Structure and Architectural Form of Tall Buildings

Mahjoub Elnimeiri, PhD, PE, MASCE

Chairman cdci engineers international & Professor at IITMember of steering group, CTBUH

Chicago, USA

World Map

World’s Tallest Buildings Chart

Meter

1000

900

800

700

600

500

400

300

200

100

0

Impact of 9/11 on Tall Building Construction

structure20-30%

MEP20-25%

elevator system6-12%

architecture30-40%

Structural Economy, Efficiency and ConstructabilityCost of Structure in relation to Total Construction Costs

Dubai, 1991

Dubai, 2003

Dubai, 2007

Dubai, 2007

Dubai, 2003

Dubai, 2007

Dubai, 2008

Dubai, 2008

Dubai, 2008

Dubai, 2008

Dubai, 2003

Dubai, 2008

DUBAI TOWERS AT THE LAGOONArchitect : TVS, Engineer : CDCi

Tower29

SITE PLAN

Tower29 HEIGHT BUILT-UP AREA

TOWER-01 360 m 120,000 sq. m

TOWER-20 410 m 140,000 sq. m

TOWER-21 460 m 160,000 sq. m

TOWER-29 550 m 210,000 sq. m

PLAN LAYOUT

ATRIUMS

FAÇADE DETAIL

TOWER SPIRE

GROUND LEVEL VIEW

Height Built-up Area

Tower-01 550 m 120,000 sq. m

Tower 20 140,000 sq. m

Tower 21 160,000 sq. m

Tower 29 360 m 210,000 sq. m

SPECIAL CONSIDERATIONS

• Scale, Height

• Iconic Form: Twisting and Plan Morphing

• Location: “DUBAI”

• Grouping

• Constructability

STRUCTURE OBJECTIVE

• Preserve the Architectural Vision

• Maintain the Structural Integrity

PRELIMINARY STRUCTURAL DESIGN CRITERIA

• Dynamic Impact of Wind: Wind-Tunnel, Simulation, etc.

• Human response/ comfort

• Load Path: impact of geometry

• Progressive Collapse analysis (redundancy)

• Differential shortening: Composite Materials, Temperature, etc.

• Construction Sequencing

• Connectivity with Exterior

STRUCTURAL COMPOSITE SYSTEM

• Exterior Twisted Braced Tube

• Core RC Shear Wall

• Out- riggers/ Belt Trusses

• Typical Composite Floor

• Interaction between vertical and horizontal loadings

• Appreciable movement both horizontally and downwards

• Strategy to ensure stability and stiffness

LOAD PATH : IMPACT OF GEOMETRY

Progressive Collapse analysis (redundancy):

WIND FLOW AROUND A TALL BUILDING

OVERALL LOADING & DYNAMIC RESPONSE

Cross-wind vibrations are usually greater than along-wind vibrations for buildings of heights greater than 100m (330 feet)

along wind

cross wind

CROSS WIND CONCERNS

- Accelerations beyond acceptable human tolerance

- Excessive Bending moments and shear forces

TORSIONAL LOADING AND RESPONSE

Two mechanisms :

• Applied moments from aerodynamic forces produced by non-uniform

pressure distributions or non-symmetric cross-sections

• Structural eccentricity between elastic center and geometric center

INTERFERENCE EFFECTS

Surrounding buildings can produce increases or decreases in peak wind loads :

Shows percentage change in peak cross-wind response of building B, due to a similar building A at position (X,Y)

10b 8b 6b 4b 2b -2bb

Building B

Wind direction

(X,Y)

Building A

V

b

2b

3b

4b

0%

+30%

+20% +10%

-10%

+10%

+20%

X

Y

0%-20%

increases increases

decreases

AUXILIARY DAMPING

Visco-elastic Damper

used on World Trade Center buildings, New York

F/2 F/2

Steel flange

V.E. material

Centreplate

F

used on City Corp Building, New York (M2=400 ton of concrete)

K

CM

K

CM

yy

1

11

2

22

21 (t) (t)

