research will demonstrate the practicality of these design innovations in the

modular construction field. This thesis seeks to summarise the past, present and future

of MBSs.

1.4 SIGNIFICANCE, SCOPE AND DEFINITIONS

As examined earlier, CFS products have significant strength-to-weight ratios making

them desirable for several applications. One of such, is the application of these light-

weight sections in MBSs. In addition, the recent development of the Rivet-Fastened

RHFCB has shown promising results and improvements over traditional CFS as well

as older HFS such as:

• Expectations of greater stability and strength due to inclusion of torsionally

rigid flanges;

• Lowered manufacturing costs due to the simpler self-pierce riveting

technology patented by HSPR;

• Greater design flexibility due to the non-fixed preassembly of components;

and

• Capabilities of incorporating numerous connections due to the straight

flanges and sufficient room being provided in the web.

CFS sections have gained significant popularity in the past few years and are

continuing to do so. The market for CFS sections is large and potential exists to further

enlarge this and expand the uses of CFS sections in other markets. One of these

markets is the MBS market.

The MBS market has also seen recent and significant popularity gains, especially in

the high-rise building sector. Therefore, it is of interest that the applications of CFS

sections in MBS are explored, specifically the investigation of Rivet-Fastened

RHFCBs as load-bearing members in MBS.


This research study proposes the investigation of the application of Rivet-Fastened

Rectangular Hollow Flange Channel Beams in Modular Building Systems. It is

predicted that new MBSs with increased fire and lateral load resistance can be

developed using Rivet-Fastened RHFCB in comparison to other CFS sections. The

research seeks to further the understanding of structural and fire performances of steel

MBSs. In addition, the research will explore what structural design aspects need to be

considered to deliver a successful modular construction project.

1.5 THESIS OUTLINE

The outline and structure of this thesis follows:

Chapter 1 – Introduction: Introduce the concepts and topics of this thesis as

well as present the research problem;

Chapter 2 - Literature Review: Conduct a thorough literature review on CFS

sections including the recently developed Rivet-Fastened rectangular hollow

flange channel beam in addition to summarizing, past and present advances in

the field of MBSs;

Chapter 3 - Case Studies on Modular Building System: Investigate and

analyse existing MBSs including complete systems and individual components

(ceilings, floors, walls and connections) to establish winnings and

shortcomings;

Chapter 4 - Thermal Modelling of Innovative Modular LSF Wall System:

Investigate the fire performance of innovative modular light-gauge steel frame

wall systems using finite element modelling to recommend for incorporation

into MBSs;

Chapter 5 - Conceptual Modular Building Design: Develop and present an

improved modular building system made of Rivet-Fastened RHFCBs and

stiffened channel sections with considerably increased fire and lateral load

resistance at minimum cost using design innovations, the detailed case studies

review and thermal finite element model of the light-gauge steel frame wall.

Chapter 6 – Conclusion: Summarise the results of this thesis and make

recommendations for future works.


Chapter 2: Literature Review

2.1 INTRODUCTION

The Rivet-Fastened RHFCB is a CFS section that was introduced as a replacement for

the now production-ceased LiteSteel Beam. The Rivet-Fastened RHFCB provides vast

improvements over the LiteSteel Beam which includes aspects such as cheaper

manufacturing costs, greater structural capacity and more flexible design options.

Without question, an array of superior applications can be developed using the Rivet-

Fastened RHFCB. A particular industry which can greatly benefit from application of

the Rivet-Fastened RHFCB is the Modular Building industry. The modular building

industry distinguishes itself from other traditional construction methods by the fast

tracked, efficient and resource saving benefits it offers. The Rivet-Fastened RHFCB

can contribute to improving more over these benefits and through design of a MBS

using the Rivet-Fastened RHFCB, this thesis seeks to examine the improvements that

can be attained.

In preparation of the design, a thorough literature review of these concepts has been

undertaken and is presented in this chapter. The two main topics explored in this

section are:

• Cold-Formed Steel; and,

• Modular Building Systems.

Concluding this chapter is a summary of the findings and implications of the current

advancements in these three fields.

2.2 COLD-FORMED STEEL

2.2.1 General

CFS members represent a significant market in the steel industry. The term is used to

refer to steel products manufactured at below their recrystallization levels (room

temperature). CFS products begin their journey as thin steel sheets formed from iron

materials. The steel sheets are passed through a combination of mechanical roll

formers and press braking machines that apply strenuous forces to the steel sheets to

bend and form the desired shapes of the CFS products. It is this unique manufacturing


process that gives CFS its favourable properties such as its high strength to weight

ratio and its ease of manufacturing.

In comparison to its heavier hot-rolled steel counterparts, CFS is recognized as the

more economical option. This largely due to its superior strength-to-weight ratio which

allows more products/assemblies to be produce for a given quantity of raw material in

contrast to hot-rolled sections. In addition, manufacturing processes are more efficient

with the simpler production processes involved and lower energy consumption of not

needing to operate at high/melting point temperatures. These distinct manufacturing

techniques and technology of CFS sections allow for shapes and designs that differ

significantly from standard hot-rolled sections.

CFS products seen in the construction industry often serve as structural bearing

members in buildings, dwellings and structures alike. CFS members can be employed

as wall studs, struts, chord members, open web steel joists, space-frames, arches and

storage racks (Yu & LaBoube, 2010) and even as roofing and cladding components.

CFS products are also used as the steel decking component of composite floor systems.

Figure 2-1 below, depicts a residential structure composed of several different types

of CFS sections. Figure 2-2 below, depicts the CFS decking present in composite floor

systems.

Figure 2-1: The structural frame of this residential structure consists of cold-formed steel

members (All Steel House Frames, n.d.).

Figure 2-2: Cold-formed steel decking overlayed by reinforced concrete in a composite floor

system (Luke Allen, 2014).


2.2.2 History of Cold-Formed Steel

CFS has commonly been mislabelled as being a recent development. This can be

attributed to the fact that CFS has gained most of its popularity over the last few

decades. Though the fact is, CFS first appeared over a century ago. The first emergence

of CFS for construction use is documented to be during the 1850’s. Pioneers in both

Europe and the United States of America began trialling the material in the

construction of residential homes.

Of notable mention is Peter Naylor. Naylor was a New York State based metal roofer

that advertised the sale of “Portable Iron Houses for California”. The text of the

advertisement can be seen in Figure 2-3. The advertisement states “a house 20 x 15

can be put up in less than a day” due to the ease of construction made possible by the

interlocking grooves. Allen (2006) concluded that the iron material used in Naylor’s

offer was indeed CFS. Naylor’s offer coincided with the housing demands that

occurred during the peak 1849 California Gold Rush. As a result of the demand, it is

estimated that Naylor sold between 500-600 units according to Adam Thomas (2003).

Figure 2-3: Peter Naylor's advertisement titled "Portable Iron Houses for California"

(Browning, 1995).

Contrary to Naylor’s success, popularity of CFS products remained dormant in the

early 20th century. This can be attributed to several facts such as:

• The shortage of research on the material properties and structural behaviour

of CFS;

• The lack of design codes and standards available; and

• The absence of technology to produce economical CFS products.

This issue was soon realised and in 1938 the American Iron and Steel Institute (AISI)

appointed a committee to develop the first set of design standards for the application


of CFS (American Iron and Steel Institute, 2010). Led by Professor George Winter,

research work was conducted at Cornell university and the first Specification for the

Design of Light Gage Steel Structural Members was published in 1946, followed by

the first Design Manual in 1949 (American Iron and Steel Institute, 2010). With further

refinement and reiterations of the design guidelines along with improved

manufacturing techniques, widespread acceptance of CFS as a suitable construction

material began growing with trend continuing into the 21st century.

2.2.3 Manufacturing Method of Cold-Formed Steel Members

There are two general manufacturing methods used to produce CFS sections, both

relatively simple though with the ability to complicatedly alter the behaviour of the

steel. These methods are known as cold roll-forming and press braking.

Cold-Roll Forming

Cold roll-forming is accomplished by feeding a steel strip through a series of

consecutive, opposing rollers which continuously bend and plastically deform the strip

in incremental steps until the desired shape is attained. This process is shown in Figure

2-4. Dependent on the complexity of the section, a section can be formed with very

few roller stations or the opposite. The process can become quite complex and thus

computer software is used to assist in the design the system of rollers. The cold roll-

forming process is advantageous in its ability to quickly mass produce formed steel

sections. Although, one severe drawback of the process is the time taken to adjust and

change rolls when a different size section is required to be produced.

Figure 2-4: The cold roll-forming process (Chicago Roll Company, n.d.).


Press Braking

Press braking employs press brake machines to mimic a punch and die action, with the

punch action being the moving component and the die in the form of a fixed bed.

Figure 2-5 shows the working action of a press braking apparatus. The process begins

with the placement of a steel sheet between the punch and die. The punch is driven

down, and its resilient force bends the steel sheet to the fixed angle. This process is

repeated until the desired shape is acquired.

With the inherent stop and go nature of this process, press braking is usually employed

in situations where low volume of production is required and/or cannot be warranted

by the costs of cold roll-forming. The only major drawback of press braking is the

difficulty to produce sections exceeding 5 metres in length given the physical

constraints of the press braking machines.

Figure 2-5: The press braking method (ThomasNet.com, 2012).

2.2.4 Effects of Cold Forming

The abrupt and significant strength gains made by the steel, is specifically attributed

to the action of applying strenuous forces such as bending, rolling or punching to the

steel specimen while at room temperature. By executing the process as such, large

numbers of localised defects, cracks and fractures are created in the crystal structure

of the steel material as a result. Fundamentally, the grain sizes of the steel’s crystal

structure are reduced, and the number of grains is significantly increased, creating a

very dense, closely packed, localised environment. This change in micro-structure

prevents further slip and impedes traverse dislocations of grain boundaries thereby

effectively increasing the hardness and yield strength of the steel. This process is

known as Hall-Petch Strengthening or Grain Boundary Strengthening.


2.3 STRUCTURAL DESIGN OF COLD-FORMED STEEL STRUCTURES

2.3.1 General

CFS members are significantly thinner and lighter-weight in comparison to its hot-

rolled counterparts. Given this slender geometric profile of CFS members, a set of

different buckling modes and failures are encountered. Local buckling becomes a large

concern in with buckling stress levels at a point below the yield point. In addition, the

traditional cold-forming process often produces small geometric imperfections which

are exaggerated due to the relative thin sections that cold-formed members utilise. This

issue is not as commonly found in the traditional hot-rolled or welded members that

have larger, thicker sections. On the contrary, the local buckling of CFS also has the

potential to draw upon post-buckling reserve, providing additional strength.

Incorporating all these complex factors into simple design methods can prove quite

difficult.

2.3.2 Structural Behaviour of Cold-Formed Steel Sections

Local Buckling

Most structural steel sections can be regarded as an assembly and combination of

several individual plate elements connected to form the desired cross-sectional shape.

For example, the standard C-section, as shown in Figure 2-6, is composed of two

flange plate elements that sandwich together a single web plate element. The

compressive strength of these structural steel sections is dependent on the slenderness

ratio (width/thickness) of the individual plate elements.

Figure 2-6: The standard I-section is composed of two flange elements and a single web element.

When subjected to compressive stresses, the plate elements may buckle first before

overall buckling of the member or yielding has occurred. This event is denoted as local


buckling and the buckled plate element will display a ‘chequer board’ wave like

pattern as shown in Figure 2-7.

Figure 2-7: The ‘chequer board’ wave like pattern of local buckling deformation (Quimby,

2014).

From the onset of local buckling, the section will experience a reduction in stiffness

and hence, reduction in overall carrying capacity. Full yielding capacity will not be

achieved, and the efficiency of the section is reduced. Thus, it is desirable that local

buckling is avoided.

Hot-rolled steel sections generally consist of thick elements that provide a rigid

presence and thus carry a high local buckling capacity. CFS sections on the other hand,

are thin and slender in profile with local buckling having a greater influence on the

sections. Higher local buckling capacity can be achieved by:

• Reducing the slenderness of the plate element; in doing so, the moment of

inertia of the cross-section is increased; and/or,

• Introducing support to the longitudinal edge/s of the individual plate

elements; in doing so, the plate element will be restrained from out-of-plane

buckling. Essentially, an intersecting plate at a plate edge (the support) will

increase the relative moment of inertia of that plate element with deflection

restricted at that edge. Plate elements supported on one edge are termed as

unstiffened, whereas plate elements supported on both edges are termed as

stiffened.

Shear Buckling

Shear buckling is regarded as a form of local buckling. Keerthan (2010) regards the

occurrence of pure shear failure to be of greater chance when the member is shorter in

span. Hence, CFS sections are highly susceptible to shear buckling failure given their

slender webs and short spans. Figure 2-8 shows the stress distribution of a lipped

channel section undergoing shear buckling. As seen, the principal shear stress is


distributed in a diagonal direction. This compressive stress causes a destabilising effect

in the immediate surrounding area, resulting in buckling of the section.

Figure 2-8: Shear buckling of a lipped channel section (Hancock & Pham, 2013).

Distortional Buckling

Distortional buckling denotes the deformation of a section whereby rotation is

exhibited by the flange at the flange-web juncture, as depicted in Figure 2-9. The

distortional buckling capacity is relative to the rotational restraint at the flange-web

juncture. The onset of distortional buckling occurs when the elastic stiffness is

exceeded by geometric stiffness and flange-web juncture. Distortional buckling has

been observed to occur in both compression and flexural members although, flexural

members are more prone to distortional buckling with Schafer and Yu (2005)

attributing this to the presence of local web buckling in standard sections without web

stiffeners.

Figure 2-9: Distortional buckling of a channel section (Keerthan, 2010).

Lateral Distortional Buckling

Lateral distortional buckling denotes the deformation of a section where the web bends

transversely and the flanges exhibit zero or minimal rotation, as seen in Figure 2-10.

Figure 2-10: Lateral distortional buckling of a channel section (Keerthan, 2010).


Lateral Torsional Buckling

Torsion is described as a twisting-like action that is attributed to applying a force at a

point located a distance away from the centroid of the element of question. Many CFS

sections are mono-symmetric and thus, their shear centres do not share the same

location as the centroid. Consequently, these sections are inherent to torsional effects,

as the eccentricity of the applied force at the shear centre causes the section to twist

and therefore, lead to deformation by lateral torsional buckling as depicted in Figure

2-11. In addition, the thin profiles of CFS sections are inherent of low torsional

stiffness and adopting an open cross-section design further lowers this value. The

lateral torsional buckling capacity of a beam can be increased by adding rotational

restrains at intervals or continuously along the span of the beam.

Figure 2-11: Lateral torsional buckling of a channel section (Keerthan, 2010).

2.3.3 Design Criteria

The first known research into the structural behaviour of CFS was undertaken by

Professor G. Winter in 1939 at Cornell University. Throughout the 1940’s – 1960’s

the first design clauses were established for the correct applied use of CFS in the

industry by the American Iron and Steel Institute (AISI).

From 1979 through to 1987, Rhodes and Walker presented notable discussions and

developments on the design concepts of applying thin-walled structures to building

systems. From Rhodes’s and Walker’s overview, an array of design practices and aids

have been released.

Currently, under Australian Law, engineers, designers and professionals utilize

AS/NZS 4600 for the provisions and standards of CFS structures. AS/NZS 4600 was

first published in 1974 as AS 1538. AS 1538 heavily relied on the specifications given

in the 1968 AISI edition. AS 1538 continued to be updated throughout the years,

relying on AISI specifications. Currently, AS/NZS 4600:2018 is the latest

specification that defines the legal requirements for the design and use of CFS

structures in Australia and New Zealand. AS/NZS 4600:2018 is only applicable to


cold-formed structural members of carbon or steel material. The structural members

must be no more than 25mm thick and used only for load-carrying purposes in

buildings. AS/NZS 4600:2018 is also applicable to structures other than buildings

provided that dynamic effects are accounted for.

2.4 THE RIVET-FASTENED RECTANGULAR HOLLOW FLANGE

CHANNEL BEAM

2.4.1 General

The Rivet-Fastened RHFCB is a newly developed CFS section, proposed as an

alternative to the advanced but discontinued LSB section. The LSB was a CFS section

that was considerably stronger and more efficient than conventional CFS sections.

These qualities were recognized by those in the building and construction market with

the LSB section being thoroughly used in many applications and holding a large share

in the market. However, due to the significant manufacturing costs associated with its

welding process and along with several other factors, the section was deemed

economically unviable and discontinued. In a response to the event, the Rivet-Fastened

RHFCB was developed to address the shortcomings of the LSB.

Unlike the LSB, the Rivet-Fastened RHFCB is composed of three separate steel

elements as opposed to the single steel sheet used to form the LSB. To join the three

elements, the Rivet-Fastened RHFCB employs a rivet-fastening process. Due to this

method of assembling the section, the thicknesses of the web and flange are not fixed

to a uniform value. The thicknesses can vary between the elements; allowing for

numerous web and flange thickness combinations to meet the designer’s needs.

A determinant in the local buckling capacity of a steel section is the longitudinal

support conditions of its plate elements. Plate elements supported on only one of its

longitudinal edges (unstiffened elements) are more prone to local buckling. Plate

elements with two supported longitudinal edges (stiffened elements) are more rigid

and hence possess higher capacity to resist local buckling. Most CFS sections compose

of stiffened web elements and a pair of unstiffened flange elements. The innovative

design of the Rivet-Fastened RHFCB has addressed this shortcoming of the flanges by

providing a stiffened flange design, whereby all plate elements in the flange are now

supported along both of their respective longitudinal edges as seen in Figure 2-12. In


addition, the hollow flanges have been strategically placed away from the neutral axis,

improving the section’s efficiency as a beam member.

Figure 2-12: The improved flange design of the Rivet-Fastened RHFCB.

Being a new and recent development, the Rivet-Fastened RHFCB has had limited

studies performed on its behaviour and capacity as a structural steel member. In

addition, the section is not ready for implementation into the market due to the lack,

more so, non-existent and absence of design provisions for the section. The current

CFS design provisions are unsuitable and not directly applicable to the Rivet-Fastened

RHFCB. This is attributed to the section’s unique profile and geometry. There are

currently, ongoing studies taking place at the Queensland University of Technology

(QUT) that are investigating this section’s structural behaviour. The following

examines the structural behaviour studies of the Rivet-Fastened RHFCB that are

currently taking place at the QUT.

2.4.2 Flexural Behaviour

Siahaan et al. (2014) recently investigated the appropriateness of current design codes

for use on the Rivet-Fastened RHFCB when determining bending strength. The

investigation was completed by comparing the experimental results of a Four Point

Bending Test to those obtained by applying the Australian design code AS/NZS 4600

Cold-Formed Steel Structures.

AS/NZS 4600 prescribes three methods to predict the flexural behaviour of CFS

sections. They are: the Effective Width Method (EWM), the Direct Strength Method

(DSM) and experimental laboratory testing. Upon application of the EWM, two

conditions of CL. 3.3.2.3 were not met by the Rivet-Fastened RHFCB. Applying the

EWM yields results that are reasonably accurate for rivet spacing arrangements up to

100mm. Exceeding this value, yields results unacceptable in accuracy. The DSM was


found to accurately predict the flexural capacity of the Rivet-Fastened RHFCB, as the

method can account for the effects of the rivet spacing. From the experimental test

results, Siahaan et al. (2014) observed that for sections of the same profile, when rivet

spacing increased, a corresponding increase was seen in the reduction of the section’s

moment capacity. In conclusion, for AS/NZS 4600 to be appropriately applied on the

Rivet-Fastened RHFCB when determining bending strength, provisions must be

incorporated to account for the effects of rivet spacing on the beam.

2.4.3 Shear Behaviour

Investigation of the shear capacity and shear behaviour of the Rivet-Fastened RHFCB

has been carried out with experimental studies to develop appropriate shear design

guidelines for the section conducted by Poologanathan and Mahendran (2014). Two

variations of the Rivet-Fastened RHFCB were investigated. The first being the

RHFCB1; a three-element Rivet-Fastened RHFCB as depicted in Figure 2-13(a), and

the second being the RHFCB2; a single element Rivet-Fastened RHFCB as depicted

in Figure 2-13(b). Both Rivet-Fastened RHFCBs investigated in this study, adopted

rivet spacing of 100mm.

Figure 2-13: RHFCB1 and RHFCB2 (Poologanathan & Mahendran, 2015).

Poologanathan and Mahendran (2014) conducted a series of 19 experimental shear

tests on the RHFCB1 and compared the results to those obtained from applying the

current relative design code AS/NZS 4600. The experimental tests were limited to the

RHFCB1, as the section was relatively easier to produce than the RHFCB2.


Comparison of the experimental results and the results obtained through application of

AS/NZS 4600 found that the prescribed code was very conservative in predicting the

shear capacity of the beams. Poologanathan and Mahendran (2014) determined this

inaccuracy to be attributed to the code’s lack of provisions to account for the

significant post buckling reserves of the RHFCB1 and the effects of increased fixity at

the web-flange juncture

From the experimental tests conducted, Poologanathan and Mahendran (2014)

developed a set of shear design equations based on the Direct Strength Method’s

nominal shear capacity (𝑉𝑣). The equations are appropriately applicable to Rivet-

Fastened RHFCB with 100mm rivet spacing with current efforts currently being made

to thoroughly investigate the effects of other rivet spacing configurations.

2.4.4 Web Crippling Behaviour

A total of 52 experimental tests were recently conducted at the QUT by Steau et al.

(2015) to investigate the web crippling behaviour of the Rivet-Fastened RHFCB. Their

findings indicated that the web crippling behaviour of the Rivet-Fastened RHFCB is

slightly more complex than the traditional channel beam. This is partly due to the

advanced flange design of the Rivet-Fastened RHFCB, and the section’s design option

of allowing the designer to choose varying thicknesses and steel grades for the web

and flanges. The resultants of such factors are additional failure modes not normally

encountered in the common channel beam.

The types of failure mechanisms exhibited by the Rivet-Fastened RHFCB were either:

• Web Crippling Failure (36 tests) – the strength capacity of the web is lower

than the flanges and hence, the web reached failure first (Figure 2-14a);

• Flange Crushing Failure (4 tests) – the strength capacity of the flange is

lower than the web and hence, the flanges reach failure first (Figure 2-14b);

• Combined Web Crippling and Flange Crushing (11 tests) – the strength

capacity of the web and flanges are similar and hence both fail (Figure

2-14c); or

• Lip Failure (1 test) – absence of a rivet fastener at the absolute ends of the

member, leaves the lip more susceptible to deformation under applied loads

fail (Figure 2-14d).


Figure 2-14: Varying failure modes encountered by Steau et al. (2015). *Modified from Steau et

al. (2015).

Steau et al. (2015) compared the results of the experimental tests to those obtained

through application of the relative current design codes, AS/NZS 4600 and AISI S100.

They concluded that application of the codes on the Rivet-Fastened RHFCB resulted

in inaccurate results of varying degrees. The coefficient of variation (CV) between test

results and design code results was 0.175 and 0.315 for ETF and ITF load cases,

respectively. Steau et al. (2015) proposed two equations to address the unsuitability of

applying current design codes to the Rivet-Fastened RHFCB. The equations are only

applicable to Rivet-Fastened RHFCB with 100mm rivet spacing.

2.5 MODULAR BUILDING SYSTEMS

2.5.1 General

Several benefits are offered when using modular construction methods instead of

traditional methods to erect a building. Most of these benefits are due to manufacturing

or on-site construction improvements. The high-quality control environment of the

factories allows quick, efficient and systematic manufacturing of building components

(modules), while minimizing health and safety concerns. On site, construction and

installation are made easier with components specifically designed to be interlocking


and with less components to be installed, installation times are significantly reduced.

Furthermore, the unique process of modular construction projects allows simultaneous

construction phases to occur, reducing overall project delivery time. As explored in

this section, a thorough review of MBSs is presented along with an analysis of previous

studies performed on MBSs. This review will provide insight on how these benefits

are made possible in modular construction.

2.5.2 History of Modular Building System

The history of the modular building system follows the history of building

prefabrication, which is not straightforward and distinctly defined. This is partly due

to the unclear etymology and lack of a universally-agreed upon application of the

definition of the word “prefabrication”. Generally, a structure is considered

prefabricated when its components have been manufactured off-site and assembled on

site to form the structure. Though, through application of the definition, to what degree

of prefabrication must a structure be, to be considered prefabricated? Figure 2-15 best

illustrates this matter with Table 2-1 providing further details.

