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Transcript of Steel Building Member Requirement Final
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Bangladesh Steel Re-Rolling Mills Ltd.
Report on
Requirement of Rolled Steel W Shapes
for Multistoried Steel Building in
Bangladesh
Prepared by
Dr. Khan Mahmud Amanat
Professor, Dept. of Civil Engg., BUET
December 2014
Rev. 02
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Executive Summary
Bangladesh Steel Re-rolling Mills Ltd. (BSRM) is installing a rolling mill to
produce structural steel shapes good for construction of multistoried steel buildings in
Bangladesh. Before initiating the production of rolled steel shapes, it is essential to
assess the possible requirements of sizes and dimensions of structural steel shapes,
more specifically wide flange shapes (W shapes), which may be more in demand than
other shapes. With this objective, a detailed numerical finite element study has been
performed on several typical steel building models ranging from 10 storied to 25
storied configurations suitable for Dhaka City. Based on the investigation it has been
found that up to 20-storied buildings, the structural framing can be managed with rolled
W-shapes of depth 16 inch (406 mm) or lower. For a 25 storied building, except for a
few column elements at lower floors, most of the members can be managed with rolled
shapes having depth 16 inch or lower. For the columns of lower floors of 25 storied
building, built-up sections can be a solution. Type of floor system does not have any
effect of the framing requirement of the main structural framing system consisting of
columns, girders (beams connecting the columns) and bracings. When only floor
systems are compared, open-web joist system can achieve about 25% ~ 30% economy
in steel material compared to steel profile deck system. Solid concrete composite slab
system can achieve about 20% ~ 25% economy. However, issues like cost of fabrication,
quality control and additional lead time required should also be taken into
consideration before making final decision about the floor system. When overall steel
material requirement is compared, open-web joist system can achieve about 9%
economy. In such a case, solid concrete composite slab may achieve about 8% economy.
Thus the difference in material economy between solid concrete composite slab and
open-web joist system is marginal. The average weight of structural steel has been
found to vary between 76 kg/m2 to 109 kg/m2 for 10 to 25 storied buildings
respectively depending on type of floor system used. In this study, floor-to-floor height
has been assumed as 12 ft (3.66m). If floor height is reduced to 11 ft (3.35m) then an
additional 3~4% overall economy in material may be achieved.
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Table of Contents
Page
1. INTRODUCTION 1
2. SCOPE OF STUDY 1
2.1 Steel Shape 1
2.2 Material 1
2.3 Maximum Size of W Shapes 1
3. CODES AND STANDARDS 24. LOADING 2
4.1 Dead Loads 2
4.2 Live Load 3
4.3 Wind Load 3
4.4 Earthquake Load 3
5. GENERAL BUILDING CONFIGUARTION 4
5.1 Plan Area 4
5.2 Frame Grid Pattern 4
5.3 Stairs and Lifts 5
5.4 Floor System 5
5.4.1 Concrete Filled Profiled Composite Steel Deck on W-Shaped Floor Beams 5
5.4.2 Solid Concrete Composite Slab on W-Shaped Floor Beams 6
5.4.3 Concrete Slab on Open-Web Joists 7
5.5 Data for Floor Systems 8
5.6 Lateral Load Resisting Elements 8
5.7 Number of Storeys and FLoor Height 8
6. FINITE ELEMENT ANALYSIS 9
6.1 Modeling 9
6.2 Analysis and Design 9
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7. STRUCTURAL SHAPE REQUIREMENTS 10
7.1 Columns 10
7.2 Girders 127.3 Floor Beams 14
7.4 Bracings 14
7.5 Overall Material Requirement 15
8. CONCLUSIONS 17
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1. INTRODUCTION
Bangladesh Steel Re-rolling Mills Ltd. (BSRM) is installing a rolling mill to
produce structural steel shapes good for construction of multistoried steel
buildings in Bangladesh. Before initiating the production of rolled steel shapes, it is
essential to assess the possible requirements of sizes and dimensions of structural
steel shapes, more specifically wide flange shapes (W shapes), which may be more
in demand than other shapes. This report represents a brief study and investigation
carried out to assess the W shape requirement for multistoried buildings in the
context of Bangladesh and more specifically for the capital Dhaka city.