AUXILIARY DAMPING

Tuned-mass Damper

used on Shin-Yokohama hotel, Japan

h

2R

AUXILIARY DAMPING

Tuned-liquid (sloshing) Damper

SHAPING BUILDINGS TO REDUCE AERODYNAMIC EXCITATION & RESPONSE

• Determination of cross-wind response

• Controlling the cross-wind force spectrum

PARAMETRIC STUDY

• Tapering

• Softening the edge in plan

• Porosity

• Twisting

• Plan Morphing

FORM GENERATION PROCESS

1. Morph 2. Taper 3. Twist

MODEL MAKING

PHYSICAL MODELS

c. Architectural Modelb. Structural Modela. Structural Sketch

CONSTRUCTION SEQUENCE

CONSTRUCTION SEQUENCE

CONSTRUCTION SEQUENCE

CONSTRUCTION SEQUENCE

CONSTRUCTION SEQUENCE

CONSTRUCTION SEQUENCE

CONSTRUCTION SEQUENCE

CONSTRUCTION SEQUENCE

TWIST…DOUBLE SPIRAL BRACE…TAPERED…ECCENTRIC TWIST-REVERSING

Displacements : WLX Whole

Fx : DL+LL Fx : 1 DL+LL Fx : WLX

Displacements : DL+LL Displacements : DL+LLBrace diagram Displacements : DL+LL Displacements : DL+LL Displacements : WLX Displacements : Whole

Whole Structure Fx : DL+LL Fx : DL+LL Fx : WLX Fx : Whole

AXIAL FORCES IN STRUCTURAL ELEMENTS

Due To Gravity Load Due to Wind Load

STRUCTURAL BEHAVIOUR UNDER GRAVITY LOADS

Axial Forces Bending Moments

ELEMENTS OF THE STRUCTURAL SYSTEM

OUTRIGGERS FLOORS 38-42

PRELIMINARY SECTION PROPERTIES

SHEAR WALL THICKNESS AND CONFIGURATION

BUILDING SECTION AND STRUCTURAL MODEL FOR PRELIMINARY ANALYSIS

INTERIOR COLUMNS

SUMMARY OF TYPICAL STATIC LOADS

STATIC WIND LOADING DIAGRAM

PRELIMINARY DRIFT RATIO ANALYSIS

Shear Wall Alone Exterior Frame Only

PRELIMINARY DRIFT RATIO ANALYSIS

Shear Wall + Exterior Frame Shear Wall + Exterior Frame + Outriggers

TIP DEFLECTION AND DRIFT RATIO

Def = 0.60Drift ratio = 733 @ Level 100

Def = 0.56Drift ratio = 786 @ Level 100

Wind X Wind Y

EFFECTS OF TWIST ON SLAB DUE TO SHEAR STRESSES

3D ViewPlan

EFFECTS OF TWIST ON SLAB DUE TO SHEAR STRESSES

Shear Forces at Slabs

AXIAL FORCES DUE TO DEAD LOADS

Shear Wall Exterior Frame

tensioncompression

SUPPORT REACTIONS AT GROUND LEVEL

AXIAL FORCES DUE TO WIND ‘X’

compression tension

Shear Wall Exterior Frame

AXIAL FORCES DUE TO WIND ‘Y’

compression tension

Shear Wall Exterior Frame

AXIAL FORCES @ BASE DUE TO DEAD LOAD (KN/mm)

AXIAL FORCES @ BASE DUE TO DEAD LOAD + LIVE LOAD (KN/mm)

AXIAL FORCES @ BASE DUE TO DEAD LOAD + WIND LOAD (KN/mm)

AXIAL FORCES DUE TO STRUCTURAL OWN WEIGHT (KN/mm)

Shear Wall Exterior Frame

AXIAL FORCES DUE TO TOTAL DEAD LOAD (KN/mm)

Shear Wall Exterior Frame

AXIAL FORCES DUE TO TOTAL DEAD + LIVE LOAD (KN/mm)

Shear Wall Exterior Frame

AXIAL FORCES @ BASE OF EXTERIOR FRAME

Due To Dead Load Due to Wind Load

BENDING MOMENTS @ BASE OF EXTERIOR FRAME

Due To Dead Load Due to Wind Load

SUPPORT REACTIONS

SUPPORT REACTIONS

SUPPORT REACTIONS

HORIZONTAL REACTION COMPONENTS @ BASE

CONCEPTUAL LOAD TRANSFER FROM TOWER TO GROUND

bedrock

bedrock

1.2-1.6m