Figure 2-15: Degree of prefabrication (Smith, 2011).

Table 2-1: Various levels of building prefabrication (Smith, 2011).

Level Components Description of Technology

0 Materials Basic materials for site-intensive construction,

e.g. concrete, brickwork

1 Components Manufactured components that are used as part

of site-intensive building processes

2 Elements or planar

systems

Linear or 2D component in the form of

assemblies of structural frames and wall panels

3 Volumetric systems

3D components in the form of modules used to

create major parts of the buildings, which may

be combined with elemental systems

4 Complete Building

systems

Complete building systems, which comprise

modular components, and are essentially full

finished before delivery to the site


The author defines the modern definition of a modular system to be a structure

prefabricated off-site to the extent where a relatively volume-occupying structure

exists (Figure 2-15, far right). Modular systems are recognized as the greatest stage in

the degree of the prefabricated building spectrum. This section examines the history

of prefabricated buildings and its development to modern modular building systems.

The earliest documented record of complete prefabrication in the construction of

buildings is noted to have of occurred in the 16th century when Nonsuch House was

erected on the London Bridge. Figure 2-16 shows Nonsuch House (centre structure)

forming part of London Bridge.

Figure 2-16: Nonsuch House (centre structure) as seen on London Bridge (Landow, 2012).

Nonsuch House was a four-storey wooden structure, designed and wholly

manufactured in Holland (Picard, 2013). Nonsuch House was trial erected in Holland

in 1578 before being disassembled and shipped to London, England where it was

reassembled and completed in 1579 (Pepys, 2014). The assembly of the structure

employed a joiners’ technique, where no nails were used and only wooden pegs held

the structure together (Knight, 1841).

After the construction of Nonsuch House, more one-off prefabricated structures began

appearing. In the early 1830’s the world saw the introduction of the first mass-

produced prefabricated building system. The system was known as the Balloon Frame

system and is believed to have originated from Chicago, Illinois.

The Balloon Frame system composed of a series of long wooden studs (load-bearing

members) that ran from the sill plate to the top plate and was joined using metal nails.

Figure 2-17 shows the general layout of the Balloon Frame system.


Figure 2-17: The Balloon Frame system is composed of wooden members (Egonarts, 2014).

Marquit (2013), credits George Washington Snow as the developer of the balloon

frame system, though Bigott (2005), proposes that Snow was not the sole inventor and

that the system was not an idea but rather a build-up of “modest shifts in the practice

of many carpenters over time”. Marquit (2013) acknowledges that the first building to

be constructed using the balloon frame system was the St Mary’s Catholic Church on

Lake Street in 1833. However, Miller (1997), suggests the possibility that a Chicagoan

warehouse built in 1832 by Snow himself, was the first structure to employ the balloon

frame system. Though, circumstantial and insufficient evidence supports the rationale

that the structure was manufactured off-site and assembled on site by Snow. Figure

2-18 below, reproduces photographs taken of St Mary’s Catholic Church.

Figure 2-18: St Mary's Catholic Church (Goodman Theatre, n.d.).

Several years later on November 27, 1837, Australia saw its first instance of mass-

produced prefabricated buildings with an advertisement issued in the South Australian

Record by British carpenter Henry Manning (McDonald, n.d.). The advertisement was

titled “Manning Portable Cottage” and announced the availability for the purchase of


portable cottages built in London and shipped to Australia for erection. Figure 2-19

shows the images used in Manning’s 1837 advertisement.

Figure 2-19: Advertised image of Manning's Portable Cottages (McDonald, n.d.).

The idea and notion of the modular construction method began forming in the early

20th century when technological advances developed potential to address the demand

for quick housing production. Beginning mid-18th century, England’s industrial

revolution initiated quick spread of machined powered factory production. In 1906,

the world saw the first advertisement for the sale of mail-order, factory-made,

prefabricated structures produced by Aladdin Readi-Cut Houses (Marquit, 2013). A

better-known example, due to the company’s success and popularity, was Sears

Roebuck & Co., whom advertised their prefabricated building products throughout

1908–1940. During this period, Sears Roebuck & Co. is believed to have sold over

500,000 prefabricated homes (Sunbelt Modular INC., 2014).

When Henry Ford introduced the standardised assembly line, he sprouted an upheaval

of manufacturing technologies and capabilities. Dubbed Fordism, the notion is

recognised by economists to have revolutionised industrial mass production. Pioneers

recognised the possibilities of implementing assembly line production techniques in

the manufacturing of prefabricated structures and when transportation technology was

capable of transporting large volume-occupying goods, the modern modular building

industry was born.

The Modular Home Building Council, part of the National Association of Home

Builders (NAHB) of the United States, recognizes the formal birth year of the Modular

Construction Method to be 1958, when a home manufacturer produced a two-section

home conforming to applicable building codes (n.d.). Figure 2-20 reproduces the cover

of the Modular Quarterly, showing the first officially recognised modular assembly.


Figure 2-20: Autumn 1958 cover print of the Modular Quarterly, showing the first officially

recognised Modular Assembly (Wall, 2013).

Since the formal recognised birth year, modular buildings have slowly gained

popularity with introduction into other areas of building construction. Modular

systems are now incorporated in many multi-storey buildings and high-rise buildings.

In addition, there are developing plans for super structures utilising modular methods.

2.5.3 Materials Forming Modular Building Systems

The possible architectural arrangements of a MBS is governed by its structural form

and structural performance which is dependent on the materials selected for its load

bearing elements. The structural form of MBSs can be assembled from almost any

material and with modern technology it is not uncommon to find prefabricated

structures comprising of composites made of more than one material. Even with the

possibilities offered by modern technology, the wider construction industry has always

preferred traditional materials; namely concrete, steel and timber. These materials

offer an established and extensive history, with thorough research and information

detailing their behaviours. Skilled labour involving the use of these materials is widely

available and their manufacturing methods have been well refined to allow economical

production. The following section elaborates on the three most common construction

materials seen in MBSs.

Concrete

In the early modern era of the MBS, precast concrete systems were believed to be the

answer to fast construction needs, especially in the 1960s (Smith, 2011). However,

concrete systems are quite heavy and required the use of heavy-duty crane and


transport systems; resulting in high installation costs especially for smaller projects

such as residential and light commercial structures. Modular concrete construction is

preferred in larger projects, often in applications where high levels of security are

needed such as prisons, hotels, financial institutions and alike. Concrete performs very

well in mitigating vibrations and as such, they are often also employed in applications

where vibration sensitive equipment exists such as hospitals, laboratories and

factories.

Timber

Timber is a widely available material often employed in modular construction for its

natural aesthetic appeal and sustainable production. Timber modules are lightweight

and are easily manufactured. However, due to its lower structural performance

capabilities and inherently low fire rating, timber modular construction is best suited

to smaller applications such as residential buildings. Timber can competently perform

in structures up to three stories, any further and a robust, advanced, structural frame

must be implemented. In turn, this affects its price point and economy (Smith, 2011).

Steel

Currently, steel is the preferred material in modular construction for most building

heights and applications due to its all-round performance in both structural and

economical criterion. Mass-produced, thin-walled steel members provide sufficient

strength in low to medium height structures, whereas thicker steel members are

introduced in taller buildings when greater structural performance in load bearing and

seismic conditions are required. In comparison to concrete and wood, steel has greater

precision of manufacturing lending way to more accurate performance predictions.

Steel modular assemblies are relatively light weight and provide sufficient rigidity for

economical transport and placement without collapsing.

2.5.4 Types of Steel Modular Building Systems

According to ArcelorMittal et al. (2008), there are three generic structural forms of

MBS:

1. Fully modular construction using load-bearing modules;

2. Modules supported by a separate steel structure or bracing system; and

3. Non-load-bearing ‘pods’ for bathrooms etc.


Non-load-bearing pods are not structural load-bearing systems and do not pertain to

the discussion of structural forms of MBS in this section and hence herein will not be

discussed. The floor layout of modular buildings often follows a ‘systematic style’

with little variation dependent on intended function and architectural needs.

Systematic layouts reduce the difficulty in design, construction and assembly co-

ordination.

Fully Modular Construction

In fully modular construction, the overall structural stability of the MBS is the

summation of the structural capacities of the individual modules, without structural

support from any other structural elements such as frames, core walls or podiums.

Simply, fully modular construction systems are stacked assemblies of individual

modules capable of supporting their own loads and of those above. Modules in this

system are joined together through a series of connections. Figure 2-21 shows a fully

modular building being constructed.

Figure 2-21: A full modular hospital being constructed (Steelconstruction.info, n.d.).

Fully modular construction is suitable for buildings of low-medium height. Their

construction speed is superior to other forms of modular construction given the need

to not assemble and construct other structural elements such as steel frames, podiums

or core walls while on site. However, open plan space is restricted to the dimensions

of the individual modules.

Steel Frames Modular Construction

Steel Frames Modular construction denotes modular buildings which consist of a

primary and central steel frame encompassing individual modules. This type of

modular construction is often selected when large open plan space is required. The

steel frame provides the structural support to incorporate large open spaces as well as


provide additional overall stability of the structure. ArcelorMittal et al. (2008),

describes three forms of Steel Framed Modular Construction systems:

1. Modules supported on a steel podium, in which the locations of the columns

in the podium are aligned with multiples of the module dimensions, Figure

2-22.

2. Modules with fully or partially open sides supported by a steel framework

at entry floor level.

3. Modules that are stabilised by a braced steel or concrete core.

Figure 2-22: A modular structure comprising of a primary steel frame and supported on a

podium (ArcelorMittal et al., 2008).

Modular systems falling under this category are unbounded in building height. The

supporting central frame or core wall allows designers to engineer very high structures.

Larger open plan spaces are also achievable and in addition, podiums may function as

commercial spaces or car parks.

2.5.5 Types of Steel Modules

The individual modules of a modular building system determine how the system

structurally behaves as a whole system. Through combination of various module

forms, the designer can create a multipurpose building with small enclosed spaces or

large open floor plans. Selection of modules can also affect which architectural

features, building skins and facades are possible. There are four basic forms of load-

supporting modules, they are:

1. Four-sided modules;

2. Partially open-sided modules;

3. Corner-supported modules; and

4. Open-ended modules.


Four-Sided Modules

Four-sided modules, also known as continuously supported modules, are the most

common and most basic form of modules available. The four-sided module is a closed

volumetric unit composed of 2D panels. Beginning with a floor cassette, four walls are

erected, and the system is sealed with the addition of the ceiling assembly. Perforations

such as windows and doors can be incorporated, and the external dimensions of the

system are often dictated by transportation limits. Typically, four-sided modules are

4m wide with a length spanning 6-10m. Figure 2-23 shows a common four-sided

module design.

Figure 2-23: A four-sided steel module with load-bearing walls (ArcelorMittal et al., 2008).

Four-sided modules transfer their vertical loads directly through the continuous run of

walls encompassing the module. These load-bearing walls are assembled from a series

of intermediately spaced steel sections often in the form of 65-100mm deep channel

sections. The maximum height of the building is dependent on the compression

capacity of these sections and the bracing characteristics of the modules. For fully-

modular construction using four-sided modules, buildings can reach 6-10 stories

provided adequate bracing is achieved.

Corner columns, usually of larger profiles, form the end columns of the walls. In

addition to providing compression capacity, the larger corner columns often serve as

lifting points and attachments for other structural components such as balconies.

Additional steel angles can be introduced in the recessed corners of the modules for

improved stability as shown in Figure 2-24. Edge beams surround the ceiling assembly

and floor cassette of the module. Floor joists are usually 150-200mm deep channel

sections and the combined floor and ceiling depth is in the vicinity of 300-450mm

deep. Module-to-module connections are completed on site using plates and bolted

connections.


Figure 2-24: Design details of a typical four-sided steel module (M. Lawson, 2007).

Stability of the system can be established by implementing cross-bracing in the walls,

by diaphragm action of sheathing boards, by an entirely separate bracing system or by

a combination these systems. Suitability of the implemented stability measures is

dependent on the geometric form of the structure. For:

• Low rise buildings – sufficient bracing can be achieved with in-plane

bracing measures such as cross-bracing systems or diaphragm action of

board materials. Module-to-module connections will assure effective

transfer of wind action to the group of modules.

• Buildings of 6-10 stories – an access core can serve as the primary vertical

bracing system with horizontal bracing measures implemented or through

diaphragm action in the corridor floor between modules.

• Taller buildings – a podium constructed of concrete or steel is recommended

to provide a stable platform for the modules to be stacked on. In addition,

inclusion of concrete or steel cores are recommended.

As mentioned earlier, four-sided modules are the most basic form of modules available

and hence can serve in a variety of applications. It is common to implement this form


of module in buildings with cellular layouts such as hotels, student residences,

residential buildings, and key worker accommodation.

Partially Open-Sided Modules

For greater open space design capabilities, four-sided modules can be designed with

partially open sides. Structurally, the system is made possible through the introduction

of stiff, continuous, edge beams, corner posts and intermediate posts if necessary. The

partially open-sided module allows several design features to be implemented. The

manipulation of open space is more flexible and easier, with introduction of corridors,

balconies and future extensions possible. Combining the open faces of these modules

allow for wider, open, interior space to be created.

The maximum width of the opening is restricted by the structural performance of the

edge beam, namely stiffness and bending resistance. The edge beam encompasses the

floor cassette and can also be introduce in the ceiling assembly if required. The

maximum height of the building is controlled by the compression capacity of the

corner or internal posts. Structures of 6-8 stories are possible with partially open-sided

modules.

Smaller intermediate posts are introduced to provide support and additional stiffening

to the edge beams. These posts usually take the form of Square Hollow Sections (SHS).

Figure 2-25 illustrates the use of an intermediate post in a partially open-sided module.

Figure 2-25: An intermediate SHS post is introduced to provide support to the open face of this

module (M. Lawson, 2007).

The stability of these modules is dictated by their partially open sides. Often, additional

temporary stiffening is required during transport and installation of the partially open-

sided module. Insufficient shear resistance is also a common problem and can be

addressed through the introduction of a separate bracing system.


Integral corridors can be incorporated by employing partially-opened faces and are

often seen in larger and longer modules, as shown in Figure 2-26. The built-in corridor

helps to avoid the weather tightness problems that occur in creating corridors by

extending the ceiling in a void of space, thereby speeding up construction rates.

Figure 2-26: An integral corridor is implemented in the longitudinal walls of this module

(Steelconstruction.info, n.d.).

Introduction of rigid corner posts and internal posts allow balconies and extending

structures to be implemented. Partially open-sided modules may also serve as a means

of renovation to existing structures. Additional building space can be achieved by

attaching partially open-sided modules to pre-existing structures. These additional

fixtures are often load bearing with stabilisation achieved by connection to the existing

structure. Figure 2-27 shows open-sided bathroom modules being attached to an

existing building.

Figure 2-27: An open-sided bathroom module is installed on an existing structure (M. Lawson,

2008).

Partially open-sided modules are usually integrated in apartments, hotels with

corridors, student residences, communal areas and worker accommodation. The floor

layout of an apartment building (called Barling Court, Stockwell) incorporating

partially open-sided modules is shown in Figure 2-28. The erection of the modules

took four days and the building was completed in two weeks (Mike Kirk Consulting

Ltd., n.d.). The constructed and completed apartment building is shown in Figure 2-29.


Figure 2-28: Floorplan of apartments incorporating the partially open-sided module – alternate

modules are shaded (M. Lawson, 2007).

Figure 2-29: The completed apartment building of Figure 2-28 – Barling Court, Stockwell (M.

Lawson, 2007).

Corner-Supported Modules

Corner-supported modules are essentially fully open-sided modules, in other words,

all four walls have been removed. Removing all walls allows for greater open space to

be achieved, though the downfall is the severe decrease in the overall stabilisation of

the module. The width of corner-supported modules is usually between 3-3.6m and

rooms of 6-12m width can be created by combining these modules together. These

large open spaces are often required in places of mass assembly such as schools and

hospitals. Figure 2-30 shows a steel corner-supported module.


Figure 2-30: A steel corner-supported module (ArcelorMittal et al., 2008).

Corner-supported modules direct all their vertical loads through the corner posts of the

module. Edge beams surround the floor cassette to stabilise the module. In turn, both

types of members are often larger and thicker in profile to provide sufficient capacity.

Sometimes, intermediate load supporting members are introduced between the corner

posts to reduce the span of the edge beams or for stable transportation requirements

(M. Lawson, Ogden, & Goodier, 2014).

The corner posts of this module are usually in the form of Square Hollow Sections

(SHS) in common profiles of 70x70 to 100x100. If bracing is adequate, these corner

post profiles can provide sufficient compression resistance for buildings up to 10

stories tall. The edge beams often take the form of heavy CFS sections or HRS sections

such as the Parallel Flange Channel (PFC) section. Dependent on the span of the

module (usually 5-8m), the edge beams are generally between 300-450mm deep. The

combined depth of the floor and ceiling edge beams can be as high as 600-800mm.

Figure 2-31 and Figure 2-32 shows typical structural details of a corner-supported

module.

Figure 2-31: Structural details of a corner-supported module, end view (M. Lawson, 2007).


Figure 2-32: Structural details of a corner-supported module, side view (M. Lawson, 2007).

Corner-supported modules are prone to stability issues when grouped together due to

their weak bending resistance at the beam to post connections. On their own, these

modules are only stable for 1-2 stories, thus additional bracing must be employed. To

effectively disperse in-plane forces to all modules, suitable connections are to be

adopted. These connections usually take the form of end plates and hollo-bolts at the

corners of the modules. Fin plate connections are used to provide the nominal bending

resistance. Though even with these measures, additional bracing is often still required

in the structure. Thus, core lifts, core stairs or core walls are usually implemented.

Open-Ended Modules

Open-ended modules are four-sided modules without the inclusion of end walls in their

structural frame. Instead, a strong, rigid and often welded, steel end frame is

incorporated at the ends of the module to provide the bracing, stabilisation and to

support the load that the end wall would have provided. Figure 2-33 shows an open-

ended module with a welded end frame . This configuration allows the designer to

combine modules along their length and allows for full-height glazed façades.

Figure 2-33: An open-ended module with a welded end frame (M. Lawson et al., 2014).


The end frame usually consists of Rectangular Hollow Sections (RHS) welded or

rigidly connected together. The rigidity of the end frame determines the overall

stability of open-ended modules. If insufficient, stability can be improved by

incorporating a steel “exo-skeleton” system in the building. This form of modular

construction is achievable up to six stories. The overall floor depth of open-ended

modules is generally 450mm. Module-to-module connections take the form of plates

and bolts. The end frame allows full width cantilever balconies or walkways to be

attached at the ends of the modules.

In Glasgow of Scotland, citizenM constructed a 198 room hotel in the form of modular

building system. The building incorporates open-ended modules with full-height

glazing that serves as architectural features and windows as seen in Figure 2-34.

Figure 2-34: citizenM Hotel of Glasgow (Cheshire, 2012).

Dimensions of Modular Building System Modules

The dimensions of modules are dictated by several factors encompassing the project.

Though usually, the dominating factor are the requirements determined by

transportation restrictions. Local authorities enforce restrictions on the maximum

allowable dimensions and weight of transported goods as to avoid damaging transport

infrastructure and prevent the occurrence of traffic-related accidents. Specific

restrictions vary with location. General rules of thumb, detailed by Smith (2011), are

presented in Table 2-2 and Table 2-3.

Table 2-2: Rules of thumb for maximum dimensions of modules based on transportation

restrictions.

Dimension Description Common Maximum (ft.) Oversize Maximum (ft.)

Module Width 13 16

Module Length 52 60

Module Height 12 12


Table 2-3: Rules of thumb for building heights of MBSs based on structural material.

Modular Material Building Height (stories)

Wood 1 to 3

Steel 5 to 12

Steel and Precast Specialized 12 to 20+

Structural Components of Modular Building Modules

The type, quantity and configuration of individual structural members used to form the

modules of MBS are dependent on the structural form of the building system. M.

Lawson et al. (2014) details load-bearing modules to be comprised of six basic

components, these components are:

1. Ceilings;

2. Corner posts;

3. Edge Beams;

4. Floors;

5. Load-bearing side walls; and

6. Non-load-bearing end walls (or side walls if edge beams are used).

Figure 2-35 shows the six basic components of load-bearing modules.

Figure 2-35: Basic components of load-bearing modules. Modified from Figure 2.3 of M.

Lawson et al. (2014).

Standard cladding is used to form the enclosing envelope, usually in the form of

galvanised steel sheets. Within the enclosed space, insulation is often installed to

provide fire protection, improve acoustic performance, and enhance thermal control.

The insulation profile of the ALHO Comfort Line, a modular building system

developed by ALHO Systembau GmbH, is shown in Figure 2-36.


Figure 2-36: Insulation profile of the ALHO Comfort Line by ALHO Systembau GmbH

(Rosenthal, Dörrhöfer, & Staib, 2008).

Structural Design of Modular Units

In Australia, steel MBS are classified as steel structures and their behaviour is that of

frame structures. Therefore, Australian MBS can be designed using the prescribed

standards AS 4600 (for hot-rolled steel components) or AS/NZS 4600 (for CFS

components). When designing the modules, M. Lawson et al. (2014), recommend that

the designer consider other issues of structural performance, such as:

• Diaphragm action for transfer of in-plane forces due to wind actions and

notional horizontal forces.

• Structural integrity or robustness to accidental actions, which are generally

resisted by tying forces developed at connections.

• Fire resistance, which required that the structural members are fire protected

and that fire does not spread from one module to another.

The type of connections used to join the components depend on the geometric profile

of the members, their positioning, nature and magnitude of the acting loads, available

equipment, fabrication and erection considerations, and costs involved. Common steel

connections include:

• Splices (cover plate connections);

• Gusset plate connections;

• Framed connections where only webs are connected; and

• Moment connections where both flange and webs are connected.


Load-Bearing Walls

Load-bearing walls in steel modules are primarily subjected to vertical loading applied

from the weight of the modules above. Commonly, CFS sections are employed as the

vertical and horizontal structural members forming the load-bearing wall. In Australia

these sections frequently take the form of C sections that are 100mm deep and 1-3mm

thick with a steel strength of G300 (300MPa yield stress). Conventional design

configurations include spacing the vertical C sections at 400mm or 600mm centres and

in the case of heavier loadings, C sections can be paired together. Tracks (horizontal

members) encompass the vertical C sections at their ends, creating a load path for

vertical loads to be transferred between the modules above and below. Sheathing and

plasterboard are employed to enclose the structural frame of the wall. With effective

connection, the sheathing and plasterboards can prevent buckling in the plane of the

wall and lateral torsional buckling of the structural members. The void space between

structural member and sheathing is filled with insulating materials to improve fire

ratings, improve acoustic performance and mitigate vibration. Figure 2-37 presents the

conventional load-bearing side wall configuration.

Figure 2-37: Conventional load-bearing side wall configuration.

Floors

The structural role of the floor is to support the imposed dead and live loads applied

directly to them. The design of the floor is usually governed by the deflection and

vibration limits. Due consideration of the flexural behaviour of the floor is required

during phases where the floor is to be hoisted i.e. during manufacturing and installation

phases.


Generally, C sections of 150 – 200mm depth and 1.2 – 1.5mm thickness are employed

at intervals of 400mm. The 400mm spacing interval is concurrent and compatible with

most floorboard profiles. Adding of floorboards can prevent lateral-torsional buckling

and should be considered.

Ceilings

Ceiling configurations compose of a set of ceiling joists that are sandwiched between

sheathing and ceiling plasterboards. The structural role of the ceiling is to support its

self-weight and loads applied during installation and construction including indirect

flexural response when hoisting the ceiling and trafficable loads. Lawson (2008),

proposes that this temporary construction load is taken as a minimum of 1kN/m2.

Generally, the governing design factors of ceilings are the deflection and vibration

limits. Designers should consider choosing similar joists depths and profiles for both

ceiling and floor joists; in doing so, the manufacturer will be able to use the same

production system when fabricating these elements.

Edge Beams

Spanning between corner posts, edge beams are provided at ceiling and floor heights.

Their structural role is to effectively transfer half the width loading of the floor or

ceiling to the load-bearing wall below. Similar to floor and ceiling designs, the design

of the edge beam is usually governed by deflection or vibration requirements. M.

Lawson et al. (2014) recommends that the deflection ratio (span:section) of the edge

beam should fall between 18 – 24 for acceptable serviceability performance. To meet

these performance criteria, PFCs are often selected for the edge beam.