2. SCOPE OF STUDY
2.1 STEEL SHAPE
A steel building requires steel sections of various sizes and shapes which
include angles, tees, channels and the more common wide flange shapes (W
shapes). In a typical steel building, the main load carrying structural frame
elements, e.g. columns and beams etc., usually consists of W shapes. Therefore, the
present study has been confined to the investigation of required W shapes.
2.2 MATERIAL
While the 36 grade A36 steel (F y = 36 ksi or 250 MPa) has been the most
common material for the last few decades, higher strength steel like ASTM A572
grade 50 steel (F y = 50 ksi or 345 MPa) are now becoming more commonplace.Grade 50 steel provides higher strength and more economy than the vintage A36
steel. In this study Grade 50 steel has been the chosen material.
2.3 MAXIMUM SIZE OF W SHAPES
Presently, due to the limitation of proposed the rolling mill, the maximum
achievable depth of the rolled section is about 406mm or 16 inch. Therefore, this
study is also confined with the W shapes having maximum depth of 16 inch or
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about 406mm. Within this limitation, the W shapes contained in the AISC Steel
Construction Manual 13th Edition has been included in the study.
3. CODES AND STANDARDS
It is expected that the updated and revised version of Bangladesh National
Building Code namely BNBC 2010 shall be published soon. Therefore, in the present
study, the provisions of the BNBC 2010 has been adopted. In addition, the
provisions of AISC Specification 2005 is also considered.
4.
LOADING
A rational estimation of loading is very important in such a study involving
building analysis and design. In the present study, the assumed loads are discussed
below.
4.1 DEAD LOADS
Dead loads (D) are those gravity loads which remain acting on the structurepermanently without any change during the structures normal service life. These
are basically the loads coming from the weight of the different components of the
structure. For the sake of convenience in the analysis, sometimes this kind of loads
are divided into two types, namely a) self weight of the structure (SW) and b) the
weight coming from the non-structural permanent components of the building
(DL). In buildings, the weight of floors, beams, columns etc. which form the main
structural system is considered as the self weight (SW). The weights of floor finish,
partition walls and other non-structural permanent components generally
constitute the rest of the total dead load. In this study, following are the values of
dead loads considered in the present analysis.
Reinforced concrete unit weight = 150 lb/ft 3 (2400 kg/m3)
Plain concrete unit weight = 120 lb/ft 3 (1920 kg/m3)
Floor finish (FF) = 25 lb/ft 2
(1.2 kN/m2
)
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Partition wall load= 60 lb/ft 2 (2.87 kN/m2)
4.2 LIVE LOAD
Live load is the gravity load coming from the non-permanent objects like
furniture, human etc. The value of this load has been taken as 60 lb/ft 2 (2.87
kN/m2)
4.3 WIND LOAD
Bangladesh is typically a storm prone area where due consideration to the
thrust due to storm must be given in the analysis and design of building and
structures. Wind load due to storm is typically modeled as lateral thrust force
tending to cause sway or overturning of the building. Detailed specifications on
wind loading on buildings are outlined in BNBC. The present project is located in
central Dhaka for which the following basic parameters are used in wind load
calculation,
Basic wind speed, V b= 65 m/s (145 mph) 3-sec. gust.
