structure and architectural form of tall buildings - … and architectural form of tall buildings...
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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
structure20-30%
MEP20-25%
elevator system6-12%
architecture30-40%
Structural Economy, Efficiency and ConstructabilityCost of Structure in relation to Total Construction Costs
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
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):
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
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
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
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