Corner Posts

Corner posts are provided in modules to resist the vertical compressive loading. For

partially and fully open-sided modules (corner supported modules), the corner posts

act as the primary (and only) vertical load resisting element. For four-sided and open-

ended modules, the corner posts acts as the secondary vertical load resisting element

in which it assists the load bearing walls in withstanding the compressive loading.

Generally, SHS of 100 or 150mm width are adopted as the corner posts. The geometric

shape of the SHS is favourable in addition to its compressive strength. Connections

between modules are often located on the corner posts. Adjacent walls are understood

to provide lateral restraint for the corner posts, though this is dependent on the profile

and stiffness of the wall i.e. highly perforated walls may not provide sufficient lateral


restraint. Due consideration of the eccentricity effects is required when designing for

combined bending and axial loading in addition to biaxial bending effects. M. Lawson

et al. (2014) recommend the eccentricity of the moment is taken as 12 mm and thus,

the total eccentricity, e (in mm), is given by:

𝑒 = 12 +𝑏

𝑛

Where: 𝑏 = width of the corner posts and 𝑛 = the number of storeys. A minimum total

eccentricity of 𝑒 = 30mm is recommended by M. Lawson et al. (2014).

Connections

The overall structural stability of a modular structure is heavily influenced by the

behaviour of the individual module-to-module connections. In addition to providing

adequate structural performance, connections need to be easily accessible and

installed. This following will examine common connection systems.

There are two common connection systems employed in most modular buildings; they

are the Fin Plate Connection and the Angle Connection; both dependent on the section

employed as the corner posts.

Fin plate connections are protruding steel plates, welded to the face of the supporting

member and with holes for bolting connection to the supported member. They are often

reserved for when SHS are employed as the corner posts of a module. Figure 2-38

shows the fin plate connection employed on a SHS (supporting member) to connect

several I-beams (supported member). The fin plate connection is designed to resist

bending moments between edge beams and corner posts.

Figure 2-38: The fin plate connection on a SHS (The Steel Construction Institute, 2002).


Angle connections are employed when angle sections are employed as the corner posts

of a module. Often, the angle section corner post will consist of welded nuts that allow

bolting to supported members. Bolting can be made directly onto the supported

member or by employing a connector plate. Figure 2-39 shows an angle connection

where a connector plate (steel framing angle) is employed to connect to supported

members.

Figure 2-39: Angle connections on the corner of steel modules (M. Lawson et al., 2014).

2.5.6 Manufacturing

Modular construction derives most of its benefits from its unique manufacturing

process and hence, the manufacturing details that follow are vital in the success of a

modular construction project. Manufacturing conditions vary and are dependent on

project needs, location and availability of resources. Most manufacturers produce

modules through one of two or a combination of factory production arrangements

called Static Production and Linear Production. These production methods and the

general manufacturing process of MBS are presented in this section.

Static Production

Static production describes the manufacturing process of assembling a module in a

fixed or stationary position from beginning to end i.e. a static position. For the duration

of the assembly, the module remains fixed in place while materials, equipment, tools

and personnel are brought to the module. In some cases, components such as wall

frames, ceiling and floor assemblies are often constructed elsewhere and brought to

the module.


Multiple components of the module can be constructed simultaneously and the rate of

production using this manufacturing process is dependent on the availability of

personnel for specialist tasks. Hence, production may be slow but on the other hand

the critical path is not limited to the completion of any one task. Typically, a large

factory can have 30 modules being built simultaneously with a completion time of 3-

7 days per module (M. Lawson et al., 2014)

Linear Production

Linear production describes the manufacturing process of assembling modules through

utilisation of a series of assembly stations. The process is sequential and follows the

principles of vehicle assembly lines. In this manufacturing process, modules are either

built on fixed rails and conveyed between stations or built on trolleys and moved

between stations. Each station has a certain set of tasks to complete in the production

of the module. Stations consist of dedicated teams, tools and equipment, specifically

prescribed for the set of tasks that needs to be completed at that particular station.

The difference between linear and static production is that modules are moved between

dedicated stations rather than the production teams having to move from module-to-

module. The main advantage that linear production offers is the faster production rates;

made possible by employing automated machines to assist in the assembly of modules.

These machines can perform with great efficiency and high accuracy. Though there

are several downfalls to employing automated machines. Primarily, these are the

capital costs of purchasing these machines and the initial setup and start up times of

the machines.

It is critical that thorough consideration of time spent at each station is made when

planning and designing the production line. In doing so, a steady production pace can

be achieved with minimization of bottlenecks and production halts. The design of

modules should also consider the sequential nature of the line. Any design changes

made late in the project’s cycle can cause disruption to the manufacturing process, as

machines are updated to reflect the changes.

Manufacturing Process of Steel Modular Building System Modules

The manufacturing process of MBSs is similar to that of automobiles, that is to say,

they both are constructed on assembly lines. To achieve the potential economic

savings, some degree of standardised manufacturing must be completed. The advance


machinery of the factory will allow repetitive processes to be completed in efficient

manners, where the potential of manufacturing savings is greatest.

Factory productions of modular systems allow the modules to stay clear from

undesirable weather conditions and be contained in controlled environments. The

controlled environment minimizes exposure to safety hazards. These factories are

typically equipped with overhead cranes and rollers to assist with transporting modules

and bulk materials. Special machinery and equipment unsuitable for use on site are

present in the factory environment allowing the factory to yield better and more

accurate products. Established factories can construct and assembling all aspects of

MBSs including mechanical fittings, painting, finishes and plumbing. Most of the

manufacturing processes involved can be completed simultaneously while other work

occurs, further reducing manufacturing times.

The manufacturing process of MBSs all follow a similar process, though with minor

variations dependent on manufacturer capabilities and the details of the output product

such as geometry and finishes. The general manufacturing process follows:

1. Floor base structure assembled and sheathed.

2. Wall framework constructed and connected to floor base.

3. Flooring completed, including all tiling, carpeting and installation of other

floor elements.

4. Wall sheathing and vapour membranes installed.

5. Plumbing, electrical installation and other services are completed.

6. Roof frame built and attached to modular unit.

7. Roof insulation, cladding and roofing installed.

8. Windows fitted.

9. Interior and exterior finished installed.

10. Modules wrapped, sealed and prepared for transportation to site.

The following figures (Figure 2-40 - Figure 2-46) show the construction sequence of

a typical modular building system in order of occurrence.


Figure 2-40: Workers assemble the floor base of MBSs (Vanguard Modular, 2014a).

Figure 2-41: Completed metal flooring work on a MBS (Outdoor Aluminum, n.d.).

Figure 2-42: Workers assemble wall frameworks on a MBS (Outdoor Aluminum, n.d.).

Figure 2-43: Workers completing the sheathing of walls on a MBS (Outdoor Aluminum, n.d.).


Figure 2-44: Electrical wiring being completed on a MBS (Outdoor Aluminum, n.d.).

Figure 2-45: Inside a completed MBS (Outdoor Aluminum, n.d.).

Figure 2-46: MBS's wrapped, sealed and prepared for transportation to site (Vanguard

Modular, 2014b).

2.5.7 Modular Building Systems in Australia

The MBS industry in Australia is relatively small in comparison to other countries.

However, there has been recent and significant growth in the sector with several large

MBS projects having been completed recently or in the process of being completed. A

large majority of these MBS projects were completed to support the growth and need

for accommodation in rural and mining towns. In 2009, Ausco Modular was tasked to

deliver a 1200 bed village and facilities project at BHP’s Spinifex Village project in

Yandi of Western Australia (Ausco Modular, 2009). Melbourne has also seen several


large MBS projects been completed, with most cases to address housing needs in

heavily dense urban locations.

To date, there yet to exists a modular building system specific statutory publication or

standard document to address the structural design of MBSs in Australia. However,

there are current works to develop a code to be applicable in the next few years.

Leading the development of the code is the Australasian Modular Construction Codes

Board. The committee comprises of researchers from Monash and Swinburne

Universities, Engineering Innovations Group, Arup, Robert Bird Group, Felicetti,

Hickory Building Systems, ML Design, Australian Steel Institute, Master Builders

Association Building Services, Laing O’Rourke and others (PrefabAUS, 2014).

2.5.8 Previous Studies Performed on Modular Building Systems

Several studies have been performed on most aspects of MBSs including structural

behaviour, economics, application to various building types (high-rise, industrial etc.),

and manufacturing and construction co-ordination. However, investigations of the

structural performance and behaviour of complete MBSs as a whole tower structure

are limited. This section briefly presents several completed and notable studies in the

MBSs field.

Handbook for the Design of Modular Structures

Researchers at Monash University (2017) formed a collaborative group with industry

professionals to produce the “Handbook for the Design of Modular Structures”. The

very recent publication is a conglomerate of design principles for the design of MBSs

with guides specific to meeting Australian Standards. It is the closest resemblance of

a document pertaining to the structural design of MBSs in Australia. The authors have

expressed that the handbook is only meant to serve as a guide and not a standards

specification document. The authors also expressed that the handbook was created to

pave the way for a standards specification document specific to the design of MBSs in

Australia to be developed.

Behaviour of Framed Modular Building System with Double Skin Steel

Panels

Hong, Cho, Chung, and Moon (2011), performed a thorough investigation on the

adoption of double skin steel wall panels in MBSs. Their research was performed with

the intention to investigate the cyclic behaviour of the new type of lateral load resisting


systems and the effect of their applications to steel frames. The new type of lateral load

resisting system was proposed as an alternative to steel plate shear walls. Steel plate

shear walls are noted to be relatively expensive given the high number of welding

connections. In addition, creating wall openings in steel plate shear walls are

considerably difficult.

The proposed alternative is a steel framed modular system incorporating double skin

steel wall panels as shown in Figure 2-47. The panels consisted of a corrugated steel

core sandwiched by two steel sheets as shown in Figure 2-48. The steel corrugated

steel core was implemented to prevent premature local buckling of the steel sheets.

The steel sheets were soldered to the corrugated metal core to ensure that an even

surface was maintained on the thin base metal (steel sheets).

Figure 2-47: Framed modular system with double skin steel wall panels (Hong et al., 2011).

Figure 2-48: Double skin steel panel (Hong et al., 2011).

Both theoretical analysis and full-scale testing were performed. Dynamic analyses of

the hysteretic behaviour of the systems were derived using an earthquake engineering

simulation program. Experimental testing was performed on four steel panel

specimens and three modular system specimens.


The study found that incorporating the double skin, steel wall panels produced lateral

stiffness (4.00 kN/mm) four-times greater than the same steel frame without panels

(1.00 kN/mm). In addition, the steel wall panels yielded first before the steel columns

indicating a sense of control in preventing severe damage to the frame which is

employed as the primary structural system. Concluding, the lightweight, steel panels

demonstrated their capability to be an effective supplementary lateral force, resisting

systems with single-wall hysteresis capable of defining their behaviour.

Modular Design for High-Rise Buildings

Professor Robert Mark Lawson of the University of Surrey is renowned for his

extensive investigations, works and publications in the field of MBS. Recently,

Lawson co-authored a paper with Richards titled “Modular Design for High-Rise

Buildings”, (R. M. Lawson & Richards, 2009). The paper presented a discussion of

the application of modular design to high-rise buildings, and the results of

experimental tests and analysis of light-weight steel modular walls in compression.

Lawson and Richards present several examples of modular constructed high-rise

buildings and relative case studies. They advise that reinforced concrete or steel-plate

cores must be adopted to provide lateral stability for MBS of great height. Lawson and

Richards also discuss the complex structural behaviour of high-rise MBS. They

attribute this behaviour to the influence of the implicit construction tolerances during

the installation procedure, the multiple interconnections between the modules and the

process of transferring the forces to the stabilising elements such as the core walls.

Lawson and Richards prescribed the following design considerations:

• The influence of initial eccentricities and construction tolerances on the

additional forces and moments in the walls of the modules;

• Application of the design standard for steelwork, BS 5950-1 to modular

technology, using the notional horizontal load approach;

• Second-order effects due to sway stability of the group of modules,

especially in the corner columns;

• Mechanism of force transfer of horizontal loads to the stabilising system,

for example concrete cores; and

• Robustness to accidental actions (also known as structural integrity) for

modular systems.


Experimental tests and analyses were conducted to investigate the structural action of

the load-bearing walls in a typical modular building system. Specifically, the

experiments sought to study the compressive resistance of C sections, spaced at

300mm intervals, taking into the account of the restraining and stiffening effects of

various types of boards. The experiments also investigated the sensitivities to

eccentricities up to 20mm; considered to surpass the maximum envisaged tolerable

amount. The wall panels were loaded using a spreader beam. Further details of the

configuration and arrangement used in the tests is seen in Figure 2-49.

Figure 2-49: Test arrangement used in Lawson’s and Richard’s study (R. M. Lawson &

Richards, 2009).

The results of the test indicated that plasterboards and external sheathing boards

effectively prevent minor axis buckling of the C sections and hence failure occurred

by either failure of the major axis or crushing of the section. In comparison to the

predicted strength given by application of BS 5850-5, it was found that all tests

involving the use of 75mm and 100mm deep sections of 1.6mm thickness exceeded

their predicted failures by 0 to 40%. When a 20mm load eccentricity was introduced,

a reduction in capacity of 8 to 36% was witnessed; attributed to the local crushing of

the C sections.

2.5.9 Transportation

Frequently overlooked but highly critical to the success of a modular construction

project is the transportation phase of module units from plant to site. Units should


arrive to site intact, on time and with minimal costs. In the UK, the National Audit

Office (2005), determined that Transport and equipment account for 7% of the overall

costs in modular construction of multistorey residential buildings. Coordination of this

process is crucial, and many factors need to be taken into consideration. This section

will present these factors.

When enroute to site, transported goods are exposed to changing environments leaving

them susceptible to a variety of events with detrimental effects. To mitigate these

issues, the goods should be properly secured and protected. A series of fasteners and

straps appropriately fixed will ensure the goods are secured to the transporting vehicle.

Weather seals, plastic wraps, cardboard or even wooden crates and shipping containers

can be used to protect the goods from the changing environments.

Both damage to the transported goods and transport infrastructure can occur when en

route to site. Local governing bodies have set regulations to minimise the occurrence

of these events. Often, the size of modular units is not restricted by engineering

capabilities but rather the conditions that govern the transportation process of the

modular units. Conditions which include dimensional limits, combined mass limits,

physical obstructions along the route and structural capacities of the transport

infrastructure.

The planning of the route and schedule of deliveries is a major factor in the success of

the transportation phase. Numerous variables must be accounted, with several

unpredictable in nature and constantly changing. Variables to consider include:

• Mode of transport – road, rail, sea or air;

• Selection of transport vehicle – form, capacity and operating requirements

(fuel consumption, required operators, drivers etc.);

• Selection of route – road topography, profile, gradients, climb, descent,

width and obstructions (sign posts heights, overpasses etc.);

• Supporting infrastructure – loading bays, shipping, rail yards, airports and

infrastructure along the route (bridges, crossings and culvert capacities);

• Imposed conditions of travel – speed limit, customs, checkpoints etc.;

• Time of travel – weather conditions, visibility and traffic conditions (critical

routes, peak traffic hours etc.);


Generally, the local governing transport body will enforce conditions which consider

most of the above variables. In Australia the governing body that regulates the

conditions of heavy vehicle road transportation is the National Heavy Vehicle

Regulator (NHVR). The enforcing document is the Heavy Vehicle National Law Act

2012 – Heavy Vehicle (Mass, Dimension and Loading) National Regulation.

2.5.10 Assembly and Installation

Once module units have been manufactured and delivered to site, the assembly of the

building by installation of modules can take place. The assembly phase includes secure

hoisting and lifting of the units into position. Careful consideration of the method of

hoisting must be made, as forces exerted on the module can be greater during

installation than during its service life.

The assembly stage begins with the preparation of modules by removing weather

sealing and other protective measurements put in place for the transport of the modules

to site. Next, hooks, beams, load spreaders and other necessary attachment

mechanisms are set in place, ready to be hoisted by the crane. Unstable and fragile

units (often larger modules or weak open-sided modules) will require extra attention

and care which can be provided with the use of a supplementary bracing system. When

ready, several teams coordinate the hoisting and positioning of the module unit into

place. Once in place, the modules are connected to the other in-placed modules through

a method called jointing. To finish off the assembly phase, weatherproofing of the

modules and joints is completed.

Modular buildings are erected in a horizontal process and are organized floor by floor.

The time coordination of the assembly process is paramount to the project success.

Project planners must accurately estimate and coordinate the exact time to deliver,

prepare, hoist, position and connect a module. In doing so, congestion of deliveries at

site can be avoided.

Generally, modules are lifted at their corners using inclined cables or through the

assistance of a spreader beam or frame. In some cases, modules may be lifted from

their bases but often this is avoided to minimize potential damage to the base. Figure

2-50 presents several arrangements of module to crane connections.


Figure 2-50 General module to crane connection arrangements (M. Lawson et al., 2014).

In the arrangements where cables are inclined at the connections, additional horizontal

forces will be exerted throughout the modules. It is preferable that the additional forces

exerted on the modules are limited to only vertical forces and hence, lifting beams and

frames are incorporated to reduce the horizontal loading. The most preferred method

of arrangement is by using a two-dimensional frame (bottom right of Figure 2-50).

Jointing

In the construction of structures, jointing describes the process of how two or more

elements are connected and joined. In buildings, joints appear where building elements

meet, enclosing a void of space. The layout of joints is determined by the size, shape

and dimensions of the building elements and thus has a heavy influence on the

appearance of façade as shown in Figure 2-51. Often the voids at the joints are not

completely closed and moisture is capable of penetrating through, leaving the structure

exposed to several adverse effects. To combat this, the joint is protected against

moisture by use of a sealant in addition to other constructional solutions.


Figure 2-51: Building joints influencing the appearance of a façade.

Tolerances

Vital to the structural performance of a structure is the permitted tolerance. In this

regard, tolerance refers to the possible difference between the nominal and as-built

dimensions of the structure. The slightest deviation in placement or misalignment can

result in catastrophic consequences especially in large structures where loads are of a

very high magnitude. For this reason, the connection and jointing systems of the

structure should be designed to expect, allow and tolerate these deviations without

adverse effects to the structure’s performance.

Tolerance should be thoroughly planned and considered during the design and

planning phases especially in the case of modular systems, where modules are often

repetitive designs and the possibility to make changes to the structure on site is very

difficult. Several connection systems to allow for tolerances include implementation

of elastic joints and bearers, and oblong holes for screw fixings.

There are several sources throughout the life cycle of a modular structure that can

contribute to deviations of the dimensions. These deviations are most likely to occur

during the manufacturing and assembly phases with physical damage during transport

an unlikely event. M. Lawson et al. (2014), stated that for the case of light-weight,

steel frame modules, manufacturers can accurately, mass produce modules within an

error margin of +1 to -3mm. This margin appears very minute; however, a series of

modules with these deviations will accumulate to a very significant sum.

During the assembly phase, there are several events which may contribute to a change

in the dimensions of the modules. Given modules can amass to a self-weight of over

20 tonnes, flexing of components will occur during any lifting phase i.e. from factory

grounds to truck, truck to construction site and during installation on site. The degree


of flex and whether permanent or temporary damage occurs is dependent on the

material properties of the components and the arrangements used to lift the module.

Mitigation of flex during lifts can be completed by employing spreader beams,

temporary bracing measures and dedicated load-tie arrangements.

Another event during the assembly phase that can contribute to dimensional deviations

is the event of positioning and installing modules. The accuracy of placement and

positioning is controlled by the crane operators and dedicated installation labourers

any deviations from this event will be of human error. To minimize the degree of

human error in the placement of modules, high precision global positioning system

(GPS) devices can be employed to assist with the process.

The consequences of having dimensional deviations from designed specifications to

as-constructed specifications can be of very high calibre. The two most prevalent

consequences are structural performance and aesthetic appeal. The most critical

dimensions to be aware of are the plan (horizontal) dimensions, as shown in Figure

2-52(a). Variations in horizontal alignments will reduce space between modules, lifts

and other services which can lead to misalignment with foundations. Variations in

vertical alignments can cause modules to extrude outwards becoming wedge shaped,

as shown in Figure 2-52(b). Vertical alignment is critical for modular structures of 6

or more stories (M. Lawson et al., 2014).

Figure 2-52: Effects due to misalignment (M. Lawson et al., 2014).

2.6 FINDINGS, SUMMARY AND IMPLICATIONS

2.6.1 Cold-formed Steel

Researchers at the QUT have recently developed a new, innovative and improved CFS

section called the Rivet-Fastened Rectangular Hollow Flange Channel Beam. The


Rivet-Fastened RHFCB was developed as an alternative to the LiteSteel Beam, a

discontinued CFS section superior to traditional CFS sections in terms of weight,

strength and design application. The creators of the Rivet-Fastened RHFCB believe

the section also shares similar, if not greater, strength reserves of the LiteSteel Beam

amongst other favourable properties. Current works are underway to further

investigate the structural behaviour of the Rivet-Fastened RHFCB, with completed

findings concluding:

• Preliminary evidence supporting AS/NZS 4600’s prescribed EWM is

suitable for calculating the section moment capacity of Rivet-Fastened

RHFCB with rivet spacing up to 100mm. Although, effects of intermittent

rivet fastening cannot be included in the EWM.

• Preliminary evidence supporting that the DSM can reasonably well predict

the section moment capacity of Rivet-Fastened RHFCB with provisions to

account for the effects of intermittent rivet fastening.

• Application of AS/NZS 4600 for determination of the shear capacity of

Rivet-Fastened RHFCB yields very conservative results. As such, suitable

equations based on the DSM have been proposed and are recommended for

use only for sections with 100mm rivet spacing pending further research.

• Application of AS/NZS 4600 for determination of the web crippling

capacity of Rivet-Fastened RHFCB yields inaccurate results of varying

degrees. As such, new equations have been proposed to determine the web

crippling capacity of Rivet-Fastened RHFCB with 100mm rivet spacing.

2.6.2 Modular Construction Technology

The modular construction method is gaining popularity as an alternative to traditional

construction methods. This popularity increase can be attributed to the numerous

benefits that the modular construction method offers over traditional methods. The

main benefits include:

• Faster project delivery times;

• Significant project costs reductions;

• Greater quality control and reduced waste; and


• Minimized health and safety concerns involved in construction of the

structure.

Although, for a modular building project to deliver such benefits, it is crucial

that extensive planning is executed in all phases of the project. The modular

construction project is very much an interconnected and integrated design process.

Changes in one phase of the project are highly likely to result in changes in one and

usually more other phases of the project. Hence, due consideration must be made to:

• Structural Design;

o Types of modular systems – there are three general types of modular

systems; fully modular construction, modules supported by a separate

bracing system and non-load bearing pods.

o Types of steel modules – there are four general types of modules; four-

sided modules, partially-open sided modules, corner supported modules

and open-ended modules. The type of module selected will usually be

influenced by architectural requirements and this choice will influence

the structural behaviour of the entire structure.

o Module materials – common materials chosen for the structural frame

of modules include wood, concrete and steel. Steel is the most common

choice, given its broad structural capabilities, predictable behaviour,

high strength-to-weight ratio and wide availability.

o Current design codes – presently in Australia, there does not exist a

solely dedicated design code for the modular structures. At best, a

designer wishing to design a modular structure should design the

structure using the most relevant and existing design, often dependent

on structural material chosen, and should consider the overall structural

behaviour of the modular system.

o Manufacturing considerations – the structural design of modules will

be heavily influenced by manufacturing factors. Factory capabilities are

to be considered and the system should be easy to mass produced within

a small period.

o Connections – connections are a key component to the success of a

modular construction project. Ease of connections heavily influence the

installation time and should be designed to provide minimal degree of


difficulty when installing, sufficient strength and be relatively easy to

mass-produce.

o Bracing – several bracing systems can be employed in modular

structures, dependent on the structure’s height, the type of modular

system chosen and its interaction with individual modules. Stability of

individual modules should also be considered when the module is

undergoing production and being hoisted into place.

o Tolerances – the difference in designed and as-built structural

dimensions (tolerance) is attributed to two events; manufacturing and

installation. Tight manufacturing controls can minimize tolerance

values. Employing advanced GPS technologies can minimize

installation tolerances. Though, complete elimination of tolerance is

highly unlikely and hence the structural designer must incorporate

measures to allow for tolerances. This usually details in the design of

connections. Exceeding tolerance values can result in disastrous effects,

both aesthetically and structurally.