Exposure category = A (urban area)
Structure Importance coefficient = 1.0
4.4 EARTHQUAKE LOAD
Proper structural design of any building structure must include loads due to
earthquake shaking. For earthquake resistant structural design, it is essential that
the specific design code be followed. In the current project, Equivalent Static Force
Method of BNBC (2010) is followed for the general design of the building. The
specific parameters relevant for the study are as follows,
Site Class: SD
Seismic Zone co-efficient: 0.2
Structure Importance Factor: 1.0
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Building Type: Steel Moment Frame
Response Modification Factor: 6.0
Seismic Design Category: D
Seismic Design Type: IMF
5. GENERAL BUILDING CONFIGUARTION
5.1 PLAN AREA
The study aims at assessing the general W shape requirement for commoncommercial type of building construction in Dhaka City. In Dhaka City, typical
commercial plots are generally of the size of 12 katha (803 m 2) to 20 katha (1338
m2). Considering the RAJUK requirements and rules, typical area of a floor of such a
building shall range between 4000 sq.ft (372 m2) to 8000 sq.ft (744 m2). Therefore,
the building models studied in this investigation typically have floor areas in this
range.
5.2
FRAME GRID PATTERN
Since this is more of a theoretical study, a regular and rectangular plan grid
pattern for columns has been followed. In a typical commercial building, the column
grid pattern is generally governed by car parking requirements. According to
RAJUK rules, the minimum clear gap between columns shall be 15’-8” (4.78 m) for
two cars and 23’-0” (7.01 m) for three cars. Considering the column size and
cladding, the most practical center-to-center spacing between columns may be 18’-
0” x 26’-0” (4.78m x 7.01m). In the present study, this basic column grid spacing has
been adopted.
With the above basic grid pattern, two types of plans are considered, (a) a 3-
span by 3-bay floor having overall 54’ x 78’ = 4212 sq.ft (392 m2) plan area and (b)
4-span by 4-bay floor having overall 72’ x 104’ = 7488 sq.ft (696 m2) plan area.
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5.3 STAIRS AND LIFTS
Two stairs (one regular and one emergency) and three lifts has been
considered in the plan of the buildings studied.
5.4 FLOOR SYSTEM
A commercial steel building can have many different types of floor systems.
Presently the following three are most popular,
Concrete Filled Profiled Composite Steel Deck on W-Shaped Floor Beams
Solid Concrete Composite Slab on W-Shaped Floor Beams
Concrete Slab on Open-Web Joists.
There are some other proprietary composite open-web joist systems as well like
Hambro Composite Open-Web joist, Vulcraft system etc.
5.4.1 Concrete Filled Profiled Composite Steel Deck on W-Shaped Floor
Beams
A typical example of profiled steel deck floor system are shown in Fig.1
below.
Fig.1 5.4.1 Concrete Filled Profiled Composite Steel Deck
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This type of floor system is very common despite the fact that this is not the
most economical type. Some advantages of such floor system is greater durability,
flexible design, easy on-site handling, speedy and safe construction, easier quality
control, greater reliability etc. which sometimes become more important that just
economy. In this type of floor system, the concrete generally requires only
temperature and shrinkage reinforcement. Typical amount of such concrete
reinforcing steel is of the order of about 4.0 kg/m2 of floor area.
5.4.2 Solid Concrete Composite Slab on W-Shaped Floor Beams
A typical example of solid concrete composite floor system are shown inFig.2 below.
Isometric Typical section
Fig.2 Solid Concrete Composite Slab
Solid RC composite deck is another popular option for floor system in steelstructure and generally yields better economy that the profile deck system in terms
of material requirement. However, such construction requires separate removable
formwork which may be labor and time intensive. At the same time, more intensive
quality control measures must be enforced at site to ensure the safety and
reliability. The reinforced concrete slab also needs structural reinforcement.
Typical amount of such concrete reinforcing steel is of the order of about 8.0 kg/m2
of floor area.
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5.4.3 Concrete Slab on Open-Web Joists
Open-web joists supporting concrete slabs is by far the most economical of
all types floor systems in terms of material requirement which are in general use in
steel buildings. A typical example of open-web system is shown in Fig.3
Fig.3 Open-web Joist System.