• Manufacturing;

o Location - the factory should be within proximity to the project site to

minimize transportation costs. In some cases, it can be beneficial to

establish a field factory. The chosen factory location should also

provide sufficient room for manufacturing of modules as well as storage

and stockpiling of completed modules.

o Manufacturing process design - extensive planning is required in design

of the production process to produce modules quickly, efficiently and

economically. Two main processes currently exist, which are linear and

static production, as well as hybrid combinations of these processes.

Manufacturing process and structural design are interrelated,

influencing each other in all details.

o Factory layout – the factory layout will heavily depend on the details of

the production process. The layout of the factory should be systematic,

orderly and with sufficient room to allow storage and stockpiling of

materials and completed modules.

• Transport;


o Transport mode type - the selection of transport type will be influenced

by proximity of project site to manufacturing factory, topography,

existing infrastructure and economic circumstances.

o Local governing restrictions - road transport authorities have existing

restrictions on transporting large loads such as completed modules.

Often, the size of the module is restricted by transport restrictions as

opposed to structural capabilities. Restrictions may include size

limitations, time of delivery, restricted routes and safety measures such

as lighting and accompanying escorts.

• On site assembly and installation; and

o Site layout - the layout of the site should consider stockpiling of

modules, free flow delivery measures and crane and hoists spacing

requirements

o Modules should be able to be safely and quickly installed which is

heavily reliant on hoisting details and connection detailing.

• Project Delivery.

o BIM Software - Numerous benefits are offered by modular construction

but employing the method requires immense coordination between

planning, design, manufacturing, delivery and installation. To

maximize the benefits on offer, employing BIM software is a must and

will streamline the entire process. In a single package, BIM software

can coordinate planning, design, manufacturing and management.

2.6.3 Conclusion

As explored above, there exists an opportunity to advance the development and

address the shortcomings of modular construction technologies through implementing

recent innovative developments. This chapter has presented the potential benefits of

modular construction technologies and demonstrated the need to refine and realise this

technology. Realising these opportunities will result in increased savings, faster

construction times and greater sustainability of modular construction technologies.


Chapter 3: Case Studies

3.1 INTRODUCTION

The 21st century has seen a rapid increase in the number of modular constructed

buildings, particularly in the market of high-rise structures. The increase is attributed

to many factors but generally, it is due to the advancing technologies that allow

modular structures to reach greater heights and address shortcomings. This section

presents and reviews several complete modular structures as well as individual system

components (connections, walls and floors) paying specific attention to the

technologies that allow modular construction to achieve such feats. Specifically, the

following case studies are examined:

• MBS: 461 Dean, New York City (Section 3.2);

• MBS: SOHO Apartments, Darwin (Section 3.3);

• MBS: Octavio’s and Pascual’s Affordable Steel Concept (Section 3.4);

• MBS: The Verbus System (Section 3.5);

• Component - Wall: Double Skin Steel Panel Wall System (Section 3.6);

• Component - Connection: VectorBloc Connection System (Section 3.7);

and,

• Component - Connection: Connector System for Building Modules by

Verbus Systems (Section 3.8).

All the case studies in this section are projects completed within the last 10 years. They

represent the epitome of the MBS field for which ideas and designs can be built upon

to continue achieving faster, stronger and better results.

3.2 461 DEAN, NEW YORK CITY.

3.2.1 General

Generating large interest in the multistorey and modular buildings sectors was the

delivery of 461 Dean (previously known as Tower B2) by developer Forest City Ratner

in partnership with construction company Skanska (former). The 32-storey modular

building is currently tallest modular constructed building in the world. 461 Dean is


located in Brooklyn, New York City as part of the Pacific Park development project

(previously known as Atlantic Yards). The building was constructed with intentions to

provide affordable housing to the growing New York City market and intentions to

demonstrate the capabilities and benefits of employing modular construction

techniques on high rise buildings. The building comprises of 930 modules forming 363

apartments. Summary project details of the building are presented in Table 3-1 with a

visual rendering presented in Figure 3-1.

Table 3-1: Summary project details of 461 Dean, New York City.

Project Name 461 Dean

Location New York, USA

Owner Forest City Ratner Companies, Greenland Holding’s and

Skanska (previous)

Architect SHoP Architects

Structural Engineer Arup

Construction

Company Forest City Ratner Companies and Skanska (previous)

Construction

Commencement 2012

Construction

Completion November, 2016

Project Value B2 BKLYN Tower (unknown)

Pacific Park Development ($4.9 billion)

Number of Floors 32

Number of Modules 930

Project Size 32144.5 m2 (346000 ft2)

Figure 3-1: 461 Dean of the Pacific Park development project, New York (Dezeen Magazine

2012).


3.2.2 Structural Review – Tower Structural Scheme

SHoP Architects led the architectural design of the building with Arup given the

responsibilities of structural and mechanical engineering design. The structure adopts

a steel-framed modular system design and comprises of a lower podium that supports

19 stories of modules above. The arrangement of these modules is essentially in the

form of 3 distinct building masses (left, centre and right) as seen in Figure 3-2.

Figure 3-2: Structural scheme of the 461 Dean tower (Forest City Ratner Companies, 2012).

The main bracing system occupies the centre building mass and consists of individual

braced frames joined together at the roof level with a hat truss. Sufficient module-to-

module (lateral and vertical) connections allow the modules to support their own

stability without the aid of the braced frames when subjected to service conditions.

The generic floorplan of B2 BKLYN Tower is presented in Figure 3-3. The largest

floorplan comprises of 36 modules in its floor.

Figure 3-3: Generic floorplan of 461 Dean Tower (FC Modular, n.d.).


3.2.3 Structural Review – Module Structural Scheme

Module Chassis

Given the various architectural features desired, a total of 225 unique modules were

designed for the B2 BKLYN Tower, ranging in weight from 7 tonnes to 24 tonnes.

The base chassis of the modules forming the B2 BKLYN Tower is presented in Figure

3-4 with further details about the structural components presented in Table 3-2.

Figure 3-4: Structural scheme of base module chassis employed in the 461 Dean tower

(Forest City Ratner Companies, 2012).

Table 3-2: Structural components of the base module employed the 461 Dean tower.

Chassis Structural

Component Section Profile

Size (Typical)

(inch) (mm)

Column (Corner) Square Hollow Section 6 x 6 150 x 150

Column (Intermediate) Rectangular Hollow

Section 3 x 2 75 x 50

Chord (Bottom) Rectangular Hollow

Section 8 x 4 200 x 100

Chord (Top) Square Hollow Section 4 x 4 100 x 100

Weatherproof Membrane Class A Building Wrap 2 layers of

5/8

2 layers of

16

Strap Bracing Flat Plate 10 250

The base chassis adopts a fully-welded, open-ended module design that consists of

thicker members located in the end frames and rigid connections to support the

redirected load. The base chassis assembly consists of large 150mm x 150mm SHS

that form the corner columns of the chassis with interconnecting links made by 100mm

x 100mm SHS (roof chords) and 200mm x 100mm RHS (floor chords). The closed

SHS of the roof chord members along with the decking form a lateral diaphragm that


carries lateral loads to the braced frames of the tower structure. Completed module

chassis are shown in Figure 3-5 and Figure 3-6.

Figure 3-5: Side view of completed a 461 Dean module chassis (Calcott, 2014).

Figure 3-6: End view of completed a 461 Dean module chassis (Calcott, 2014).

Wall System

The wall system of the base module used in the construction of the 461 Dean Tower

is presented in Figure 3-7 with further details on the structural components presented

in Table 3-3.

Figure 3-7: Constructing the wall system of the modules of the 461 Dean tower (FC Modular,

2015).


Table 3-3: Structural components in the wall assembly of the base module employed in the 461

Dean tower.

Wall Structural Component Section Profile

Wall Column CFS Stud

Wall Chord (Bottom) CFS Edge

Wall Chord (Top) CFS Edge

Wall Lining Gypsum Board 16mm

Weatherproofing Protection Ethylene Propylene Diene Monomer

Within the open-ended module design, the configuration of vertical members in the

side panels are laid out in the form of a Vierendeel Truss system. The intermediate

posts in the side panels are 75mm x 50mm RHS. Thin gauge steel in the form of

250mm flat plates are aligned diagonally in along the side panels to serve as strap

bracing elements.

Roof System

The roof system of the base module used in the construction of the 461 Dean Tower is

presented in Figure 3-8 with further details on the structural components presented in

Table 3-4.

Figure 3-8: The roof assembly of the base module of the 461 Dean Tower.

Table 3-4: Structural components in the roof assembly of the base module employed in the 461

Dean tower.

Roof Structural

Component Section Profile

Size (Typical)

(mm) (inch)

Weatherproof

Membrane

Ethylene Propylene Diene

Monomer (EPDM) 1 0.045

Outer Shell Ribbed Cladding 25 1

Purlin Square Hollow Section 75 x 75 3 x 3

Furring Furring Channel 22 7/8

Ceiling Board Gypsum Board (Type X) 2x layers of

16

2x layers of

5/8


The roof system consists of longitudinally directed 25mm ribbed decking supported

by 75mm x 75mm RHS purlins that are attached to the 100mm x 100mm RHS top

chords of the base module chassis via fillet welds. Fastened to the underside of the

purlins and running longitudinally are 22mm furring channels that support the 2 layers

of ceiling Type X1 Gypsum boards (16mm each). Completing the assembly is a 1mm

thick layer of ethylene propylene diene monomer (EPDM) weather proof membrane

placed atop of the ribbed decking.

Floor System

The floor system of the base module used in the construction of the 461 Dean Tower

is presented in Figure 3-9 with further details on the structural components presented

in Table 3-5.

.

Figure 3-9: The floor assembly of the base module employed in the 461 Dean tower

Table 3-5: Structural components in the floor assembly of the base module of the 461 Dean

tower.

Floor Structural Component Section Profile Size (Typical)

(mm) (inch)

Insulation Acoustic Padding 5 1/4

Floor Board Cementitious Particle Board 19 3/4

Decking Ribbed 50 2

Purlin Rectangular Hollow Section 150 x 75 6 x 3

The floor system consists of a 19mm layer of cementitious particle board fastened to

50mm ribbed decking running longitudinally. Supporting the decking are 150mm x

75mm RHS purlins which are attached to the 200mm x 100mm RHS bottom chords

1 Type X Gypsum Wall Board as per New York City Building Code 2008.


of the base module chassis via fillet welds. Completing the assembly is a 5mm layer

of acoustic padding atop of the floor board and sandwiched by the floor finish

(typically hardwood).

3.2.4 Performance Review

General

Intended to display the capbilities of modular construction, the delivery of the 461

Dean modular structure did not meet expectations. Forest City initially claimed to

deliver the tower in 18 months and at a considerably lower cost relative to traditional

construction methods but due to contractor disputes and other issues the construction

length of 461 Dean was almost doubled. Delivery and installation of the first module

occurred on December 12th, 2013 (one year after the intended start date) and the

structure was topped out in May, 2016 and fully completed almost 3 years later in

November, 2016.

Contract issues between Forest City and Skanska were the main factors contributing

to lengthy delays and disruption in the project. Forest City claims that Skanska had

failed in their execution of the contract and Skanska claims the design of the modules

from Forest City were faulty and had led to cost overuns on their behalf. Forest City

maintains that Skanska signed a fixed price contract and any cost overuns are the

responsibility of Skanska. Efforts to resolve the differences between the two

companies led to Forest city buying out Skanska’s stake in the project to continue

works.

The faulty module design claims from Skanska stem from the overly tight (often

exceeding standard industry practice) construction tolerances imposed by Forest City.

In addition, Skanska claims that Forest City’s design lacked adjustability with only a

single source of adjustability provided whereas in typical steel frame buildings, four

sources of adjustability would be provided.

Construction and Quality Performance

The construction of 461 Dean saw severe misalignment issues arise. The misalignment

of the modules is highly evident on the 10th floor and as depicted in Figure 3-10. As

a result of the misalignment, the building was left susceptible to weatherproof issues

during the installation of modules phase.


Figure 3-10: Misalignment of modules as seen on the 10th floor of the 461 Dean Tower (Oder,

2015).

During the court proceedings, it was observed that the match plates (3/8” thick) which

join the modules together were flawed in design. The engineering drawings produced

by the designer showed a 1/4” tolerance between columns in the modules was

permitted. Though, the bolt holes in the match plates only permitted a tolerance of

1/16” in horizontal movement. As a result of the error, the designer agreed to enlarge

the match plate hole diameter to 1 3/4".

In lieu of the misalignment issues, the simple steel structural design of the base chassis

forming the modules in 461 Dean has proven structurally adequate to support a high

rise structure. In addition, Farnsworthy (2014) notes that with the absence of concrete

in the structure of 461 Dean has resulted in the building weighing approximately 65%

of conventional reinforced concrete flat slab buildings.

3.2.5 Conclusion

The 461 Dean project is currently the world’s tallest modular building. The thick,

although heavy, steel members forming the module chasses provide sufficient capacity

to withstand the vertical loads. The effective, although complex, external, skeleton

bracing system ensured the building had sufficient lateral loading capcity.

Besides the hieight accomplishing feats, the 461 Dean project s has not been the best

example of modular construction use in multistorey buildings. Ineffective module

design has lead to severe misalignment of the modules and leading to further troubling

structural concerns such as weather-proofing issues during construction. Fortunately,

the designers were able to adjust the existing design to address the misalignment

issues.


3.3 SOHO APARTMENTS, DARWIN

3.3.1 General

In September of 2014, developer and builder - Gwelo Developments, completed

construction of a 29-storey modular structure in Darwin, Australia. Valued at $120

million, the project proposed to address the severe housing demand in Darwin during

the offshore gas boom. The building is currently owned by Minor Hotel Group and

through their subsidiary - Oaks Hotels and Resorts, a 4.5-star hotel is operated in the

building with commercial and retail tenants occupying the lower floors and apartments

forming the upper floors. Given the constrained labour market and the soft soil

conditions of the site, modular construction was utilised to address the shortcomings

of these conditions. Further details of the project are presented in Table 3-6 and a visual

rendering of the completed structure is shown in Figure 3-11.

Figure 3-11: SOHO Apartments of Darwin, Australia.

Table 3-6: Project details of SOHO Apartments, Darwin.

Project Name SOHO Apartments, Darwin

Location Darwin, Australia

Owner Gwelo Developments Pty. Ltd.

Architect DKJ Projects and Sidecart Studios

Structural Engineer Irwinconsult

Construction Company Gwelo Developments Pty. Ltd.

Construction Commencement March, 2012

Construction Completion September, 2014

Project Value $120 Million

Number of Floors 29 (21 Modular)

Number of Modules N/A

Project Size N/A



Irwinconsult have utilised both steel and concrete elements in the design of this

modular tower (see Figure 3-12). The structure consists of 21 modular constructed

storeys supported on top of an 8-floor concrete podium. The modular structure utilises

a complex vertical loading system. During the transportation and installation phases,

vertical loading is supported by the steel columns alone. When installed on site, insitu

concrete is casted into these steel columns to form hybrid concrete-steel columns that

together act as the vertical load bearing members of the tower for its entire service life.

Lateral loading is addressed with a concrete core and individual module bracing.

Figure 3-12: SOHO Apartments structural arrangement (Irwinconsult, 2014).


Module Chassis

Built in Ningbo, China, the module chassis comprises of both concrete and steel

elements. The module chassis is presented in Figure 3-13 and further details of the

structural components presented in Table 3-7.

Figure 3-13: Structural scheme of the base module chassis employed in the SOHO Apartments

structure (Irwinconsult, 2014).


Table 3-7: Structural components of the module chassis employed in the SOHO Apartments

structure.

Chassis Structural Component Section Profile

Column (Corner) Combined Steel Flat Plate-Insitu Concrete

Column (Intermediate) Combined Steel Flat Plate-Insitu Concrete

Floor System Precast Concrete Floor Slab

Insulation Spray Polyurethane

Roof System Precast Concrete Ring Beam

Strap Bracing Steel Flat Plate

The layout of the elements resembles a portal frame structure, with intermediately

spaced frames and other similar traits. The module’s chassis is a hybrid partially open-

sided module with one end frame designed as an opened end. Irwinconsult have

utilised a truss system instead of employing thicker members for the opened end frame.

The vertical truss components adopt the Warren Truss form and the horizontal

components adopt the Double Warren Truss form.

Steel columns act as formwork for insitu concrete columns to be casted on site. The

steel columns have been designed with enough structural capacity to allow the modules

to be stacked four modules high during transport. A concrete ring beam encloses the

top of the module. A lightweight concrete slab forms the floor of the module. Steel flat

plate sections are utilised as strap bracing members along the walls to address the large

lateral loads during transportation. End bay bracing was also achieved with diagonally

aligned steel flat plates. Overall lateral stability of the structure is achieved through a

central concrete core. The concrete floor slabs of the modules transfer their loads to

the corridor slabs and onto the outrigger walls running from the central concrete core.

Wall System

Irwinconsult have developed a complex wall system to withstand the large vertical

loading of the tower structure. The wall system utilises the combination of steel and

concrete technologies as depicted in Figure 3-14 and detailed in Table 3-8.

Figure 3-14: Side view of a completed SOHO Apartments module. (Skyscrapercity.com, 2014).


Table 3-8: Structural components of the wall system employed in SOHO Apartments structure.


Column (Corner) Combined Steel Flat Plate-Insitu Concrete

Column (Intermediate) Combined Steel Flat Plate-Insitu Concrete

Wall Column CFS Stud

Wall Chord (Bottom) CFS Section

Wall Chord (Top) CFS Section

Strap Bracing Steel Flat Plates

Outer Shell Ribbed Steel Sheets

Heavy gauge steel sections form the columns of the wall system with placement in the

corners and at intermediate intervals along the wall. These steel columns act as the

main structural vertical load bearing members of the modules during the transportation

and installation of modules. The columns possess enough structural capacity to allow

the stacking of modules up to four modules high during transport and installation.

When the modules are placed next to each other, the steel columns create a void of

enclosed space and essentially form the formwork required for insitu concrete columns

to be cast on site. This now completed steel-concrete column acts as the main vertical

load bearing member of the tower structure.

Between the columns, wall frames are formed with the use of CFS sections as the top

chord, bottom chord and intermediate wall studs Diagonally aligned steel flat plates

are employed as strap bracing components providing lateral support. Ribbed steel

sheets are employed as the cladding components providing further structural capacity

as well as weather protection.

Roof System

The ceiling system, best depicted in Figure 3-15 and detailed in Table 3-9, comprises

of a concrete ring beam enclosing intermediately-spaced truss systems and CFS beams.

Figure 3-15: Module arrangement in SOHO Apartments, Darwin (Irwinconsult, 2014).


Table 3-9: Structural components of the roof system employed in the SOHO Apartments

structure.

Roof Structural Component Section Profile

Chord Precast Concrete Ring Beam

Roof Joist (Primary) CFS Section (Intermediate Placement Arrangement)

Roof Joist (Secondary) CFS Section (Truss Form Arrangement)

Ceiling Board Plasterboard

Outer Shell Thin Flat Steel Sheet

The concrete ring beam is cast during the fabrication of the module. Purlins are formed

with CFS sections placed at intermediate spacing. These are complimented with

another set of purlins in the arrangement of a truss system (Warren Truss form) and

are aligned with the insitu concrete columns. Bolted connections are used to join the

truss system to the heavy gauge steel formwork of the insitu columns.

Floor System

A 125mm thick concrete slab forms the floor of the modules as shown in Figure 3-16.

Figure 3-16: Lifting of the modules forming the SOHO Apartments tower.

Table 3-10: Structural components of the floor system employed in the SOHO Apartments

structure.

Floor Structural Component Section Profile

Floor Concrete Slab

Floor Finishing Tile/Polished Concrete Slab Floor

Irwinconsult designed the concrete slab with perimeter beams and cross beams which

align with the vertical load bearing position of the columns. This arrangement reduced

the overall thickness of the concrete slab resulting in weight reduction too. The

concrete slab is constructed off-site in alignment with the rest of the module.


The lightweight concrete mix design forming the floor slab targeted an initial density

of 1600 kg/m3 that could achieve a consistent specified strength. In practice, this target

was difficult to achieve and thus the design of the modules was modified. A specific

batching plant was set up for the lightweight concrete mix design to ensure strict

quality control.


General

SOHO Apartments, Darwin is currently Australia’s tallest modular structure.

Innovative structural designs and techniques made the feat possible in a remote and

cyclonic wind region designated site. The structure utilises a concrete podium and

concrete core stability system to stack 21 floors of concrete-steel modules. A prototype

all-steel module was proposed for the structure, however due to several requirements

concrete replaced several steel members and proved to be quite a beneficial decision.

Utilising concrete for the ring beam, columns and floors resulted in all the major

structural load bearing elements being concrete. As this was the case, Irwinconsult

were obliged to only provide fire protection for the concrete elements and not the steel

elements. This avoided difficulties in providing enough protection for the heat

vulnerable steel elements.


The drawback of using this system is the additional time needed for preparing, pouring

and curing of the insitu concrete elements. Although, by designing the module’s

chassis to withstand the stacking load of four modules, simultaneous pouring of the

insitu concrete and installation of modules was possible. In addition, the concrete core

could also be constructed independently, behind the stacking of the modules.

The modules were manufactured to a tolerance of +/- 10mm. For a stacked system of

21 levels, cumulative tolerance would prove worrisome. However, given the insitu

placement of the concrete columns, the modules could be adjusted appropriately.

Adjustment and installation of modules was labour intensive and time consuming.

The modules were assembled and manufactured in Ningbo of China and transported

to Darwin by sea freight. During the transportation of some modules, typhoon

conditions occurred and resulted in damage to some modules


3.3.5 Conclusion

The SOHO Apartments project is Australia’s tallest modular constructed structure.

The innovative approach of combining both steel and concrete materials to form the

chassis of the modules delivered enough structural capacity to permit the structure to

be built to great heights. Although in doing so, the speed of construction was decreased

to allow the concrete sufficient curing time. To mitigate this issue the designers

developed each module to be capable of withstanding the load of three modules above

without the assistance of the insitu concrete members, which allowed construction to

take place on the above storeys while the insitu concrete elements set.

The presence of thick steel and concrete members in the modules resulted in a heavy

design. The volume of materials used is relatively large and hence, expensive. In

addition, the on-site efforts required to assemble the modular tower structure is greater

than most other modular system designs. With all being said, given the location of the

project, employing modular construction remained more economical than traditional

construction methods.

3.4 OCTAVIO’S AND PASCUAL’S AFFORDABLE STEEL CONCEPT

3.4.1 General

As part of their postgraduate studies, Octavio and Pascual (2009) of Luleå University

of Technology (LTU), Sweden, developed a steel modular building system to

investigate affordable building concepts and to push for further use of steel in a country

that largely employs other building materials. Their proposed module design is

duplicated 74 times to form a five-storey structure that will serve as a student

accommodation complex. A conceptual drawing of the structure is presented in Figure

3-17 with general details of their project are presented in Table 3-11.

Figure 3-17: Octavio's and Pascual's modular tower structure (Octavio & Pascual, 2009).


Table 3-11: Octavio’s and Pascual’s Affordable Steel Concept – Project Details

Project Name Affordable House with Intensive Use of Steel (thesis title)

Location Luleå, Sweden

Owner Luleå University of Technology (LTU)

Architect Architect

Structural Engineer Xavier Octavio and Marta Pascual

Number of Floors 5

Number of Modules 74


Octavio’s and Pascual’s 5 storey tower structure adopts a fully modular concept, that

is to say, no podium, exoskeleton or additional bracing measures such as core walls

are employed in their tower structure. Modules are stacked upon each other with

module-to-module connections the only means of transferring horizontal forces.


Module Chassis

Octavio and Pascual adopted an open-ended module chassis design. The columns and

beams at the module ends are welded together. Figure 3-18 presents Octavio’s and

Pascual’s module design with Table 3-12 which details its structural members. Figure

3-19 presents the profiles of these sections with Table 3-13 presenting further details.

Figure 3-18: Octavio’s and Pascual’s Steel Module Design (Octavio & Pascual, 2009).


Table 3-12: Structural details of Octavio’s and Pascual’s module design.

No. Description Section Profile Quantity Location Orientation

(Direction) Notes

1 Primary Roof Beam UPE 220 2 Roof level. Lateral Welded to main column

2 Secondary Roof Beam UPE 160 2 Roof level, in longitudinal wall frame. Longitudinal

3 Supplementary Roof

Beam UPE 100 2 Roof level, borders. Lateral

Additional support

member

4 Primary Floor Beam UPE 220 2 Floor level, in longitudinal wall frame. Longitudinal Welded to main column

5 Secondary Floor Beam UPE 200 2 Floor level, borders. Lateral Additional support

member

6 Floor Joist C200x50x10x2 10 Floor level, in floor frame. Lateral 600mm spacing

7 Main Column UPE 220 4 In longitudinal wall frame, neighbouring the corner

members. Upright Welded to primary beam

8 Vertical Studs C70x34x1x0.7 21 Along both longitudinal walls and one lateral wall. Upright 600mm spacing

9 Rail Edge 70x43x0.7 4

Both ceiling and floor level, in longitudinal wall

frame, attached to primary floor beam (4) and

secondary ceiling beam (2).

Longitudinal Functions as guide for

vertical studs (8)

10 Corner Studs Angle 60x60x0.7 8 Corners. Upright Assembled in pairs


Table 3-13: Structural sections used in Octavio’s and Pascual’s module design.

Section Profile h (mm) b (mm) c (mm) t (mm) Weight per

metre (kg/m)

Angle 60x60x0.7 Angle 60 60 0 0.7 0.66

Edge 70x43x0.7 Edge 70 43 0 0.7 0.86

C70x34x1x0.7 Channel 70 34 1 0.7 0.77

C200x50x10x2 Channel 200 50 10 2 5.02

Section Profile h (mm) b (mm) tf (mm) tw (mm) Weight per

metre (kg/m)

UPE 100 UPE 100 55 7.5 4.5 9.82

UPE 160 UPE 160 70 9.5 5.5 17.00

UPE 220 UPE 220 85 12 6.5 26.60

UPE 200 UPE 200 80 11 6 22.80

Figure 3-19: Profiles of structural sections used in Octavio’s and Pascual’s module design

(Octavio & Pascual, 2009).

Octavio and Pascual have placed thicker steel members at the ends of the module

where the join between these members are a welded connection. Extending from the

end frame, CFS C-profile studs are grouped in pairs to provide adequate strength.

Between each end are thick UPE 220 beams that are welded to the end frames. CFS

vertical studs are placed at intermediate spacing between the end frames. Standard

module designs are typical in having intermediate spaced roof purlins. Though

interestingly, Octavio and Pascual have limited the number of roof beams to just being

the roof beams at the end frames of the module.

Composite Sandwich Façade

To address the severe cold-weather seen in Sweden, Octavio and Pascual have

designed a composite façade which is arranged in a sandwich profile. The arrangement

follows as two thin steel sheets sandwiching Polyurethane (PUR, 3% polyurethane +


97% gas) in between as depicted in Figure 3-20. Joining the sandwich panels together

is accomplished with concealed fasteners made possible with a clamp in the

longitudinal joint as depicted in Figure 3-21. The concealed fasteners arrangement is

depicted in Figure 3-21. Octavio and Pascual chose PUR as it exhibits the “lowest heat

transmission property of all commonly use thermal insulation materials” (Octavio &

Pascual, 2009).

Figure 3-20: Octavio's and Pascual's composite sandwich façade (Octavio & Pascual, 2009).

Figure 3-21: Arrangement of concealed fasteners in Octavio's and Pascual's composite sandwich

façade (Octavio & Pascual, 2009).

Wall System

Octavio’s and Pascual’s employed several wall profile designs. Though two general

wall profiles were adopted; interior walls and exterior walls. Figure 3-22 shows the

interior wall profile (a) and the exterior wall profile (b) and further details provided in

Table 3-14 and Table 3-15 respectively.

Figure 3-22: Wall profiles of Octavio’s and Pascual’s module design (Octavio & Pascual, 2009).


Table 3-14: Details of the interior wall profile of Octavio’s and Pascual’s module design

Interior Wall Structural Component Section Profile

Wall Column CFS Stud 70mm

Wall Chord (Bottom) CFS Edge 70x43x0.7

Wall Chord (Top) CFS Edge 70x43x0.7

Wall Lining Double Gypsum Board 13mm

Insulation Mineral Wool 70mm

Interior walls refer to walls which border against each other and are not exposed to

external environmental conditions. The interior walls, as depicted in Figure 3-22 (a)

and detailed in Table 3-14, consists of a double layer of gypsum board, followed by a

cavity of mineral wool surrounding the structural steel studs and then an empty void

of space separating the interior wall between another interior wall.

Table 3-15: Details of the exterior wall profile of Octavio’s and Pascual’s module design.

Exterior Wall Structural Component Section Profile

Wall Column CFS Stud 220mm

Wall Chord (Bottom) CFS Edge 220mm

Wall Chord (Top) CFS Edge 220mm

Wall Lining Gypsum Board 13mm


Weatherproofing Protection Plastic Film

Outer Shell Composite Profile

Exterior walls are referred to as walls which are exposed to external environment

conditions. Octavio and Pascual adopted an 80mm composite sandwich panel layout

for the façade which is attached to the exterior walls. Following the composite panel,

the exterior wall profile, depicted in Figure 3-22 (b) and detailed in Table 3-15,

consists of a gypsum board, a cavity consisting of the structural steel stud with infilled

mineral wool, plastic film and an enclosing gypsum board.

Roof System

Octavio and Pascual’s roof system are composed of six beams enclosed by several

panel elements. Similarly, like the wall systems, Octavio and Pascual have design two

roof systems; an interior system and exterior system. The interior roof profile is


presented in Figure 3-23 (a) with details given in Table 3-16. The exterior roof profile

is presented in Figure 3-23 (b) with details given in Table 3-17.

Figure 3-23: Roof profiles of Octavio’s and Pascual’s module design (Octavio & Pascual, 2009).

Table 3-16: Details of the interior roof profile of Octavio’s and Pascual’s module design.

Interior Roof Structural Component Section Profile

Roof Beam (Primary) UPE220

Roof Beam (Secondary) UPE 160

Roof Beam (Supplementary) UPE 100

Ceiling Board (Primary) Fire Resistant Gypsum Board 15mm

Ceiling Board (Secondary) Gypsum Board 13mm

Outer Shell Steel Sheet 45mm

Interior Roof Structural Component Section Profile

The interior roof system comprises of a sandwich arrangement of ceiling boards and

cladding. The ceiling boards are gypsum boards with the outer board being a normal

gypsum board and the inner board being a special fire-resistant type gypsum board.

Steel sheets of trapezoidal shape top the roof system as the cladding members.

Table 3-17: Details of the exterior roof profile of Octavio’s and Pascual’s module design.

Exterior Roof Structural Component Section Profile

Roof Beam (Primary) UPE220

Roof Beam (Secondary) UPE 160

Supplementary Roof Beam UPE 100

Ceiling Board (Primary) Fire Resistant Gypsum Board 15mm

Ceiling Board (Secondary) Gypsum Board 13mm

Outer Shell Composite 80mm

Weatherproofing Protection Plastic Film 2mm

Similarly, the exterior roof system comprises of a sandwich arrangement of ceiling

boards and cladding. The same gypsum boards arrangement is used, and the


trapezoidal steel sheet cladding is replaced with the composite board. Weatherproofing

protection is added in the form of a plastic film.

Floor System

Octavio and Pascual developed an interior and exterior floor system as shown in Figure

3-24 and detailed in Table 3-18 and Table 3-19 respectively.

Figure 3-24: Floor profiles of Octavio’s and Pascual’s module design (Octavio & Pascual, 2009).

Table 3-18: Details of the interior floor profile of Octavio’s and Pascual’s module design.

Interior Floor Structural Component Section Profile

Floor Beam (Primary) UPE 220

Floor Beam (Secondary) UPE 200

Floor Joist C Section 200x50x10x2

Floor Board Gypsum Board 2x layers of 13mm

Decking CFS Trapezoidal 45mm


The interior floor system comprises of two layers of gypsum boards on top of CFS

trapezoidal sheeting with mineral wool insulation all residing on the floor structural

chassis (primary floor beam, secondary floor beam and floor joists).

Table 3-19: Details of the exterior floor profile of Octavio’s and Pascual’s module design.

Exterior Floor Structural Component Section Profile

Floor Beam (Primary) UPE 220

Floor Beam (Secondary) UPE 200

Floor Joist C Section 200x50x10x2

Floor Board Gypsum Board 2 layers of 13mm

Decking CFS Trapezoidal 50mm


Outer Shell Composite 80mm

Weatherproofing Protection Plastic Film 2mm


Similarly, the exterior floor system has the same configuration as the interior system

apart from cladding now being the sandwich composite and the addition of plastic film

for weatherproofing.

Connection Details

Two connection types are present in Octavio’s and Pascual’s design, they are welded

connections and angle connections. The angle connections have been incorporated on

the corners of the modules, connecting the rigid members together. The first angle

connection (Figure 3-25(a) is comprised of two holes and connects the rigid ceiling

members. The second angle connection (Figure 3-25 (b) is comprised of four holes

and connects the rigid floor members. Both angle connections employ M-20 Class 6.8

bolts. All other connections used to assemble the module are fillet weld connections.

Modules to module connections along the horizontal direction are completed via four

bolts in each main column. In the vertical direction, module-to-module connections

are also completed by bolting with details of the bolts unspecified.

Figure 3-25: Angle connections employed in Octavio's and Pascual's module (Octavio &

Pascual, 2009).


General

Octavio and Pascual have designed a simple yet effective modular system concept.

The concept has yet to be built and placed under real world tests. However, Octavio

and Pascual have completed extensive analysis of the entire concept from designing to

manufacturing and construction on site.

Construction and Quality Review

Overall, Octavio’s and Pascual’s modular system design is reasonably easy to

construct. The arrangement of the various sections, sheeting, boards, insulation and


weather proofing follow standard arrangements seen in traditional construction. The

simple bolt-on angle connections provide sufficient strength whilst keeping the

assembly of these members easy.

The greatest downfall in terms of constructability of the modules, is the inclusion of

welded connections. Welded connections have been employed in the joining of the

main beams to the main columns of the module chassis. The welded connections are

costly and significant time is required to assemble them.

Octavio and Pascual selected to utilise CFS for most structural members. The resulting

product is a lightweight and structurally adequate system. The selection of CFS

profiles is limited to C-profile, Edge profile and Angle profile sections. All three of

these sections are considered first generation CFS products. Newer generations of CFS

products provide more benefits including improved structural capacity, lower weight

and easy fabrication.

Octavio and Pascual have neglected to address and incorporate measures for probable

construction tolerance issues. The bolt connections between the main column, primary

roof beam, primary floor beam and module-to-module connections have not been

designed to permit any construction tolerances. Poor alignment of the complete

structure could result as seen in the 461 Dean project. Appropriately designed match

plates should be incorporated to address the construction tolerance issues.

3.4.5 Conclusion

Octavio and Pascual have developed a simple yet effective modular building design.

The structural scheme of Octavio’s and Pascual’s modules incorporated mostly steel

members with a majority being CFS. The few HRS were employed to form a rigid

module chassis as the main structural load members.

The minimal design of the angle connections is easy to install though an adjustment to

the design should be made to address alignment issues. The welded connections of the

module provided the strength necessary to facilitate the structural loading though the

downfall is the considerable time and costs to assemble the welds.

Overall, Octavio’s and Pascual’s modular building system design is suitable for low

load applications such as their intended low-rise student accommodation apartment.

To construct a taller system, Octavio and Pascual would need to incorporate more

bracing mechanisms such as a central structural core system.


3.5 THE VERBUS SYSTEM

3.5.1 General

The Verbus System, also known as V System, is a patented MBS consisting of a steel

monocoque shell and special column to column connections. The patent was

developed by Verbus Limited, whom is now owned by CIMC MBS (China

International Marine Containers Modular Building Systems). CIMC MBS is a major

provider of MBSs who are headquartered in Jiangmen, China with regional offices in

both Europe and Australia. Patent details of the Verbus System are presented in Table

3-20. The Verbus System is CIMC MBS’s flagship product and is has been attributed

to the completion of numerous modular building projects.

Table 3-20: Patent details of the Verbus System.

Patent Title: Building Modules

Patent No. (US): US 2007/0271857 A1

Date of Patent (US): Nov. 29, 2007

Patent No. (WIPO): WO 2005038155A1

Inventor:

David Heather, Buckinghamshire (GB); Collin Ewart Harding,

Bournemouth (GB); Rufus Harold Harding, Wiltshire (GB);

Roderick MacDonald, London (GB); Richard Clive Ogden,

Buckinghamshire (GB)

Assignee: Verbus Limited, Bournemouth (GB)


Module Chassis

The structural scheme of the Verbus System is essentially a monocoque shell, namely

structural loading is supported through the external skin; for the Verbus System this

means the loads are shared between the chassis as well as the are the wall, floor and

roof systems of the modules. The Verbus System and a complete overview of its design

features is depicted in Figure 3-26. The chassis of the Verbus System consists of four

horizontal side rails, four horizontal end rails and four vertical posts, all open steel

sections. Corrugated steel sheets are connected to these rails via welded connections.

The wall, floor and ceiling systems of the Verbus System prescribe two main

components; elongated members and metal panels. Together with the chassis, these

components bear the structural loading imposed on the module. The patent for the

Verbus System expresses that it is preferable that the elongated members are composed

of steel and take the form of open or hollow sections.


Figure 3-26: Overview of the module structural scheme of the Verbus System (Verbus Systems,

2009).

Wall System

The wall system configuration, presented in Figure 3-27, consists of five main

elements; steel panels, steel studding, insulation, plywood board and plasterboards.

Further details of the Verbus wall system is presented in Table 3-21.

Figure 3-27: Example internal wall construction of the Verbus System (Heather, Harding,

Harding, MacDonald, & Ogden, 2007).


Table 3-21: Details of the wall system profile of Verbus Systems’ module design.


Wall Column CFS L-Shape Studs

Wall Lining (Primary) Plywood 9mm

Wall Lining (Secondary) Plasterboard 12.5mm x 2

Insulation Insulation Boards 40mm

Outer Shell Corten Steel Sheet 1.6mm

Steel studding of L-shaped CFS sections form the main vertical members and are

connected to the interior of the steel panels via stitch welding. The L-shaped profile of

the steel studs allows for insulation boards to be slotted through and securely held in

placed. Plywood boards overlay the insulation boards and are attached to the steel

studding.

Roof System

The roof system configuration, best presented in Figure 3-26, consists of five main

elements; steel panels, steel studding, insulation, plywood board and plasterboards.

Further details of the Verbus roof system is presented in Table 3-22.

Table 3-22: Details of the roof system profile of Verbus Systems’ module design.


Roof Joist CFS C-Sections

Ceiling Board (Primary) Plywood 9mm

Ceiling Board (Secondary) Plasterboard 12.5mm x 2



The arrangement of the roof system follows that roof joists in the form of C-sections

are attached to the Corten steel sheet that forms the outer shell. Slotted between the

roof joists are insulation boards. Attached to the lower face of the joists is plywood

followed two layers of plasterboard.

Floor System

The example floor construction from the patent is presented in Figure 3-28. It consists

of four main elements; steel panels, steel studding, insulation and plywood boards.

Further details of the Verbus floor system is presented in Table 3-23.


Figure 3-28: Example floor construction of the Verbus System (Heather et al., 2007).

Floor joists in the form of C-sections are attached to the corrugated steel panel. Within

the confined volume of adjacent floor joists, insulation boards are slotted through.

Overlying the floor joists and insulation boards is a plywood layer.

Table 3-23: Details of the floor system profile of Verbus Systems’ module design.


Floor Joist CFS C-Sections

Floor Board Plywood 28mm



Connections - General

The connection elements in the Verbus System are a key component in the success of

Verbus System being a practical and effective modular building system. The

connection elements provided in the Verbus System have been designed generally in

accordance of ISO/TC-104-1161 (ISO/TC 104 Freight Containers), the same

connection elements found in the designs of conventional freight containers.

Connections - Corner Castings

Corner castings are the primary connection elements in the Verbus System. As the

name suggests, these elements are found in the corner of the modules. A spacing of

2259 mm centre-to-centre between the corner castings is adopted; in doing so, allows

the system to be hoisted and transported with conventional freight container load

handling equipment. Figure 3-29 shows an explode view of four corner castings and

the various elements forming them. Figure 3-30 shows the same four corner castings

in an assembled form.


Figure 3-29: Exploded view of corner castings (Heather et al., 2007).

Figure 3-30: Assembled corner castings (Heather et al., 2007).

As seen in Figure 3-29 and Figure 3-30, a simple position then lock mechanism is used

to join adjacent modules. Lugs (83) are guided into position to slot through the

apertures of the hollow constructed corner castings (21). Gaskets (85 and 87) form the

protective sealing between these elements, preventing exposure to the elements,

accommodating contraction and expansion of the modules, relieving stresses and

minimizing acoustic vibration. Once all in place, bolts (92) are fed through washers

(93), through the lock down plates (88) which pierce the corner castings and finally

fastened through the threaded holes (91) of their respective lugs. Essentially, the bolts

and lock down plates maintain the vertical connection and the lugs and plate part

maintain the horizontal connection.


Connections - Intermediate Castings

Intermediate castings, like those of the corner castings, are placed at intermediate

intervals between the corner castings as seen in Figure 3-31. These extra castings are

positioned on opposite ends of the module, at a centre-to-centre spacing of 2259 mm

and at both top and bottoms railings. The role of these extra castings is to allow the

module to be fastened to standard fasteners on a heavy vehicle trailer whilst hoisted

by standard lifting equipment. Given their position (i.e. not at the corners), these extra

castings have less apertures than the corner castings.

Figure 3-31: Hoisting process of the Verbus System (Heather et al., 2007).


General

The steel monocoque shell adopted in the Verbus System is a structurally efficient

design. The system provides adequate structural capacity with minimal materials. CFS

sections provide the required strength to withstand the structural loading at minimal

weight. Utilising steel panels provide adequate lateral capacity without the need for

multiple connections and thus reducing fabrication efforts.


Verbus System’s module is a simple to construct yet effective module design. The use

of CFS sections and other lightweight materials permits the modules to be reasonably

easy to assemble and transport. Incorporating an all-steel frame allows welding to be


utilised as the sole connection method within the modules. Although, by employing

welded connections the costs and manufacturing times are increased.

The Verbus System has chosen to make high use of the same ISO corner casting seen

on conventional freight containers. This design feature is very practical, as it reduces

the need to develop new technologies to hoist and transport the modules. Although, a

major downfall of the connection is that its assembly requires the workers to be outside

of the module and exposed to heights and the elements. In addition, the connection

lacks the necessary features to address tolerance issues and hence, must be perfectly

aligned for the connection to be assembled.

3.5.4 Conclusion

The Verbus System has managed to address many of the issues facing modular

construction. Employing a monocoque shell design has resulted in a light-weight as

well as structurally adequate modular building system. Utilizing CFS members in the

chassis and roof, floor and wall systems contributed largely to the low weight – high

strength design. By selecting L-shaped steel studding, insulation boards are simply

slotted between the closed cavities created.

The disadvantage exhibited in the monocoque shell design of the Verbus System is the

utilisation of welded connections for the join between the steel panels to steel rails and

steel panels to L-shaped steel studding. Employing welded connections results in

slower assembly times and increased associated costs.

The innovative implementation of the corner castings into the Verbus System has

provided a module-to-module connection that appropriately addresses alignment

issues and minimizes on site construction efforts such as on-site assembly time. The

corner castings adopt the form of a standard shipping container casting, permitting the

modules to be transported and hoisted by current technologies without the need for

any modifications or adjustments. The drawback of the corner casting is the

requirement to be outside of the module when assembling the connection; this draws

safety concerns for on-site installation.

The Verbus System by CIMC is a well-rounded module design. The system

incorporates elements that address many shortcomings seen in other systems such as

structural efficiency (weight-to-strength ratio), ease of construction and transportation.

The only notable fault is the concern for safety when installing the connections.


3.6 DOUBLE SKIN STEEL PANEL WALL SYSTEM

3.6.1 General

Full-scale experimental testing of framed MBSs with double skin steel panel wall

systems was performed by researchers in a cooperative study between the Seoul

National University, Ajou University, the Steel Structure Research Laboratory of the

Republic of Korea and the University of California. The study aimed to improve

modular construction quality by developing a lateral load resisting system alternative

to steel shear walls and insitu concrete walls. Steel shear walls are common and

effective lateral load resisting systems in modular systems. Although, they are

typically expensive due to the volume of material required, number of welding

connections needed and are not easily able to incorporate openings such as doors or

walkways. Similarly, insitu concrete walls are common and effect lateral load resisting

systems; however, due to the time required for concrete to cure and its weight, it is not

suitable for modular construction purposes.

The study proposed a steel panel wall system and investigated the structural behaviour

of the unique configuration, particularly its performance as a lateral resisting system.

A double (back-to-back) steel panel system is also investigated. The study then

investigated the application of these wall systems to framed modular steel systems.

3.6.2 Test Specimen Details

Double Skin Steel Panel Wall System

The double skin steel panel wall system consists of a 0.7 mm thick corrugated steel

panel sandwich on both sides by 2 mm thick flat steel panels. Further profile details of

the steel panel can be viewed in Figure 3-32. Material properties of the steel used in

the double skin steel panel can be viewed in Table 3-24. The corrugated steel panel is

attached to the flat steel panels by means of soldering, an uncommon method of

structural steel connection. Soldering was employed to ensure even surface contact of

the corrugated panel. Soldering was also considered a more economical alternative to

welding. Four double skin steel panel configurations were tested. Details of their

configurations are presented in Table 3-25. Three base configured specimens with

varying widths were tested. To investigate the behaviour between independent panels

a fourth specimen (LSP-400D), consisting of a double panel configuration and is

depicted in Figure 3-33, was tested.


Double Steel Plates 0.7mm Corrugated Core

Soldering Connection

Figure 3-32: Double skin steel panels with insulation (specimen LSP-400S) (Hong et al., 2011).

Figure 3-33: Double panel configuration of the double skin steel panel (specimen LSP-400D)

(Hong et al., 2011).

Table 3-24: Material properties of the steel in the double skin steel panel (Hong et al., 2011).

Product Name,

Description

Modulus of

Elasticity, E

(GPa)

Yield

Strength σy

(MPa)

Tensile

Strength σu

(MPa)

Elongation at

Rupture ϵu

(%)

Material

Overstrength

Factor

SS400, t = 0.7

mm 210 259 432 39 1.10

SS400, t = 2 mm 213 258 412 37 1.10

SPH-A, t =

4.5mm 208 376 488 35 1.28

Table 3-25: Double skin steel panel test specimen configurations (Hong et al., 2011).

Specimen Double Skin Steel Panel

Wall Type Width of Steel Plate, b (mm) Slenderness Ratio

LSP-400S 400 6 Unit Panel



LSP-400D 400 6 Double Panel

Framed Modular System

The framed modular system followed a simple and standard design as depicted in

Figure 3-34. In each module unit, a floor system composed of MCO 330-12-7 beams

formed the foundation from which upon four columns of HSS 125-125-4.5 profile

supported a ceiling composed of four MCO 200-120-4.5 beams. Each unit module

measured 6 m long by 3 m wide by 3 m high. The profile of the MCO (Modular

Construction Optimized) beam is shown in Figure 3-35 with geometric details

presented in Table 3-26.


Three variations of the framed modular system were tested; a one storey bare system

(M1F), a two-storey bare system (M2F) and a two-storey system incorporating the

double skin steel panel wall systems (M2F-SP). M1F was used determine the structural

performance of a single storey bare module unit. M2F was used to determine the

structural performance of a two-storey bare module system. M2F-SP was used to

determine the structural performance of a two-storey module system with additional

lateral reinforcement by inclusion of the double skin steel panel wall systems. The

double skin steel panel wall systems were placed in pairs in the longitudinal walls of

the two-storey modular system. This specimen arrangement was tested to investigate

the interaction behaviour between the steel panels and the modular frame.

Figure 3-34: Framed modular system MF1 (Hong et al., 2011).

Figure 3-35: Profile of the MCO beam (Hong et al., 2011).

Table 3-26: Section details of the MCO beam (Hong et al., 2011).

Section Height

(mm)

Flange Width

(mm)

Thickness of

Steel (mm)

Sectional

Area (cm2)

Second

Moment of

Area (cm4)

MCO 200-120-4.5 200 120 4.5 30.1 1529.66

MCO 330-120-7 300 120 7 55.64 8519.86

3.6.3 Test Details

Two types of experimental testing were executed; the first, to investigate the individual

capacities of the double skin steel panel wall systems and the other to investigate the


interaction behaviour of these panels when used in a modular frame system. The

testing apparatus was designed to allow longitudinal displacement and prevent

transverse displacement of the loading beam. Monotonic loading was applied with use

of an actuator, mimicking story drift conditions. Loading was applied three times at

each drift angle, R (1/500, 1/250, 1/100, 1/50). The resulting story drift and the external

steel plate strain were monitored using linear variable differential transformers.