The principal advantage of open-web joist system is its economy compared to the
other systems. Another big advantage is that on extra space is required for utility
services e.g. plumbing and air conditioning ducts which helps reducing the overall
floor height. Reduction in floor height ultimately results in economy in the overall
frame design. On the other hand, high level of quality control measures are needed
to ensure the proper fabrication of the joists which also involve welding process.
Fabrication of joists may also require additional lead time. The reinforced concrete
slab also needs structural reinforcement. Typical amount of such concrete
reinforcing steel is of the order of about 10.0 kg/m2 of floor area.
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5.5 DATA FOR FLOOR SYSTEMS
In the present investigation all the three types of floor system described in
the preceding paragraphs are considered. For the concrete filled profiled deck, it is
assumed that the deck is supported and integrally connected by means of shear
studs on W shaped floor beams. The deck material is 1.4 mm thick steel profile. The
overall depth of the concrete fill deck is 6 inches (150 mm) with 3 inch (75mm)
corrugation (amplitude) in the steel profile. The corrugations are 6 inch (150mm)
on centers. For the solid slab composite deck and open-web system the slab
thickness is assumed to be 100mm (4 inch).
5.6 LATERAL LOAD RESISTING ELEMENTS
Pure moment frame steel buildings are generally not very economic. Some
sort of bracing arrangements must be used in a steel building to achieve an
economic solution. There are several proven types of bracing arrangements such as
cross diagonals, concentric K brace, eccentric K brace, steel plate shear wall etc.
Among these, the concentric K brace is one of the most adopted systems in steel
buildings. It is also one of the few approved system of bracings by AISC standard. In
the present investigation concentric K bracing system has been adopted as the
lateral load resistant system.
5.7 NUMBER OF STOREYS AND FLOOR HEIGHT
Though a building as high as 38 storeys exists in Dhaka City, height of typical
commercial buildings ranges between ten to twenty-five stories. In the present
study buildings having 10, 12, 16, 20 and 25 storeys has been considered. A 3-spanby 3-bay floor (overall 54’ x 78’ plan area) has been used for the first four buildings
while 4-span by 4-bay floor (overall 72’ x 104’ plan area) has been used for the 25
storied building.
The floor-to-floor height has been assumed to be 12’-0” (3.66 m) considering
the typical plumbing and duct requirements for air conditioning etc.
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6. FINITE ELEMENT ANALYSIS
6.1
MODELING
Method of structural analysis has a significant impact on the final design of a
building in terms of safety and economy. Depending on the type of project, there are
several well-established methods among which Finite Element Method (FEM) is
perhaps the most sophisticated and all-encompassing one. For the present study,
powerful and popular finite element software package ETABS has been employed
for the structural analysis and design.
A full three dimensional model of the building was developed using frame
and shell elements. The frame elements are typical two-noded space frame
elements having six degrees of freedom per node – three translations and three
rotations in three mutually perpendicular axes system. The plate elements are of
rectangular (or quadrilateral) shape. The rectangular (or quadrilateral) element has
four nodes at its four corners. Each node has six degrees of freedom – three
translations and three rotations in a 3D space configuration. The frame elements
are used to model the beams, columns and braces while the shell elements are used
to model the floor deck. At base level, all nodes were restrained against translation
in any directions (hinges).
A typical 3D view of the 20-storied model is shown in Fig.1 followed by a
plan in Fig.2. The plan shown in Fig.2 has been used for models having 10 ~ 20
floors. Fig.3 shows the typical K-bracing arrangements for the 20-storied model.
Fig.4 shows the plan of 25-storied model.
6.2 ANALYSIS AND DESIGN
Analysis of the building models and the design of the frame members are
performed inside the ETABS software. A typical deflected shape of the 20-storied
model under lateral earthquake load is shown in Fig.5.
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Design of the frame members are performed by ETABS in accordance with
the design criteria mentioned earlier in this report. It may be mentioned that one of
the principal objective of steel structure design is to obtain the minimum weight
while maintaining the code provisions and safety. Therefore, arriving at the most
optimum design is not a straight forward task. Rather it involves a trial and error
procedure where several successive trail runs are required to arrive at the best
possible balanced between safety and economy. In the present investigation, design
close to the optimum condition confirming the least possible weight of structural
members are obtained for each of the buildings through several trail runs of
analysis and design.