3.6.4 Results and Review

The slender double skin steel panel wall systems were found to follow the theoretical

flexural behaviour of steel plates – single wall hysteresis. All specimens displayed

large initial stiffness. Connection failure between the internal corrugated sheet and the

external flat sheets initiated the onset of local buckling in the external sheets, resulting

in specific yield lines. Strength degradation would occur after initiation of transverse

deformations. Thus, the connection between the internal corrugate sheet and external

flat sheets by means of soldering was found to be effective in preventing early

unintended failure of the panels.

The study concludes that the proposed double skin steel panel wall system is an

effective supplementary lateral load resisting structure. Implementation of the panel

system in a modular frame system increased the lateral load resisting capacity by four

folds and also significantly increased the initial lateral stiffness of the system. Failure

occurred in the double skin steel panel wall systems before failure of the module’s

mainframe and hence, allows for control of severe damage to the chassis of the module.

3.6.5 Conclusion

The proposed double skin steel panel wall system has been proven to be an effective

supplementary lateral load resisting system for application in framed modular systems.

The double skin steel panel wall systems show moderate ductility with favourable

energy dissipation due to their post buckling strength. In comparison to steel shear

walls, these panel systems are cheaper, lighter and easier to manufacture. The steel

panels design also allows for openings and voids to be implemented and inclusion of

thermal insulation material, unlike steel shear walls. The greatest disadvantage shown

in these wall systems is the employment of soldered connections. Although soldering

is cheaper than welding, it is still time consuming to assemble.


3.7 VECTORBLOC CONNECTION SYSTEM

3.7.1 General

The VectorBloc Connection System is connection system specifically designed for

modular building applications. The VectorBloc Connection System itself is a part of a

larger collective of products, systems and concepts aimed at improving and

overcoming various drawbacks of modular construction including issues surrounding

accumulating tolerances, voids, difficult hoisting procedures and hazardous work

under suspended loads. This collective is called the VectorBloc Standardized Modular

Building System and was developed by Vector Praxis who is headed by Julian Bowron

of Toronto, Canada. Vector Praxis (2015), claims their VectorBloc:

• Allows for modules of any size;

• Provides sufficient scalable vertical tension and gravity capacity;

• Assembles safely from inside the module;

• Provides accessory connection points or connecting balconies, floors and

façade cassettes; and

• Does not rely on continuous walls for structural stability.

This review will examine both the corner and double connection (cruciform

connection for adjacent modules). Figure 3-36 shows the VectorBloc Corner

Connection System (a) and VectorBloc Double Connection System (b). Patent details

of the VectorBloc Connection System are presented in Table 3-27.

Figure 3-36: VectorBloc Connection Systems (Vector Praxis, 2016).


Table 3-27: Patent details of the VectorBloc Connection System.

Patent Title: Structural Modular Building Connector

Patent No. (US): US9845595B2

Date of Patent (US): 19/12/2017

Inventor: Julian Bowron

Assignee: Julian Bowron

3.7.2 Structural Details

The VectorBloc Connection System was inspired by the Malcom McLean’s ISO

Corner System, a design feature of modern freight and shipping containers. Building

upon McLean’s concept, Vector Praxis developed several features making the system

more suitable for application in modular buildings. Vector Praxis has introduced both

standard and customizable VectorBloc systems to suit the needs of the building

arrangement and other building design features. Only the standard design will be

discussed herein. Figure 3-37 shows exploded views of the standard VectorBloc

Corner Connection System (a) and the standard VectorBloc Double Connection

System (b).

Figure 3-37: Vector Praxis’s standard VectorBloc Systems (Vector Praxis, 2015).

The VectorBloc Connection system comprises of five key components, they are:

• Tension bolts, Figure 3-38(a);

• The lower VectorBloc connector, Figure 3-38(b);

• Gusset plate screws, Figure 3-38(c);

• The gusset plate, Figure 3-38(d); and,

• The upper VectorBloc connector, Figure 3-38(e).


Figure 3-38: Assembly of the VectorBloc Connection System (Bowron, Gulliford, Churchill,

Cerone, & Mallie, 2014).

As per Figure 3-38, the assembly of the VectorBloc Connection system is simply a

gusset plate sandwiched by upper and lower connector bodies via the fastening of bolts

and screws. Both upper and lower connectors are load bearing hollow bodied elements,

made from an unspecified weldable steel alloy. The connectors resemble a

quadrilateral (square-like) cross-section with extruding arms. Bevelled edges are

implemented in the design of the connectors to help guide the alignment of connecting

elements. For the lower connector, the top end receives the vertical corner member of

the module and the bottom end receives the gusset plate. For the upper connector, the

top end receives the gusset plate and the bottom end receives the vertical corner

member of the module. Joining of the connectors to their respective vertical and

horizontal module chassis members is completed by welding. Welding allows a

moment connection to be formed.

The extruding arms of the connection system provide a passage for the fastening of

bolts and contribute to compression and tension capacity of blocks. The holes in corner

blocks provide a means of connection to tie downs and hoisting devices for the

installation of the module.

The gusset plate forms the interposed element between the upper and lower connector

bodies serving mainly as a horizontal connection element for the corner connection

system. To facilitate the double connection system, the gusset plate is enlarged to

interpose between the upper and lower connectors as well as adjacent connectors. On


the top face of the gusset plate exist tapered pins extruding upwards. In combination

with the recesses on the underside of a connector block, an effective and simple means

of alignment is achieved for directing the descending modules in place.

Tension bolts are used to connect and fasten together the sandwiched assembly. The

bolts are accessible within the wall cavities. Passing the tension bolts through the upper

and lower blocks provides vertical structural continuity between the modules, forming

a robust vertical connection system. Passing the tension bolts through the gusset plate

provides horizontal structural continuity through the floors of the modules, forming a

robust horizontal connection system.

3.7.3 Review

The VectorBloc Connection System is an effective and appropriately design

connection system for use in MBSs. This connection system design ensures that

adequate structural capacities can be achieved. In addition, the design appropriately

addresses alignment issues by using extruding tapered pins. These tapered pins guide

the connector blocks and gusset plate into place. The design also allows the user to

assemble the connection from inside the module when connecting modules together

on site. This reduces the risks of on-site safety concerns. The drawback of the design

is the welding connections that are utilised. Although, through employing welded

connections, moment connections are effectively formed.

3.7.4 Conclusion

Vector Praxis has developed an innovative and highly effective connection system for

use in MBSs. Their intention is to introduce a standard connection design for the

assembly of module in modular buildings, analogous to that of the ISO Corner System

seen on all modern freight and shipping containers. The VectorBloc Connection

System has demonstrated to be cheap, safe and easy to install while providing adequate

structural performance. The system also provides accessory connection points to

accommodate architectural design options such as balconies, floors and façades.

The VectorBloc Connection System is a developing design with patents currently

being revised to incorporate amendments. Already, the VectorBloc Connection

System has been employed in real-life, multi-storey, modular building projects.


3.8 CONNECTOR SYSTEM FOR BUILDING MODULES BY VERBUS

SYSTEMS

3.8.1 General

An improved connector system for building modules has been developed and patented

by Verbus Systems Limited. Building upon their previous connector system, presented

in patent WO 2005038155A1, the connector system offers greater flexibility in design

and module arrangement as well as being more economical to produce and execute.

The updated connector system retains its ISO/TC 104 compatibility to continue

allowing conventional freight container handling equipment to interact with the

connection. Patent details of the new connector system are presented in Table 3-28.

Table 3-28: Patent details of the Connector System for Building Modules.

Patent Title: Connector System for Building Modules

Patent No. (US): US 8,549,796, B2

Date of Patent (US): Oct. 8, 2013

Patent No. (WIPO): WO 2008107693A1

Inventor: David Heather, High Wycombe (GB)

Assignee: Verbus International Limited, London (GB)

3.8.2 Structural Details

Verbus Systems’ connector system utilises a guided vertical system to initiate the

alignment and connection. The assembled connector system is shown in Figure 3-39.

The connector system comprises of numerous elements as shown Figure 3-40.

Essentially, the mechanism of the connection follows as spigots (61) preventing

horizontal movement and a fastening system preventing vertical translation. The

spigots (61) also facilitate the alignment with their tapering profiles.

Figure 3-39: Assembled improved connector system (Heather, 2012).


Figure 3-40: Exploded view of the improved connector system (Heather, 2012).

Establishing structural continuity in the connector system begins with laying the lower

modules alongside each other so that the position of their respective upper connector

blocks (51 and 52) is positioned as shown in Figure 3-40. Gaskets (64), which alleviate

stresses from contraction and expansion of the modules, are placed on the connector

blocks (51 and 52) in alignment with their respective connector block spigot openings

(58). The spigots (61) are inserted into the gasket (64) and spigot openings (58)

resulting in the first portions of the spigots (72) forming a tight fitting with the spigot

openings (58). A fixing plate (63) is installed over the top of the upper ends of the

spigot and rests on top of the gaskets (64). Additional gaskets (64) are then installed

over the top of the spigots (61) followed by lowering of the upper modules and their

lower connector blocks (53, 54) to fit on top of the spigots (61) and additional gaskets

(64), thus completing structural continuity of the connection.

Next, a vertical fastening set is employed to secure the connector blocks together. The

set consists of designations 65, 66, 67 and 68. The procedure begins with inserting the

bolt (66) and washer (68) into the slot (60) of the connector blocks (51, 52, 53 and 54).

A spacer plate (65) is fitted between the upper and lower connector blocks with its

cutaway encircling the bolt (66). A nut (67) is then used to fasten the system together,

thus completing the fastening and securing of the connector system.


The inclusion of the fixing plate has opened an array of design options for the

connection. The fixing plate can be altered in form, profile and dimensions as well as

incorporate attached elements, so as long as the openings in the fixing plate remain, a

secured connection is maintained. In the given example figures (Figure 3-41 - Figure

3-45), the fixing plate has been altered to present different design options.

From Figure 3-41, a horizontal ledge has been incorporated into the fixing plate. The

ledge could be used to provide an attachment point, for example brick cladding. From

Figure 3-42, a vertical plate with holes has been incorporated into the fixing plate. The

pate could be used to provide an attachment point, for example façade elements. From

Figure 3-43, the length of the fixing plate has been extended. This allows for spacing

to exist between connected modules. Further extending the fixing plate, as in Figure

3-44, provides significantly more spacing and by incorporating an I-beam design on

the fixing plate between the modules results in substantially more strength in the fixing

plate to allow another system to be supported, for example a corridor. Extrusion of the

fixing plate can occur in both longitudinal and lateral directions as seen in Figure 3-45.

Figure 3-41: A horizontal ledge incorporated in the fixing plate (Heather, 2012).

Figure 3-42: A vertical plate incorporated in the fixing plate (Heather, 2012).


e

Figure 3-43: Extension of the fixing plate between connector blocks (Heather, 2012).

Figure 3-44: Further extension of the fixing plate between connector blocks (Heather, 2012).

Figure 3-45: Lateral extrusion of the fixing plate (Heather, 2012).

3.8.3 Review

The updated connector system has had several changes made with significant

improvements seen in economy, ease of use and more design options; so significant,

that the Verbus System now adopts the updated connector system in favour of the

original design.


Spigots (61) are introduced to the connection, essentially substituting to the lugs of the

older design. The major difference between the two, is that the spigots are separated

into two components allowing their location to vary. In addition, the increased tapering

in the ends of the spigot further eases the alignment procedure for the modules.

The updated connector system includes a new feature to allow for tolerance in the

alignment of modules. This feature is seen in the slot (60) and plate (65), where the

cutaway of these elements allows the bolt and nut to be fastened even if a minor

tolerance exists in the direction of the cutaways.

Attributing to the improvements is the inclusion of a fixing plate (63). The fixing plate

provides the needed horizontal structural continuity in the connection as well as

opening a wide range of design options. This is due to the adaptable and variable

design of the fixing plate; the fixing plate can be extruded, altered in form and can

accommodate additional elements. Although in manipulating the design of the fixing

plate, the resultant is a greater likelihood of increasing stress and altering its

distribution throughout the fixing plate and overall connector system.

With the addition of these new elements, it is evident that more material is needed to

manufacture the connector system and greater fabrication efforts are required. The

updated connector system still needs to be assembled from outside the modules,

introducing greater risk to the labourers who do so. The first set of lower modules will

also need to be placed with absolute precision to allow the spigot to pierce through the

fixing plate and aperture in the connector block.

3.8.4 Conclusion

The Connector System for Building Modules by Verbus Systems is an improved

connection system for application in MBSs. The system adequately provides sufficient

structural capacity to allow multi-storey modular buildings to be constructed. The

design features components that allows various architectural features to be connected

to the system such as brick cladding. The connection system also features improved

measures to address alignment issues. The downfall of the design is greater volume of

material and increased efforts to fabricate the various components of the connection

system. In addition, to minimize alignment issues, the first set of lower modules must

be placed with absolute precision to allow the connector system to be utilized

effectively.


3.9 CONCLUSION

This chapter has presented several case studies to highlight current advances in the

modular construction industry. The case studies have discussed the advantages and

drawbacks that each system has and their relevancy of application in MBSs. Four

complete MBSs were reviewed, these projects were: 461 Dean of New York City,

SOHO Apartments of Darwin, Octavio’s and Pascual’s Affordable Steel Concept and

the Verbus System.

461 Dean is currently the world’s tallest modular constructed building achieving

sufficient strength in its design to attain this title. The project was supposed to

demonstrate the capabilities of modular construction, though construction tolerance

issues were prevalent and caused the project to be severely delayed.

SOHO Apartments of Darwin is Australia’s tallest constructed modular building. The

structure sits upon a podium and employs integrated precast and insitu concrete

elements with steel elements to achieve the required structural strength. Using insitu

concrete elements delays the construction process (due to the required curing period),

but the designers were able to develop a construction process that minimized the delay.

Octavio and Pascual developed a modular building system concept for their

postgraduate studies. Their design kept costs to a minimum through simplifying their

design and adopting economical and sustainable measures. However, the simplified

design lacked measures for addressing construction tolerance issues and provisions for

multi-storey arrangements.

CIMC developed the patented Verbus System to address several shortcomings of

modular construction. Their design follows a monocoque shell incorporating

lightweight elements in structurally efficient configurations. Corner castings like those

seen in standard shipping containers were adopted for module-to-module connections.

This avoided the need to develop new technologies to lift, hoist and transport the

modules.

In addition to the case studies performed on complete MBSs, a further three case

studies were performed on the latest engineering developments in the modular

construction field. These case studies demonstrate the developments in progress to

address the shortcomings of MBSs. These case studies examined: two connections

systems and a wall system all specific to MBS.


Chapter 4: Thermal Modelling of Light

Gauge Steel Framed Wall

Systems Proposed for Modular

Building Systems

4.1 INTRODUCTION

The tragic Grenfell Tower fire incident of June 2017 saw 20 out of 24 floors consumed

by fire within 30 minutes. Several design flaws and maintenance procedures

contributed to the rapid spread of fire, though the main contributing factor is said to be

the combustible exterior metal composite material (MCM) panels (Gaut, 2018). The

arrangement of an MCM panel follows a solid plastic core enclosed by an outer layer

of metal skin on each side. The Grenfell Tower fire incident sparked building and

construction statutory bodies to review their standards around the design of multi-

storey buildings and fire safety, specifically that of steel frame buildings and steel wall

panel systems.

Figure 4-1: The Grenfell Tower fire incident of June, 2017 (Dame Judith, 2018).

Cold-formed light-gauge steel frame (LSF) wall systems (see Figure 4-2) are

becoming increasing implemented into the structural designs of many MBSs. These

advanced steel wall panel systems are often incorporated in MBSs due to their

numerous benefits. The benefits include providing an efficient (weight-to-strength

ratio) load-bearing system, increased speed of construction, improved performance

characteristics and greater level of manufacturing control and geometric accuracy.

These wall systems can be used in both single or multi-storey structures. The standard


LSF wall system configuration comprises of a light-weight steel frame, wall lining that

encloses the wall and insulation within the cavities created by the wall lining.

Figure 4-2: LSF Wall System (Vardakoulias, 2015).

As highlighted previously, the fire performance of multi-storey buildings especially

those of steel frames and steel wall panel systems is a significant parameter to consider.

Most MBS are composed of steel frames with steel wall panel systems. In the case of

fire, the designer must devise measures to limit the passage of fire and delay its

movement and spread rates. If fire spreads to the steel frame elements, catastrophic

collapse of the entire building can occur by degradation of the steel frame.

For steel MBS, the passage of fire can be delayed with the incorporation of fire-

insulative materials in the wall systems. For standard LSF wall systems, single or

multiple layers of fire rated plasterboards (commonly gypsum plasterboard) are

attached to the steel studs and depending on the building requirements, cavity

insulation may be used to improve the thermal and acoustic performances of the

system.

Thermal insulation is an important design component of a building as it stipulates the

structural performance of the building as well as the comfort levels of the occupants

within the building. Thermal insulative materials such as rockwool are frequently used

to infill the cavities of LSF wall and MBSs. The implementation of the thermal

insulative materials results in lowering heat loss of and through the system.

Interestingly though, implementing thermal insulative materials (rockwool, cellulose

and glass fibre) in the cavities of LSF wall systems also have detrimental effects on

the structural performance of the systems (Gunalan et al., 2013). This is due to the

significantly lower thermal conductivity of the insulation material when compared to


the adjacent steel members in the cavities of the systems. They found that the cavity

insulating materials channels the heat along and through the steel studs resulting in a

non-uniform temperature distribution of the steel studs.

To thoroughly understand the fire performance and heat transfer behaviours of LSF

wall systems, full-scale fire tests should be undertaken. However, these tests are

extremely expensive, labour demanding and time consuming, and thus an alternative

method is needed. Thermal modelling offers an effective, inexpensive and timely

approach to understanding these behaviours.

Rusthi et al. (2017) performs thermal modelling of LSF wall systems by developing

three dimensional (3D) finite elements (FE) models using ABAQUS CAE to

investigate the fire performance and heat transfer of existing LSF wall system

configurations. They utilised eight node linear heat transfer brick elements (DC3D8)

with solid-solid heat transfer through elements in their model. Rusthi et al. (2017)

showed the developed FE models were able to accurately predict the heat transfer for

load-bearing LSF wall configurations.

The Grenfell Tower fire incident has incited building authorities to review their

understanding, standards and guidelines on the design of multistorey steel buildings

particularly those incorporating steel wall panel systems. This chapter introduces

improved LSF wall system configurations that have been developed for integration in

this study’s proposed MBS design that also includes innovative measures to improve

their fire performance. The thermal behaviour of the LSF wall system configurations

are modelled with FE software and a discussion on the results is presented.

4.2 INNOVATIVE LSF WALL SYSTEM CONFIGURATIONS

To improve the fire performance of LSF wall systems and to lessen the detrimental

effect that cavity insulation has on the CFS studs, three innovative LSF walls systems

are proposed. For comparative purposes, these three systems are evaluated against two

standard systems. Optimum non-load bearing LSF wall configurations have been

considered based on fire tests conducted by Dias et al. (2017) and Rusthi et al. (2017).

The configurations of the LSF wall systems proposed for analysis in this study are

discussed in this section. Table 4-1 presents details of the test specimen configurations.


Table 4-1: Details of the test specimen configurations.

Test

Specimen

No. Configuration Description

1

LSF wall system made with double layer

gypsum plasterboard on each side, SCS

studs and full cavity insulation.

2



studs.

3



studs and discontinuous cavity insulation.

4



studs and back blocking gypsum

plasterboard on each side of the studs.

5



studs, back blocking gypsum plasterboard

on each side of the studs and

discontinuous cavity insulation.

Configuration 1 – Standard LSF Wall System with Full Cavity Insulation

Configuration 1 is a standard LSF wall system with full cavity insulation. Stiffened

channel sections form the wall studs and the system is enclosed by a double layer of

gypsum plasterboard on each side of the wall system (internal and external walls). The

cavity of the wall system is completely occupied by insulation. This configuration shall

be referred to as the standard LSF wall system configuration and is shown as Test

Specimen 1 in Table 4-1.

Configuration 2 – Standard LSF Wall System with no Cavity Insulation

Configuration 2 is a standard LSF wall system with unoccupied cavities (no insulation

present). The wall studs consist of stiffened channel section members. A double layer

of gypsum plasterboard is attached to each flange of the wall stud members and thus


enclosing the wall system and creating cavities. No materials occupy the cavities. It is

predicted that the absence of cavity insulation will result in a more uniform

temperature distribution along the wall studs and thus increase the performance of the

wall system. Configuration 2 is presented as Test Specimen 2 in Table 4-1.

Configuration 3 – Innovative LSF Wall System with Discontinuous Cavity

Insulation

Configuration 3 is built upon Configuration 1 with a discontinuous arrangement of

cavity insulation is employed. The configuration follows the standard configuration of

stiffened channel sections as the wall studs and a double layer of gypsum plasterboard

on each flange of the wall studs to enclose the wall system. Within the cavities of the

wall system insulation is inserted, though a void of 100mm around the wall stud is left

and hence, a discontinuous path of insulation is formed. The break in insulation

material is expected to disrupt the flow of heat transfer and thus encourage uniform

temperature distribution along the wall stud. Configuration 3 is presented in Table 4-1

as Test Specimen 3.

Configuration 4 – Innovative LSF Wall System with Back-Blocking Board

Configuration 4 is built upon Configuration 2 with the addition of a layer of gypsum

plasterboard is incorporated in a back-blocking like arrangement. Rusthi et al. (2017)

showed that provision of an additional plasterboard strip, usually of 100mm width,

vertically along the stud surface was found to delay the stud temperature rise.

Configuration 4 is formed with stiffened channel sections as the wall studs and a

double layer of gypsum plasterboard on both sides of the wall system (internal and

external walls). No cavity insulation is incorporated. An additional layer of gypsum

plasterboard with a width slightly greater than the flanges of the stiffened channel

section is attached between the wall stud and the double layer of gypsum plasterboard

wall lining. Incorporating this extra layer of gypsum plasterboard effectively lengthens

the heat transfer travel path resulting in greater fire resistance performance.

Limiting the width of the new layer of gypsum plasterboard to not span the full width

of the wall, reduces the volume of material used whilst still providing the benefits from

increasing the length of the heat transfer travel path. Configuration 4 is seen as Test

Specimen 4 in Table 4-1.


Configuration 5 – Innovative LSF Wall System with Discontinuous Cavity

Insulation and Back-Blocking Board

Configuration 5 is built upon the combination of Configurations 3 and 4. Like all

previously presented configurations, Configuration 5 consists of stiffened channel

sections as the wall studs and a double layer of gypsum plasterboard on each side of

the wall system (internal and external walls). The discontinuous cavity arrangement of

Configuration 3 is employed and incorporated with the back-blocking gypsum

plasterboard arrangement of Configuration 4. Configuration 5 is expected to exceed

the performance of all the other configurations as the configuration provides both

uniform temperature distribution along the wall studs and increase length of the heat

transfer travel path. Configuration 5 is presented in Table 4-1 as Test Specimen 5.

4.3 THERMAL PROPERTIES

To be able to numerically model LSF wall systems and simulate the heat transfer

through the configurations, the corresponding material thermal properties at elevated

temperatures are required. Theses thermal properties include specific heat, relative

density and thermal conductivity for temperatures up to 1200ºC and are used as inputs

within the finite element heat transfer models. This section summarises the applied

thermal properties for gypsum plasterboard, rockwool insulation and steel used in the

thermal analyses and ABAQUS CAE.

4.3.1 Gypsum Plasterboard

Gypsum plasterboard was chosen as the fire protective wall boards in all developed

FE models in this study. The thermal properties of gypsum plasterboard including

specific heat, relative density and thermal conductivity was derived from the data

presented by Keerthan and Mahendran (2012a) for temperatures up to 1200ºC. Figure

4-3 (a) (b) and (c) show the proposed values as a function of temperature.