7. STRUCTURAL SHAPE REQUIREMENTS
Based on the analysis and design procedure mentioned above, the structural
design requirements for various elements like columns, beams etc. are summarized
in the following sections.
7.1
COLUMNS
Maximum required size of W shapes adequate for the columns are given in
the following tables 1 through 5 for 10, 12, 16, 20 and 25 storied buildings. It can be
observed from the Tables 1 through 5 that except the edge columns of 25 storied
build, all other columns are of 16 inch depth or smaller. For the columns of the 25
storied building at lower levels, bigger sections or built-up sections may provide a
solution. However, a further study is required to get a better insight on this issue.
Table 1: W Shape requirements for columns of 10 storied building.
Concrete Filled
Profiled Steel
Deck
Solid Concrete
Composite Deck
Slab
Open-web Joist
System
Corner Column W12x58 W12x58 W12x58
Edge Column W12x152 W12x152 W12x152
Interior Column W12x136 W12x136 W12x136
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Table 2: W Shape requirements for columns of 12 storied building.
Concrete Filled
Profiled Steel
Deck
Solid Concrete
Composite Deck
Slab
Open-web Joist
System
Corner Column W14x68 W14x68 W14x68
Edge Column W12x190 W12x190 W12x190
Interior Column W12x170 W12x170 W12x170
Table 3: W Shape requirements for columns of 16 storied building.
Concrete Filled
Profiled SteelDeck
Solid Concrete
Composite DeckSlab
Open-web Joist
System
Corner Column W12x152 W12x152 W12x152
Edge Column W12x210 W12x210 W12x210
Interior Column W12x210 W12x210 W12x210
Table 4: W Shape requirements for columns of 20 storied building.
Concrete Filled
Profiled Steel
Deck
Solid Concrete
Composite Deck
Slab
Open-web Joist
System
Corner Column W12x230 W12x230 W12x230
Edge Column W12x252 W12x252 W12x252
Interior Column W12x230 W12x230 W12x230
Table 5: W Shape requirements for columns of 25 storied building.
Concrete FilledProfiled Steel
Deck
Solid ConcreteComposite Deck
Slab
Open-web JoistSystem
Corner Column W14x159 W12x170 W12x170
Edge Column W12x279** W12x279** W12x279
Interior Column W12x279** W14x233 W12x279
**Sizes greater than these are required or built-up section may be used
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7.2 GIRDERS
Maximum required size of W shapes adequate for the girders (beams
connecting the columns) are given in the following tables 6 through 10 for 10, 12,
16, 20 and 25 storied buildings. It can be observed from the Tables 6 through 10
that all beam sections are of 16 inch depth or smaller.
Table 6: W Shape requirements for girders of 10 storied building.
Concrete Filled
Profiled SteelDeck
Solid
ConcreteComposite
Deck Slab
Open-web
JoistSystem
Edge girder short direction W10x49 W10x49 W10x49
Edge girder long direction W14x30 W14x30 W14x30
Interior girder short direction W10x49 W10x49 W10x49
Interior girder long direction W16x40 W16x40 W16x40
Table 7: W Shape requirements for girders of 12 storied building.
Concrete Filled
Profiled Steel
Deck
Solid
Concrete
Composite
Deck Slab
Open-web
Joist
System
Edge girder short direction W10x49 W10x49 W10x49
Edge girder long direction W16x31 W16x31 W16x31
Interior girder short direction W10x49 W10x49 W10x49
Interior girder long direction W14x48 W14x48 W14x48
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Table 7: W Shape requirements for girders of 16 storied building.