The thermal conductivity for the gypsum plasterboards was modified to account for

the effect of ablation and moisture movement. Figure 4-3 (a) shows the modified

thermal conductivity of gypsum plasterboard to 0.80 W/m/K at 950ºC. Figure 4-3 (b)

shows the specific heat variation with temperature for gypsum plasterboard. The first

and second endothermic peak account for the first and second dehydrations that occur

at 100 to 150ºC and 150 to 200ºC, respectively (Keerthan and Mahendran, 2012a;

Thomas, 2010; Keerthan and Mahendran, 2012b). Figure 4-3 (c) shows the relative


density values that occur in gypsum plasterboards due to dehydration of the material

with a mass loss of 15%. The convective coefficient (h) were taken as 25 W/m2/K for

the exposed side and 10 W/m2/K for the unexposed side of the gypsum plasterboards

based on Keerthan and Mahendran (2012a). The surface emissivity of the gypsum

plasterboards was kept as 0.9 for all gypsum plasterboard surfaces.

(a) Thermal conductivity

(b) Specific heat at constant pressure

(c) Relative density

Figure 4-3: Thermal Properties of Gypsum Plasterboard (Keerthan and Mahendran, 2012a).

4.3.2 Insulation Material

LSF wall systems can be used with glass, rockwool or cellulose fibre insulation

material sandwiched between the plasterboard layers. Glass fibre is formed from

molten glass (silicate) fibres and is currently the most commonly used insulation in

Australia. Rockwool fibre is formed from basalt or iron ore blast furnace slag and

provides much higher levels of insulation and density.


Rockwool insulation was inserted within the cavities of the several of the wall systems.

The thermal properties of rockwool insulation utilised in this study was based on

previous research (Keerthan and Mahendran, 2012a; Thomas, 2010; Keerthan and

Mahendran, 2012b). Figure 4-4 shows the thermal conductivity of rockwool insulation

as a function of temperature. The specific heat of rockwool was kept constant at 840

J/kg/°C for temperatures up to 1200°C (Keerthan and Mahendran, 2012a).

Figure 4-4: Thermal Conductivity of Rockwool Insulation (Keerthan and Mahendran, 2012a).

4.3.3 Steel

The temperature increase of steel members is a function of its thermal conductivity

and the specific heat of steel. The precision in the determination of thermal properties

of steel, such as specific heat and thermal conductivity, has little influence on the

thermal modelling of LSF walls under fire conditions since steel framing plays a minor

role in the overall heat transfer mechanism of the LSF wall assembly. The Eurocode 3

Part 1.2 (CEN, 2005) thermal properties of steel were used in the developed FE

models. Figure 4-5 shows the specific heat of steel and the endothermic peak of 5000

J/kg/°C at 735°C.

Figure 4-5: Specific Heat of Steel in the Eurocode 3 Part 1.2 (CEN, 2005).

4.4 METHOD OF NUMERICAL STUDIES

4.4.1 General

This section details the modelling technique of the developed FE heat transfer models

of LSF walls system configurations. ABAQUS CAE was used as the finite element

software for thermal analysis (Simulia, 2014).


4.4.2 Thermal Boundary Conditions and Material Properties

The heat flux at the boundary will be calculated from the temperature of the fire curve

Tg and the temperature on the surface Ts according to Equation (4-1).

𝑞 = ℎ(𝑇𝑔 − 𝑇𝑠) + 𝜎𝜀(𝑇𝑔4 − 𝑇𝑠

4) (4-1)

where

q is the total heat flux, ε is the relative emissivity, σ is the Stefan–Boltzmann constant (5.67x10−8

W/m2/C4), Tg and Ts are the gas and surface temperatures, respectively. For fire exposure to the standard

cellulosic curve, Tg = 345log (8t+1) + 20. Convective heat transfer coefficient (h) is approximately 25

W/m2K on the fire exposed side, and it is 10 W/m2K on the unexposed side. Emissivity of 0.9 was used

for both exposed and unexposed surfaces.

The LSF wall components were modelled using heat transfer solid elements (DC3D8)

and then connected using tie constraints to ensure solid-solid heat transfer between

them. The top, bottom and sides of the walls were assumed to be insulated, thus no

heat transfer occurs through them.

There are three major heat transfer modes in FEA, namely; conduction, convection

and radiation. The conduction effect was defined using appropriate conductivity values

as discussed in Section 4.2. The convection heat transfer was defined by assigning

convective film coefficients of 25 and 10 W/m2/ºC on the fire and ambient sides,

respectively. These values were selected based on those proposed in the past research

studies (Keerthan and Mahendran, 2012a). Finally, the radiation heat transfer was

defined by assigning an emissivity value of 0.9 on all the LSF wall surfaces.

The standard fire curve was defined as an amplitude curve following a time-

temperature profile based on ISO 834, where θ = 345log (8t + 1) + 20, θ is the

temperature and (t) is the time. This was assigned to the fire exposed side as a boundary

condition. The temperature on the fire exposed side was assigned to follow the fire

curve, whereas room temperature was assigned to the ambient side of gypsum

plasterboards.

The Stefan-Boltzmann constant (σ) of 5.67x10-8 W/m2/ºC4 was also assigned to the

model. In addition to the boundary conditions, the models without cavity insulation

materials were modelled in ABAQUS CAE using closed cavity radiation in the

enclosures. The cavity surfaces enclosed by the LSF wall components were selected


first and then a cavity radiation emissivity of 0.9 was assigned to those surfaces. These

boundary conditions are shown in Figure 4-6.

Figure 4-6: Finite Element Modelling of LSF Wall Panel.

4.5 RESULTS

The results of the FE modelling are presented and discussed in this section.

Table 4-2 summarises the results of modelling the developed LSF wall systems.

Table 4-2: Comparison of FEA Predicted Fire Resistance Ratings of Conventional and

Innovative LSF Wall Systems.

Test

Specimen

No. Configuration

Time at

500°C

(min)

Time at

600°C

(min)

Increment

at 500°C

(%)

Increment

at 600°C

(%)

1

82 90 - -

2

99 113 21 26

3

98 112 20 24

4

113 125 38 39

5

124 136 51 51

Note: Stud is 90x40x15x1.15mm SCS and 58x40x10x1.15 SCS (for Test 4 and 5) fy = 500 MPa; Board

material = Gypsum Plasterboard; Insulation material = Rockwool Insulation; Back Blocking Board

length = 100mm.


Gunalan et al. (2013) determined the critical hot flange temperature of LSF wall

systems with 0.4 and 0.2 load ratios to be 500°C and 600°C respectively. Accordingly,

the comparisons of each configuration were completed by comparing the FE hot flange

time-temperature curves at 500°C and 600°C. Figure 4-7 (a) and (b) shows the FE hot

flange time-temperature profiles of the conventional and innovative LSF wall system

configurations at different critical temperatures.

(a) Hot - Flange comparison at critical temperature of 500°C (0.4 Load Ratio)

(b) Hot - Flange comparison at critical temperature of 600°C (0.2 Load Ratio)

Figure 4-7: Hot - Flange Time - Temperature Profiles of Conventional and Innovative

LSF Wall System Configurations at Different Critical Temperatures.


Configuration 1 obtained 82 min and 90 min at the critical hot flange temperature of

500°C and 600°C respectively. Figure 4-8 (a) and (b) show the temperature contours

across configuration 1 at different critical temperatures.

Configuration 2 achieved 99 min and 113 min at critical temperature of 500°C and

600°C respectively. Figure 4-9 (a) and (b) shows the temperature contours across

configuration 2 at different critical temperatures.

Configuration 3 obtained 98 min and 112 min at critical temperature of 500°C and



Configuration 4 achieved 113 min and 125 min at critical temperature of 500°C and



Configuration 5 obtained 124 min and 136 min at the critical hot flange temperature

of 500°C and 600°C respectively. Figure 4-12 (a) and (b) shows the temperature

contours across configuration 5 at different critical temperatures.

Comparing the obtained hot flange FE results for Configurations 2, 3, 4 and 5 against

Configuration 1 (conventional cavity insulated LSF wall system), the improvement of

the fire resistance ratings was 21%, 20%, 38% and 51% for a critical hot flange

temperature of 500°C respectively. For a critical hot flange temperature of 600°C the

improvement was 26%, 24%, 39% and 51% respectively.

(a) Temperature Contours across Configuration 1 at 82 min or 500°C


(b) Temperature Contours across Configuration 1 at 90 min or 600°C

Figure 4-8: Temperature Contours across Configuration 1 at Different Critical Temperatures.





4.6 CONCLUSION

This chapter has presented the details of the developed 3D finite element heat transfer

models of conventional and innovative LSF wall systems proposed for use in MBSs.

It has been considered in order to improve the fire performance of LSF wall systems

and to lessen the detrimental effect that cavity insulation has on the CFS studs.

Gunalan et al. (2013) described the critical hot flange temperature of LSF wall systems

with 0.4 and 0.2 load ratios to be 500°C and 600°C, respectively. Hence, comparisons

were made for each configuration by comparing the FE hot flange time-temperature

curves at 500°C and 600°C, respectively. The study showed that when the obtained

hot flange FE results for Configurations 2, 3, 4 and 5 were compared against

Configuration 1, the improvement of the fire resistance rating were 21%, 20%, 38%

and 51% for critical hot flange temperature of 500°C while they were 26%, 24%, 39%

and 51% for critical hot flange temperature of 600°C, respectively. Thus, this study

has shown the expected increase fire resistance performance of the newly proposed

wall systems. The selection of which configuration of LSF wall system to adopt within

a modular building system will be dependent on the fire rating requirement of the

structure.


Chapter 5: Conceptual Design of an

Improved Modular Building

System

5.1 INTRODUCTION

Modular construction offers an array of substantial benefits over traditional

construction methods. However, shortcomings in the development and practical

application of the technology has seen modular construction not fully attain these

ideals. Furthermore, the recent Grenfell Tower fire incident has criticised the safety of

steel frame structures and steel frame wall panel systems which are both often

employed in MBSs. This chapter proposes a conceptual design of an Improved

Modular Building System that addresses these concerns. This chapter begins with

discussing design considerations (Section 5.2) that re-examine and summarise the key

benefits and shortcomings derived from the case studies presented in Chapter 3. Next,

the design inputs that were taken into consideration for the design of the modular

building system are discussed (Section 5.3). Subsequent, the conceptual design of the

proposed modular building system is presented (Section 5.4) followed by the proposal

for multi-storey configurations (Section 5.5). Finally, a summary of the design is

presented and concluding remarks are made (Section 5.6).

5.2 DESIGN CONSIDERATIONS

Through the examination of several case studies of recent modular building designs

(Chapter 3), a concise summary of shortcomings and benefits is summarised as

follows. These shortcomings and benefits have contributed to developing this

improved modular building system.

5.2.1 On site Construction Efforts

From Chapter 3, several MBS projects required a fair degree of labouring on-site

resulting in longer construction times, increased safety concerns and greater financial

burden. The curing of concrete for the construction of SOHO Apartments engineered

by Irwinconsult resulted in lengthy construction times. The lengthy construction time

is due to waiting for the concrete to cure and amass the required strength before safe

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construction of the upper levels could continue. However, Irwinconsult were able to

mitigate this issue by designing the steel chassis of the modules to withstand the load

of four modules. This allowed for construction and placement of the modules to run

simultaneously whilst preparing, pouring and curing of the concrete elements took

place.

5.2.2 Alignment Issues

Alignment issues were prevalent in several of the reviewed MBSs. Theoretically, it is

possible to design a construction process that sees minimal tolerance. Though, a real-

world environment exists, and unforeseen events and/or circumstances can occur that

can easily change a module and its properties. When addressing alignment issues, the

designer should develop several measures for adjustability when assembling the

modules together on site. The Verbus System addressed alignment issues by

developing a suitable connection, the corner casting connection. The lugs seen in the

corner castings have been shaped to guide themselves into the openings of the corner

castings and then are bolted in place.

5.2.3 Effectiveness of Connections

Several connections were impractical for on-site construction. Some were difficult to

install effectively and safely whilst there were others that were time consuming. When

designing the connections, the designer should develop connections that are simple,

structurally effective and practical in terms of on-site module-to-module assembly.

The compatibility of the connections with existing technologies including the

technologies to connect, disconnect, assemble, relocate and fix (tie down) should be

well considered. Vector Praxis and Verbus Systems designed connections based on

ISO corner castings seen in standard freight containers. The compatibility of their new

connections with existing technologies allowed their modular systems to be easily

assembled and transport with little to nil modifications of current technologies.

5.2.4 Weight of Modular Building Systems

The MBSs with the height accomplishing feats were also the heaviest systems

reviewed. The need for stronger building materials often results in heavier, denser-

grade materials. This dilemma cannot be avoided; however, it can be minimized

through the application of greater strength-to-weight ratio building materials.


The large hot-rolled sections in Arup’s 421 Dean structure and Irwinconsult’s SOHO

Apartments structure resulted in heavier module designs. Paradoxically, the heavier

gauge members also provided additional strength allowing both parties to construct a

tower to such heights.

The thinner CFS sections prevalent in Octavio’s and Pascual’s system and the Verbus

System resulted in modules that were light-weight and structurally sufficient to

withstand the loading of several stories. However, these systems were structurally

limited to several stories and the heights seen in Arup’s and Irwinconsult’s systems

cannot be reached without adjustment to the designs. Thus, it is here where the

introduction of strengthened CFS sections are prescribed such as the Rivet-Fastened

RHFCB.

5.3 DESIGN INPUTS

Designing a modular system encompasses a range of fields and aspects that the

designer must consider for the modular system to function effectively and maximise

the benefits that modular construction offers. The following sections describe several

aspects of the system’s design that have been taken into consideration. The Handbook

for the Design of Modular Structures by Monash University (2017) has been referred

to in developing the following section.

5.3.1 Overall Tower Stability

The overall stability and robustness of a modular tower structure is governed by the

loading interactions and tying actions that individual modules have on their

neighbouring modules. Overall stability can be provided by an external structure or by

individual modules acting together in unison. To maximise the benefits of modular

construction (quick construction, low costs) the designer should opt to address the

overall stability of a structure through the interactions and tying actions of the

individual modules.

The proposed modular system design suggests that the overall stability of the structure

is to be attained through the collective interactions of the modules via several proposed

bracing systems. The wall systems of the modules provide the bracing capacities of

the individual modules and through appropriate connection methods between modules

these forces can be dispersed across the entire structure.

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5.3.2 Acoustic Performance

The acoustic properties of a structure are a significant aspect to consider when

addressing the comfort of the occupants. Sound is the term use to describe the

vibrations that travels through any medium. Sound is quantified through frequency and

amplitude. There are two types of sound classification; airborne sound and impact

sound. Airborne sound describes the sound that is transmitted through the air such as

speech or music. Impact sound describes the sound caused by impact and transmitted

through the structure such as footsteps or dropped objects.

The acoustic performance of a structure is regulated by the sound insulation present in

the structure. Sound plays a significant role in the overall sustainability structure and

thus, designers must consider the impacts that the acoustic performance has on the

sustainability of a structure. Acoustic performance can be controlled through adopting

several measures such as:

• Employing materials with poor stiffness properties;

• Incorporating damping materials in the structure;

• Increasing the depth of the wall cavities; and,

• Increasing the mass (especially thicknesses) of the incorporated materials.

The proposed modular system design has regulated the acoustic performance of the

system by incorporating a double ceiling and double wall partition configuration (2x

layers of gypsum plasterboard). The double layer provides a thicker depth of material

and a break in continuity of the material that sound must traverse through. Gypsum

plasterboard was chosen as it performs highly in reducing the transmission of sound

energy as well as being a high fire-resistant material. In addition to the gypsum

plasterboards, rockwool is housed within the cavities of the system as an insulating

material. This helps to further regulate acoustic transfer.

5.3.3 Thermal Performance

The thermal performance of a structure can be described as the capacity to regulate

and control the temperatures exposed to the structure. Thermal regulation is essential

in ensuring the comfort of the occupants and the protection of the structure from

exposure to unreasonable temperatures. Thermal performance is quantified by the heat

loss per m2 of the façade or roof (U-value). Selection of thermal regulation measures


is integral to contributing to the sustainability of a structure. Thermal regulation can

be provided by several means such as:

• Thermal insulation products (insulation batts);

• Heating and cooling appliances (air conditioners and heaters);

• Preventing air infiltration and leakage by sealing gaps; and,

• Ventilation and control of condensation.

The thermal regulation measures adopted in the proposed modular system design is

provide through introducing rockwool (an insulative material) into the cavities of the

wall, roof and floor systems. Rockwool was chosen as the insulating material based on

the multiple benefits that it provides over other insulating materials including:

• Great thermal insulating properties;

• Advanced acoustic insulating properties;

• Breathable structure; and,

• Capacity to withstand exposure to high temperatures before melting

(+1000℃).

5.3.4 Fire Resistance

The fire performance of buildings and structures is an essential element of the design

process. The designer must consider the possibility and effects that a fire would have

on the structure including the risk of spread to other parts of the structure and even

neighbouring structures. The designer should incorporate measures to prevent the

spread of a fire and measures to delay the onset of structural failure and collapse caused

by exposure to a fire.

The fire performance of a structure is governed by selection of materials, the

arrangement and profile of structural members and any firefighting systems in place.

In Australia the National Construction Code dictates the requirements for the fire

resistance of a structure.

In this proposed design several measures have been incorporated to ensure the system

best meets the fire performance requirements. The fire resistance measures proposed

include:

• Incorporating Rockwool in the cavities of the system;

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• Proposing a discontinuous arrangement for the insulating materials;

• Employing double layer Gypsum Plasterboard arrangements; and,

• Integrating back blocking boards on the flanges of the internal frame

members (such as steel wall stud).

Contradictory of its intended purposes, employing insulation to completely fill the

cavities of a wall system has been previously shown to have a negative effect on the

fire resistance performance of the wall system. Adopting a discontinuous cavity

arrangement for the insulation material can simulate a uniform temperature

distribution on the steel members of the wall frame.

Gypsum plasterboard is chosen for its advanced fire resistance properties.

Incorporating a double layer configuration lengthens the heat transfer path to the

critical steel frame members and hence, increases the fire resistance performance.

Addition of another layer of gypsum plasterboard further increases the heat transfer

path and fire resistance performance but also introduces unnecessary and inefficient

use of materials. By limiting the width of the board to the width of the flange of the

steel frame member a back-blocking board is formed. The back-blocking board

reduces the quantity of material used and thus, saving costs and minimizing weight

while providing improved fire resistance performance.

5.3.5 Sustainability

With recent emphasis on developing sustainable structures, designers must consider

the entire lifecycle of a structure. Modular systems provide a great foundation for

sustainable practices as the systems inherently provide measures to systematically

disassemble the structure and salvage the constituent parts avoiding the need for

destructive demolition. Modular systems are also capable of being reused as an entire

system by dismantling and relocating the modules elsewhere. With these factors in

mind, the designer should consider the processes for dismantling the modular as

constituent parts and/or as entire modules for relocation.

The proposed modular system design utilizes simple connections that are reversible

and thus keeps the dismantling process easy. By using bolted connections, the system

can be easily undone using appropriate tools. The clutching hold of the wall studs by

the wall track is easily dismantled. The rivet connections of the Rivet-Fastened

RHFCBs can be removed allowing the flanges and web of the section to be recycled.


5.4 PROPOSED MODULAR BUILDING SYSTEM CONCEPTUAL

DESIGN

The modular building system conceptual design is proposed in this section. This

conceptual design encompasses a complete MBS module suitable for single storey

applications; multi-storey configurations are later discussed in Chapter 5.5 (i.e. top and

intermediate modules is discussed). The floor, roof and wall systems that form the

module are presented as well as the connections within the module. Note, the nominal

sizes presented in this section are general sizes for illustrative purposes. Specific sizes

have not been stated as they would vary with application, load and other project

specific requirements.

5.4.1 Module Structural Scheme Overview

The proposed design takes the form of a corner supported modular system with a wall

system that contributes to the cross bracing strength of the modules. Figure 5-1

presents an overview rendering of the proposed modular system.

Figure 5-1: Overview of the proposed modular system.

The system is designed to provide fully open sides by transfer of loads through the

longitudinal edge beams (Rivet-Fastened RHFCB) to the corner posts (SHS). This

allows designers to take advantage of the wider open spaces that the fully open-sided

modules provide. It is intended that the proposed modules will be be placed side by

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side to create larger open plan spaces, as required in hospitals, schools, open settings

and alike. The internal skeleton arrangement of the proposed modular building system

is presented in Figure 5-2.

Figure 5-2: Isometric view of the internal skeleton arrangement of the modular system.

The corner posts provide the compression resistance and are typically 100 x 100 x 10

SHS members. The Rivet-Fastened RHFCB is employed as the edge beams which are

connected to the corner posts by fin plates that provide nominal bending resistance.

Shallower Rivet-Fastened RHFCB are employed as the joist members in the roof and

floor systems. The Rivet-Fastened RHFCB is employed widely throughout this system

and further discussion for this design selection is presented in Section 5.4.2.

The roof and floor system configurations are presented in Sections 5.4.4 and 5.4.5,

respectively. Their optimum designs are developed based on studies conducted by

Baleshan and Mahendran (2017).

Several wall system configurations are presented in Section 5.4.6. Selection of the final

wall system is dependent on the requirements of each specific module’s given location,

placement and loading conditions.

This conceptual design also presents several bracing systems. Details of these bracing

systems are presented in Section 5.5.


5.4.2 Application of the Rivet-Fastened RHFCB

The Rivet-Fastened RHFCB is used extensively throughout the system. The Rivet-

Fastened RHFCBs are not only cost effective, but also of comparable strength as

flexural members as Siahaan et al. (2017) found. Rivet-Fastened RHFCBs are on

average 40 to 50% lighter than traditional hot rolled structural steel beams of

equivalent structural performance. It is an ideal hollow flange flexural member that

can be used as the floor joist and bearer in LSF ceiling, floor and wall arrangements of

MBSs due to its significantly lighter weight. In addition, the Rivet-Fastened RHFCB

possesses a flexible design that allows the designer to select various combinations of

web and flange widths and thicknesses to suit the required applications.

Siahaan et al. (2017) recommended 100mm rivet spacing for Rivet-Fastened RHFCBs

based on their section moment capacity studies. They found a reduction of 10-15%

when using 100mm rivet spacing. The mono-symmetric section of the Rivet-Fastened

RHFCB is preferred by the industry as it can provide a greater number of connection

types. Rivet-Fastened RHFCBs can also be lifted and carried like structural timber

beam sections. Rivet-Fastened RHFCB can be cut, nailed, screwed and drilled on site

where necessary.

In various applications, connectivity between fire protective composite panels are

significantly improved when using Rivet-Fastened RHFCB instead of conventional

open CFS sections. This is due to the screws penetrating through both inner and outer

flanges of Rivet-Fastened RHFCBs. This stronger connection is expected to improve

the lateral stability of LSF floor systems and delay the fall-off time of plasterboards

under fire conditions consequently improving the fire rating of LSF floor systems.

Rivet-Fastened RHFCBs deliver a higher and more efficient structural performance in

terms of load bearing capacity, bending moment capacity and deflection from the

available steel. It is for this reason that they are incorporated into the following

proposed design.

5.4.3 Module Chassis

The module’s chassis bears the grunt of the loading. The proposed framework/chassis

of the module is formed from CFS members that include: Square Hollow Section

(SHS) columns and Rivet-Fastened RHFCBs edge beams that are bolted together

through welded fin plate connections stemming from the corner posts. The

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arrangement of the module chassis members is shown in Figure 5-3. Details of the

structural components of the module chassis are presented in Table 5-1.

Figure 5-3: Isometric view of the arrangement of module chassis members.

Table 5-1: Details of the internal skeleton members of the module.

Module Chassis Structural

Component

Section Profile

Corner Post SHS 100x100x10

Edge Beam (Floor) Rivet-Fastened RHFCB 250x75x25x3x3

Edge Beam (Roof) Rivet-Fastened RHFCB 200x75x25x3x3

Connection 1 Connection B – Welded Fin Plate

5.4.4 Roof System

The roof system employs the Rivet-Fastened RHFCB in two applications; they are

employed as the joists and edge beam members. The roof joists are connected to the

larger roof edge beams via a single angle cleat connection (Connection A, see Section

5.4.7). The connection consists of an angle-shaped flat plate with a total of four bolt

holes to attach to the members (two bolts for each member).

On the top and bottom flanges of the edge beam, an inner and outer shell exists in the

form of a thin steel sheet (0.55mm). Attached to the inner shell are two layers of

gypsum plasterboard (16mm each) connected via roof screws and providing advanced

fire protective measures. Sitting on top of the outer shell is a layer of plywood (16 mm)

connected via roof screws as well.


A section view of the roof system is presented in Figure 5-4. Internal section views of

the roof system are presented in Figure 5-5 and Figure 5-6. The side view of the roof

system is presented in Figure 5-7 . Details of the roof system profile is presented in

Table 5-2.

Figure 5-4: Section view of the roof system.

Figure 5-5: Internal section view of the roof system from the outside the module.

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Figure 5-6: Internal section view of the roof system from the inside of the module.

Figure 5-7: Side view of the roof system.

Table 5-2: Details of the roof system profile.


Edge Beam Rivet-Fastened RHFCB

200x75x25x3x3

Roof Joist Rivet-Fastened RHFCB

150x60x20x2x2

Internal Shell Steel sheet 0.55mm

Internal Roof Lining (Ceiling) 2x Layers of Gypsum Plasterboard 16mm (each)

External Shell Steel Sheet 0.55mm

External Roof Lining Plywood 16mm

Connection 1 Connection A – Single Angle Cleat


Connection 3 Roof Screws


5.4.5 Floor System

Edge beams in the form of Rivet-Fastened RHFCB encircle the floor system. These

beams are connected to the corner posts via a welded fin plate connection (Connection

B, see Section 5.4.7). The edge beams act as the main floor load bearing members and

effectively transfer their loads to the corner posts.

Within the extents of the floor’s edge beams, floor joists are slotted in between and

provide the capacity to support the floor. These floor joists are smaller Rivet-Fastened

RHFCBs that are connected to the larger edge beams via a single angle cleat

connection (Connection A, see Section 5.4.7).

Upon the edge beams, a steel sheet underlies the plywood flooring as depicted in

Figure 5-11. The plywood flooring is connected to the floor joists by using nails.

Beneath the floor joists a second steel sheet followed by two layers of gypsum

plasterboards complete the floor system. The steel sheet and gypsum plasterboards are

connected to the floor joists using nails. Gypsum plasterboard is chosen as it provides

substantial fire performance ratings.

A section view of the floor system is presented in Figure 5-8. Internal section views of

the floor system are presented in Figure 5-9 and Figure 5-10. A side view of the floor

system is presented in Figure 5-11. Details of the floor system profile is presented in

Table 5-3.

Figure 5-8: Section viewof the floor system.

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Figure 5-9: Internal section view of the floor system from the outisde of the module.

Figure 5-10: Internal section view of the floor system from the inside of the module.

Figure 5-11: Side view of the floor system.


Table 5-3: Details of the floor system profile.


Edge Beam Rivet-Fastened RHFCB

250x75x25x3x3

Floor Joist Rivet-Fastened RHFCB

200x60x20x2x2

Internal Shell Steel sheet 0.55mm

Internal Floor Lining (Flooring) Plywood 16mm

External Shell Steel Sheet 0.55mm

External Floor Lining 2x Layers of Gypsum Plasterboard 16mm (each)

Connection 1 Connection A – Single Angle Cleat


Connection 3 Floor Screws

5.4.6 Wall System

Several wall system designs are presented in this section. As this is only a conceptual

design, these wall systems have been selected to highlight the many benefits they have

over a standard wall system. It is recommended that these wall systems be further

studied to determine their complete behaviour characteristics.

Wall System 1: Stiffened Channel Section Double Board Wall System

Wall System 1 is the stiffened channel section double board wall system. This system

is based on the standard LSF wall system with the addition of innovative measures

including the stiffened channel section for the wall studs and a double layer of gypsum

plasterboard on each side of the frame. Dias et al. (2017) showed that the stiffened

channel section is as structurally efficient as the LSB but also a more economical

alternative due to eliminating the need for welding and thereby reducing fabrication

costs. In addition, Dias et al. (2017) also showed that the stiffened channel section is

equivalent to the LSB in terms of fire resistance performance.

Wall System 1 is a simple wall frame bounded by an internal and external shell as well

as lining. A top and bottom wall track with the profile of a standard channel section

holds together the wall studs with the profile of stiffened channel sections. Enclosing

this assembly are two layers of gypsum plasterboard on each side (internal and

external) of the wall frame.

Screw connections are used to fix the floor wall track to the wall studs, and to fix the

roof wall track with the wall studs. The screw connections are a simple and effective

connection that is also easy to assemble and disassemble. In addition, the screw

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connections allow the wall studs to expand from thermal expansion without unduly

stress. Details of the conventional wall system frame is presented in Table 5-4. An

isometric and section view of the Wall System 1 is presented in Figure 5-12 and Figure

5-13 respectively.

Table 5-4: Details of Wall System 1.


Wall Stud Stiffened Channel Section

Wall Track (Top) CFS Channel Section

Wall Track (Bottom) CFS Channel Section

Wall Lining (Internal) 2x Layers of Gypsum Plasterboard 16mm (each)

Wall Lining (External) 2x Layers of Gypsum Plasterboard 16mm (each)

Connection Wall Screws

Figure 5-12: Isometric view of the conventional wall system frame.

Figure 5-13: Section view of the conventional wall system connected to the module chasiss.


Wall System 2: Wall System with Discontinuous Cavity Insulation

Wall System 2 (initially presented in Chapter 4) employs a discontinuous cavity

insulation arrangement. Stiffened Channel Sections form the wall stud members and

standard Channel Sections form the wall track member. A double layer of gypsum

plasterboard is attached to each side of the frame via screw connections. Rockwool

(acting as the insulation material) is inserted in the internal cavities of the system in a

discontinuous configuration with voids left adjacent to both sides of the wall studs.

These voids aid to simulate uniform temperature distribution on the steel wall studs

that improve fire performance as discussed in Chapter 4.

Details of Wall System 2 are presented in Table 5-5, and overview, detailed view and

section view presented in Figure 5-14, Figure 5-15, Figure 5-16 respectively.




Wall Track (Bottom) Channel Section

Wall Track (Top) Channel Section

Internal Wall Lining 2x Layers of Gypsum Plasterboard 16mm (each)

External Wall Lining 2x Layers of Gypsum Plasterboard 16mm (each)

Insulation Rockwool


Figure 5-14: Overview of Wall System 2.

Figure 5-15: Detailed view of Wall System2.

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Figure 5-16: Section view of Wall System 2.

Wall System 3: Wall System with Discontinuous Cavity Insulation and Back-

Blocking Board

Wall System 3 (initially presented in Chapter 4) adopts a similar arrangement to Wall

System 2. Stiffened Channel Sections are used as the wall studs and standard Channel

Sections as the wall track members. Wall System 3 also adopts a discontinuous cavity

arrangement with rockwool similar to Wall System 2. The difference between the

systems is the implementation of a back-blocking board in Wall System 3. The back-

blocking board is attached to the flange of the Stiffened Channel Sections (wall studs)

succeeded by the double layer of Gypsum Plasterboard. All three layers of plasterboard

are attached to each flange (top and bottom) of the wall studs using screw connections.

Details of the components found in Wall System 3 are presented in Table 5-6. A

overview, detailed view and section view of Wall System 3 is presented in Figure 5-19,

Figure 5-17 and Figure 5-18 respectively.





Internal Wall Lining 2x Layers of Gypsum Plasterboard 16mm (each)

External Wall Lining 2x Layers of Gypsum Plasterboard 16mm (each)

Back Blocking Board Gypsum Plasterboard 16mm

Insulation Rockwool





Figure 5-18: Detailed view of Wall System 3.


Wall System 4: Walls with Double Skin Steel Panels

Wall System 4 is an adaption of the Double Skin Steel Panel Wall System initially

presented in Chapter 3. Hong et al. (2011) showed that the lateral load capacity of a

bare frame module can be increased by up to four folds by implementing their panel

configuration. Their panel configuration has been built upon and improved here.

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Wall System 4 consists of Stiffened Channel Sections as the wall studs effectively

replacing the corrugated steel sheet seen in the works of Hong et al. (2011). The

stiffened channel sections are bordered by thin steel sheets that are connected via

screws. By employing screw connections over soldered connections, the assembly

times of these steel panels are expected to shorten. These panels are slotted between

wall tracks that have been implemented into the chassis.

The steel panels are arranged in intermediate spacing intervals as shown in Figure

5-22. An overview and section view of Wall System 4 is presented in Figure 5-20 and

Figure 5-21 respectively. Details of the components found in Wall System 4 are

presented in Table 5-6.






Internal Wall Lining Steel Sheet

External Wall Lining Steel Sheet





Figure 5-22: Isometric view of the double skin steel panels within the frame of a module.

5.4.7 Connections

Connections are critical in the design of modular structures as they determine the load

paths that distribute the forces applied to the structure. The designer must consider

several aspects specific to MBSs when developing the connections of a modular

system. These are:

• Robustness of the structure, specifically discontinuities and load paths;

• Ease of assembly on site and in the manufacturing facility; and,

• Disassembly potential for reuse, recycle and sustainability opportunities.

The following sections present the connections chosen for employment in the proposed

modular building system. Note, Module-to-module connections are omitted from this

study as the interaction behaviour between modules become complex when modules

are arranged together to form a building.

Connection A: Single Angle Cleat Connection

Connection A is a single angle cleat that attaches the joists to the edge beams together

via two bolts. This simple connection has bolt holes that have been modified to

mitigate tolerance issues. Connection A is seen in Figure 5-23 and Figure 5-24.

Joist to Edge Beam Interface

The joists carry the loading from its application (floor or roof) and transfers them to

their respective edge beams. The Rivet-Fastened RHFCB is of advantage in this

168

application as it allows the floor and roof greater bearing capacity, bending moment

and deflection. It also provides a light-weight options which results in higher structural

efficiency. The joists are connected to the edge beams via a single angle cleat. The

floor joists to floor edge beam interface is presented in Figure 5-23, and the roof joists

to roof edge beam interface is presented in Figure 5-24.

Figure 5-23: Floor joists to floor edge beam interface.

Figure 5-24: Roof joists to roof edge beam interface.

Connection B: Welded Fin Plate Connection

Connection B is a welded fin plate connection that is assembled in the factory during

the assembly of the modules. The welded fin plate is welded to the corner posts and

connected to the edge beams via either two (roof) or three (floor) bolts. The bolt holes

have been modified to mitigate tolerance issues. The edge beams transfer their loads

to the corner posts which transfer the loads to the ground. Connection B is seen in

Figure 5-25 and Figure 5-26.

Edge Beam to Corner Post Interface

The edge beams transfer the loads on its application (floor or roof) to the corner posts

that effectively transfer these loads to the ground. The edge beams are attached to the


corner posts using a welded fin plate connection (Connection B). The welded fin plate

is welded to the corner posts and the edge beam is attached to the fin plate via two

bolts. The roof edge bam to corner post interface is seen in Figure 5-25.

Figure 5-25: Isometric view of the roof edge beam to corner post interface.

Figure 5-26: Isometric view of the floor edge beam to corner post interface.

Connection C: Screw Connection 1

Connection C (seen in Figure 5-27) is a simple screw connection seen in the connection

of the floor and roof level wall tracks to wall studs. Incorporating a secured screw

connection to the top and bottom of the wall studs fixes the members in place. The

screw penetrates through the flanges of the wall track and into the flange of the wall

stud. The simplicity of the screw connection allows the members to easily be

disassembled and reused improving the sustainability of the proposed modular

structure.

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Figure 5-27 Isometric view of the wall system illustrating Connection C.

Connection D: Screw Connection 2

Connection D (seen in Figure 5-28) is also a simple screw connection, though it is seen

where linings (steel sheet, plywood and/or gypsum plasterboard) are attached to the

rivet-fastened RHFCB. This connection deviates from the Connection C: Screw

Connection 1, by which the screws penetrate both the inner and outer flanges of the

Rivet-Fastened RHFCB. In doing so, it is expected that the connectivity and lateral

stability of the roof, floor and roof sections are improved.

Figure 5-28: Side view of the Floor System illustrating Connection D.

5.5 MULTI-STOREY CONFIGURATIONS

Without an external lateral load resisting system, the proposed module presented

earlier in this chapter is only suitable for application in multi-storey structures up to

three stories. Inevitably, due to lateral loading conditions a dedicated lateral loading

system must be adopted to achieve greater heights. This section presents the system


configurations proposed for when constructing structures greater than three stories.

Note, only brief discussions about the proposed multi-storey configurations are

presented with further investigation of these systems recommended.

It is proposed that an integrated lateral load resisting system is adopted. The integrated

system is comprised of the combined actions of the individual module bracing systems

working together with a central/overall tower bracing system and the individual

actions of the module-to-modulae connections. The central tower bracing system may

be in the form of a concrete or steel core or exoskeleton bracing system. The combined

actions of the individual modual bracing systems have the potential to minimize the

effective lateral loading on the central tower bracing system. The following sections

briefly discuss two concepts for individual module bracing systems. Further

investigation should be undertaken to fully undertand the combined actions of

individual modules in a multi-storey arrangement; doing so will allow designers to

develop modular costructed buildings of great heights.

5.5.1 Intermediate Level Module Configuration

The type of module configuration presented in Chapter 5.4 is the module configuration

for single storey applications. For multi-storey applications, a slightly different module

configuration is introduced and placed beneath the single storey module to form the

multiple storeys of the building. This module is called an intermediate module and the

single storey module can be referred to as the roof module. The intermediate modules

are subjected to a slightly different set of loading that the roof module is subjected to

and thus will slightly differ in configuration.

The intermediate modules will no longer comprise of a roof system but instead of a

top-level system. By convention, the floor systems should also be called bottom-level

systems. The top-level systems of the intermediate modules adopt the same

configurations of the roof systems seen in the roof module with the exception of the

edge beam and joists sizes. The size of the edge beam and joists of the top-level system

are now identical to their bottom-level counterparts.

5.5.2 Module Cross-Bracing System

Cross-bracing systems are a well-developed lateral load resisting technology with

application seen abundantly in the building industry. The cross-bracing system in this

proposed design is composed of thin flat steel strips arranged in a X (cross) setting

172

(see Figure 5-29) that act only in tension. The steel strips are connected to the external

faces of the corner posts, edge beams and wall studs (at intermediate intervals) of the

modules. As the steel strips are thin, they do not interfere with the assembly of the

outer linings of the module. The long walls comprise of a pair of cross bracing systems

and the end walls comprise of a single cross bracing system. M. Lawson, Ogden, and

Bergin (2012) recommends that a modular structure of 4-6 stories can be achieved

when utilising cross-bracing systems and without a central tower bracing system. For

high loading, the width and grade of the steel strips can be increased.

Figure 5-29: Cross bracing multi-storey configuration (left – side view, middle – front view,

right – isometric view).

5.5.3 Double Skin Steel Panel System

The effectiveness of employing the double skin steel panel system for multi-storey

configurations was originally introduced in Chapter 3. A hypothesised improved

alternative to the original design was presented in Section 5.4.6 as Wall System 4. The

panel system comprises of wall studs in the form of stiffened channel sections bordered

by an internal and external layer of thin steel sheeting. The panels are inserted at

intermediate spacing intervals in the bare frame of a steel module. For the long walls


a pair of the panel systems is inserted and for the end walls a single panel system is

inserted. The arrangement of double skin steel panels is presented in Figure 5-30.

Figure 5-30: Double skin steel panel multi-storey configuration (left – side view, middle – front

view, right – isometric view).

5.5.4 Module-to-Module Connections

Module-to-module connections have been omitted from this study. Their behaviour

becomes complex as they must account for the interactions of module-to-modules and

the elements within the modules.

5.6 CONCLUSION

This section has presented the conceptual design of the proposed modular building

system. The complete framework of a module is presented and further dissected into

individual systems for discussion as the: chassis, floor system, roof system, wall

system and connections. Several designs of the wall system are presented. The

proposed design is suited to single storey configurations with multi-storey

configurations briefly discussed. Finalisation of the conceptual design would require

further analysis of the structural loading requirements.

174

Chapter 6: Conclusions

6.1 CONCLUSIONS

The modular construction method and modular building systems are construction

technologies capable of delivering results superior to traditional construction means.

The potential benefits of this technology over traditional means include time, costs and

waste savings. These benefits are made possible by the streamlined, systematic and

assembly line-like production of the modules used to form the buildings. In addition,

modular construction allows multiple construction phases to be completed

simultaneously and not be dependent on each other. These capabilities are yet to be

fully realised due to several shortcomings and drawbacks in the technology’s infant

development. Examination of real-life projects and case studies have revealed the

shortcomings to be: poor structural efficiency (strength-to-weight ratio) of the MBS

designs, lack of construction tolerance control, impractical to construct designs, and

lack of fire resisting measures. This thesis sought to address these shortcomings by

conducting series of studies to further the understanding of modular construction and

proposing solutions to the shortcomings. A brief summary of these studies are

presented below; further details of these works follow in later sub-sections.

A literature review was performed to establish the background and current

understanding of MBSs. Cold-formed steel and the Rivet-fastened Rectangular

Hollow Flange Channel Beam was also reviewed as it is later introduced as an

innovative solution to addressing the shortcomings of MBSs. It was found that the

Rivet-fastened RHFCB is superior in structural efficiency compared to conventional

CFS sections and other CFS sections. In addition, the section also considered easier to

produced, and thus lower in costs.

Case studies on recent modular construction projects were completed to pinpoint the

drawbacks and shortcomings of this technology and to establish the current advances

in the field. Case studies were also performed on current developing modular

technologies that seek to address the shortcomings. It was found that construction

tolerance is a major issue in some of the case studies. Most of the case studies also

lacked structurally efficient designs.


Several wall systems are developed and introduced as improved module components

that address the shortcomings of structural efficiency and fire-resisting performance.

These wall systems undergo thermal modelling to best understand their behaviour

under elevated temperatures. It was found that introduction of discontinuous cavity

insulation and backing boards contributed to improve the fire resistance rating by up

to 51%.

The innovative concepts presented throughout this study were then conglomerated and

used to develop an improved MBS module suitable for single-storey applications only.

Details of the structural components of the proposed design are presented. Finally, the

application of the module in multi-storey configurations is explored.

The study concludes with further recommendations for the proposed concepts to be

investigated before application into the real world. It is also recommended that

statutory standards specification document be developed immediately for the design

of MBSs.

6.2 LITERATURE REVIEW

This study presented a thorough literature review (Chapter 2) of cold-formed steel and

modular building systems. The following findings from the examination of cold-

formed steel are noted:

• CFS has many benefits over its HRS counterpart such as higher efficiency

in terms of strength-to-weight ratio and easier to manufacture and produce.

• Experimental studies of the Rivet-Fastened RHFCB show that the section is

structurally superior to conventional sections in respects to flexural, shear

and web crippling behaviour.

• A lack of specifications exist that appropriately address the design of

structures using the Rivet-Fastened RHFCB.

• The Rivet-Fastened RHFCB offers many benefits for utilisation in MBSs.

A thorough examination of MBSs was presented. The following findings are noted:

• The development of modular construction is still at its early stages and there

is yet to exist a statutory standards specification document for the design of

modular building systems.

176

• MBS modules can be categorised by their structural frame form. These

categories are:

o Four-sided modules;

o Partially open-sided modules;

o Corner-supported modules; and,

o Open-ended modules.

6.3 CASE STUDIES

Case studies of current industry developments including complete MBSs, wall systems

and connections specific to MBSs were presented in Chapter 3. The current advances

presently being implemented and/or studied in the modular construction field include:

• Arup’s complex steel bracing skeleton design of 461 Dean made the world

record breaking tallest modular constructed building possible.

• Irwinconsult’s hybrid use of concrete and steel materials in SOHO

Apartments to develop Australia’s tallest modular constructed building.

• Octavio and Pascual’s conceptual design kept the structural arrangement of

their MBS simple and economical for the building’s intended purpose as

student accommodation residences.

• CIMC’s patented Verbus System incorporated corner castings as

connections that had been designed based on the same corner castings seen

in ISO freight containers. This inclusion in their system maximised the

compatibility of their systems with current conventional transportation,

hoisting and lifting equipment.

The case studies were also able to pinpoint and define specific shortcomings of MBSs

in real world practice. The shortcomings include:

• 461 Dean’s design failed to appropriately address tolerance and positioning

concerns which led to extended project delivery delays.

• Although Irwinconsult developed effective techniques to minimize project

delivery time, the use of insitu concrete elements still demands a lengthy

curing time.


• Octavio and Pascual’s design incorporated welded connections which are

expensive and time costly to incorporate.

• Installation of CIMC’s Verbus System corner castings requires external

access when installing the modules on site which introduces a safety concern

for the installers.

6.4 THERMAL MODELLING OF LIGHT GAUGE STEEL FRAMED

WALL SYSTEMS PROPOSED FOR MODULAR BUILDING SYSTEMS

Chapter 4 presented a set of innovative LSF wall systems that had been developed with

advanced fire rating performances and with specific application to the later proposed

modular building system. The wall systems consisted of light-gauge steel frames

compounded by gypsum plasterboard layers in several compositions and with cavity

insulation in various arrangements. The LSF wall systems were built upon current

advances and their performance were analysed using 3D heat transfer finite element

modelling using ABAQUS.

To appropriately conduct the finite element modelling of innovative LSF walls

systems, the thermal properties of the materials in the wall systems were defined and

the method of analysis was established. The results of the analysis showed:

• Cavity insulation has a detrimental effect on the fire resistance performance

of the wall systems for a given arrangement due to the significantly lower

thermal conductivity of the insulation material.

• To improve this and to lessen the detrimental effect that cavity insulation

has on the CFS studs, innovative wall configurations were proposed using

discontinuous cavity insulation and 100 mm gypsum back-blocking boards.

• Gunalan et al. (2013) described the critical hot flange temperature of LSF

wall systems with 0.4 and 0.2 load ratios to be 500°C and 600°C,

respectively.

• Thus, hot flange FE results for Configurations 2, 3, 4 and 5 were compared

against Configuration 1 at critical hot flange temperatures. Improvement of

the fire resistance rating were 21%, 20%, 38% and 51% for critical hot

flange temperature of 500°C while they were 26%, 24%, 39% and 51% for

critical hot flange temperature of 600°C, respectively.

178

6.5 PROPOSED CONCEPTUAL DESIGN

Chapter 5 brought together the shortcomings of MBSs and relevant current

engineering advances to propose an improved and innovative modular building

system. The concept proposed is for single storey applications. The following design

details are noted:

• The proposed concept adopted a corner-supported module chassis where:

o horizontal loads are concentrated through the edge beams; and,

o vertical loads are concentrated through the columns.

• Light-weight and structurally efficient rivet-fastened RHFCBs formed the

edge beams of the module chassis while SHS formed the corner posts.

• Floor and roof system concepts were proposed employing the rivet-fastened

RHFCB as the joist members.

• Several wall system configurations were proposed for incorporation into the

conceptual module design.

• The wall systems act as the main lateral bracing elements.

• Simple connections were adopted throughout the module where the basis of

selection was to minimize the efforts and costs of assembly.

• The Rivet-Fastened RHFCB was used widely throughout the system for its

structurally efficient (weight-to-strength ratio) and ease of manufacturing

qualities.

• Gypsum plasterboard was used widely throughout the system for its

significant fire performance qualities.

• Bolted connections were used for all large (high load bearing) section-to-

section connections for its simple and ease of assembly qualities.

A brief proposal of design concepts to address multi-storey configurations followed.

Chapter 5 concluded with the need to further investigate the proposed conceptual

design before implementation into real world practice.


6.6 RECOMMENDATIONS AND FUTURE RESEARCH

There is yet to exist a statutory standards specification document for the design of

MBSs. This lack of specifications is likely to leave designers weary of employing

modular construction methods in their projects and thus, is not favourable for

increasing the market share for modular construction. It is recommended that a

statutory standards specification document for MBSs is developed immediately to help

improve the popularity of the modular construction method.

Few studies on the structural behaviour of MBSs currently exist. The need to

understand the structural behaviours of MBSs is great, especially with regards to the

structural behaviours of individual modules and their interactions as a collective

assembly. It is recommended that further investigation of the following structural

aspects are investigated:

• Structural interaction and behaviour of multi-storey modular building

systems – minimal knowledge is understood about the complex behaviour

between the individual modules.

• Fire performance of modular building systems made of steel sections – as

highlighted in the Grenfell Tower Fire incident, fire safety of steel structures

is of utmost importance.

• Development of innovative connections for modular building systems – the

connections of modular building systems heavily influence the structural

behaviour and constructability of the systems.

• Development of advanced corner supported modular building systems –

there exists a great desire for corner supported modular building systems

because they make possible large open space configurations.

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