Concrete Filled
Profiled Steel
Deck
Solid
Concrete
Composite
Deck Slab
Open-web
Joist
System
Edge girder short direction W8x48 W8x48 W8x48
Edge girder long direction W16x26 W16x26 W16x26
Interior girder short direction W10x49 W10x49 W10x49
Interior girder long direction W16x50 W16x50 W16x50
Table 9: W Shape requirements for girders of 20 storied building.
Concrete Filled
Profiled Steel
Deck
Solid
Concrete
Composite
Deck Slab
Open-web
Joist
System
Edge girder short direction W16x100 W16x100 W16x100
Edge girder long direction W16x31 W16x31 W16x31
Interior girder short direction W12x53 W12x53 W12x53
Interior girder long direction W16x50 W16x50 W16x50
Table 10: W Shape requirements for girders of 25 storied building.
Concrete Filled
Profiled Steel
Deck
Solid
Concrete
Composite
Deck Slab
Open-web
Joist
System
Edge girder short direction W14x99 W14x99 W14x99Edge girder long direction W16x40 W16x40 W16x40
Interior girder short direction W12x53 W12x53 W12x53
Interior girder long direction W16x89 W16x89 W16x89
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7.3 FLOOR BEAMS
Floor beams are the beams supporting the floor deck and transferring the
load to the girders. The floor beams are modeled as simply supported beams resting
on girders and transferring the gravity load to the girders. Since the basic floor
panel size is same (18' x 26') for all buildings, the size of the floor beam is also same
for each type of floor system. Table 11 shows the required maximum size of floor
beams for each type of floor system.
Table 11: Floor beam/joist requirements for buildings.
Concrete Filled ProfiledSteel Deck
Solid ConcreteComposite Deck Slab
Open-web Joist System
W12x14 W10x22 20LH09
7.4 BRACINGS
In this study, concentric K-bracing system has been adopted for the building
models. The maximum size of required W shapes for K-braces are given in Table 12
that follows. In Table 12 it may be observed that requirement for 20 storiedbuilding (W8x48) is lower than the requirement of 16 storied building (W16x67).
This is due to the fact that, in the 16 storied building, K-bracing system has been
applied to only one bay per side while in the 20 storied building, it was two bays
per side. Thus the bracing in the 20 storied building had stronger configuration
resulting in a smaller section requirement.
Table 12: W Shape requirements for K-bracing system.
Concrete Filled
Profiled Steel Deck
Solid Concrete
Composite Deck Slab
Open-web
Joist System
10 storied building W12x45 W10x45 W10x45
12 storied building W10x49 W10x49 W10x49
16 storied building W8x40 W8x40 W8x40
20 storied building W8x48 W8x48 W8x48
25 storied building W14x74 W12x65 W12x65
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7.5 OVERALL MATERIAL REQUIREMENT
The average material requirement per unit floor area is a very important
parameter in making decision about a building project. In the present investigation,
the average weight of steel requirement for different buildings having different
floor systems are given in the following Tables 13 through 15.
Based on the material requirement the average steel requirement per unit
floor area has been determined and presented in Table 16. In this table an
additional 10% allowance in weight is considered to include the weight of
accessories like splice plates, gusset plates, connections, bolts etc.
Table 13: Element wise material requirement for buildings with profile steel deck floor system
Material 10-Storey 12-Storey 16-Storey 20-Storey 25-Storey
Area per floor, m2 392 392 392 392 696
Total area, m2 4312 5096 6664 8232 18096
Column weight, ton Steel 82 115 171 256 551
Girder weight, ton Steel 116 146 177 249 536
Brace weight, ton Steel 21 27 62 86 144
Floor beam, ton Steel 57 66 86 106 190
Floor weight, ton Conc 1234 1484 1908 2357 4723
Rebar for concrete, ton Steel rebar 16 19 26 32 70
Metal deck weight, ton Steel 44 52 68 84 193
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Table 14: Element wise material requirement for buildings with solid concrete composite slab floor system
Material 10-Storey 12-Storey 16-Storey 20-Storey 25-Storey
Area per floor, m2 392 392 392 392 696
Total area, m2 4312 5096 6664 8232 18096
Column weight, ton Steel 80 115 171 254 550
Girder weight, ton Steel 115 144 195 260 510
Brace weight, ton Steel 22 27 62 86 140
Floor beam, ton Steel 59 66 87 115 240
Floor weight, ton Conc 1234 1460 1908 2356 4200
Rebar for concrete, ton Steel rebar 31 36 47 58 127
Metal deck weight, ton Steel None None None None None
Table 15: Element wise material requirement for buildings with open-web joist floor system
Material 10-Storey 12-Storey 16-Storey 20-Storey 25-Storey
Area per floor, m2 392 392 392 392 696
Total area, m2 4312 5096 6664 8232 18096
Column weight, ton Steel 79 115 171 252 556
Girder weight, ton Steel 115 144 176 244 518
Brace weight, ton Steel 21 26 62 86 135
Floor beam, ton Steel 45 65 73 80 189
Floor weight, ton Conc 1234 1484 1908 2356 4200
Rebar for concrete, ton Steel rebar 39 46 60 74 163
Metal deck weight, ton Steel None None None None None
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Table 16: Average steel requirement per unit floor area, kg/m2.
No. of Storeys
Concrete Filled
Profiled Steel Deck
Solid Concrete
Composite Deck Slab
Open-web Joist
System
10 85.7 78.3 76.3
12 91.7 83.8 85.5
16 97.4 92.8 89.5
20 108.6 103.3 98.3
25 102.4 95.3 94.9
8. CONCLUSIONS
A detailed numerical finite element investigation has been performed to
study the rolled W shape requirement for typical steel commercial buildings in
Dhaka City. Detailed findings of the study are presented in the preceding articles.
The scopes and assumptions of the study are also mentioned in detail in the
preceding sections. The study mainly focuses on the steel material requirement of
the main structural members and components. No consideration is given to
construction related issues or effect of non-structural building components on
costing. The results of this investigation should be interpreted in the context of
these scopes and assumptions. Based on the study, following conclusions can be
drawn.
Up to 20-storied buildings, the structural framing can be managed with rolled
W-shapes of depth 16 inch (406 mm) or lower.
For a 25 storied building, except for a few column elements at lower floors, most
of the members can be managed with rolled shapes having depth 16 inch or
lower. For the columns of lower floors of 25 storied building, built-up sections
can be a solution.
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Type of floor system does not have any effect of the framing requirement of the
main structural framing system consisting of columns, girders (beams
connecting the columns) and bracings. Regardless of the floor system adopted,
the structural and material requirement for these framing elements are
generally the same.
Open-web joist type floor system results in the most economical solution in
terms of material requirement. However, issues like cost of fabrication, quality
control and additional lead time required should also be taken into
consideration before making final decision about the floor system.
When only floor systems are compared, open-web joist system can achieve
about 25% ~ 30% economy in steel material compared to steel profile deck
system. Solid concrete composite slab system can achieve about 20% ~ 25%
economy.
When overall steel material requirement is compared, open-web joist system
can achieve about 9% economy. In such a case, solid concrete composite slabmay achieve about 8% economy. Thus the difference in material economy
between solid concrete composite slab and open-web joist system is marginal.
The average weight of structural steel has been found to vary between 76 kg/m2
to 109 kg/m2 for 10 to 25 storied buildings respectively depending on type of
floor system used.
In this study, floor-to-floor height has been assumed as 12 ft (3.66m). If floor
height is reduced to 11 ft (3.35m) then an additional 3~4% overall economy in
material may be achieved.
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Fig.1 3D view of the finite element model of 20 storied building
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Fig.2 Plan of 10 ~ 20 storied models
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Fig.3 Elevation of 20-storied building showing bracing arrangements.
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Fig.4. Plan of 25-storied model
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Fig.5 Typical deflected shape of 20-storied model under lateral load.
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Fig.6 Typical W-Shape requirements for the lower floor of the 20-storied building.