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Design of Slender Tall Buildingsfor Wind & Earthquake
.
Regency Steel Asia Symposium on Latest Design & ConstructionTechnologies for Steel and Composite Steel-Concrete Structures09 July 2015
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Structural Design Challenges for Tall Buildings
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Balancing structural needs vs. project demands are always a challenge ..specially for
tall buildings.
Developers Requirements
Architectural Vision
Construction ConstraintsStructural NeedsOthers?
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h
w
w
2h
W
2W
16
M 4M
Short Buildings:
Generally strength governs design Gravity loads predominant
Intermediate Buildings:
Strength / drift governs design Gravity / lateral loads predominant
Tall Buildings:
Generally drift / building motiongoverns design
Lateral loads predominant
Source: CTBUH
Premium for Height
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As buildings get taller, wind-induced dynamic response starts todictates the design.
, (,)
, ()
(00)
() (/)
Wind
Static Loads, A
Low Freq. Background
Comp., B
Dynamic Loads
Resonant Comp., C A,B &C
B &C B &C
A & B : Dependent on building geometry & turbulence environment
C : Dependent on building geometry. turbulence environment &
structural dynamic properties (mass, stiffness, damping)
+
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For many tall & slender buildings cross wind response can govern loading & acceleration.
Wind codes generally cover along-wind responsebased on the Gust Factor Approach
but little guidance on cross-wind & torsional responses.
Wind
EN 1991-1-4 states that for slender buildings(h/d > 4), Wind Tunnel Studies are necessary if
distance between buildings is < 25 x d
natural frequency < 1 Hz.
BCA guidelines: H > 200m or f < 0.2Hz
Prediction of building dynamic properties:natural frequencies, mode shapes & damping
have a great effect on the predicted wind loads& accelerations.
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As an engineer, there are a number of approaches to minimizecross-wind response
orientation
setbacks, varying cross-section
softened corners
twisting, tapering
introducing porosity
Wind
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Tall buildings design often driven by occupant comfortcriteria, i.e., limits to lateral acceleration
Two conditionsare generally important alarmcaused by large motions under occasional
strong winds
annoyancecaused by perceptible motions on aregular basis - more important
Solutions include stiffeningthe building, increasing massor use of supplemental damping.
Occupant Comfort
US Practice,Office
US Practice,Residential
ISO, Office
ISO, Residential
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Many codes specify (& some provide guidelines) fora deflection limit of h/400 ~ h/600.
Drifts can be based on winds of appropriate returnperiod- generally between 10 to 25 year returnperiod winds.
Story drifts have two components:
Rigid body displacement Due to rotation of the building as a whole
No damage
Racking (shear) deformation
Angular in-plane deformation
Creates damage in walls and cladding
Limit can be reviewed if damage to non-structuralelements can be prevented, especially the faade,& lift performance is not affected.
Drift
tall & flexible
short &stiff
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Differential shortening of vertical elements needspecial consideration.
Initial position of slabs can be affected with time- affecting partitions, mechanical equipment,cladding, finishes, etc.
Mitigation options include appropriate stiffness
proportioning, choice of material, verticalcambering, etc..
Differential Shortening
0
-30
-25
-20
-15
-10
-5
00 20 40 60 80
C E
C C
C
N
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Robustness
Which system is better?
Same strength & deformation capacity
What is the impact of premature loss of one element?
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Important to consider constructionsequence & schedules in analysis tocapture effects of:
compressive shortening, creep & shrinkage, &
any locked in stresses fromtransfer beams, outriggersystems, stiffer elements
Becomes more complex on non-symmetric structures where the axialshortening can cause floors to twistand tilt under self weight.
Sequential Analysis
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Tall buildings are big budget projects small savings per sq. m can become largeamounts of money.
Efficiency & economy are not defined by codes.
Custom programs & scripts required to interface directly with commercial structuralanalysis packages to rapidly and efficiently establish optimum element sizes.
Structural Optimization
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Settlement control critical for tall buildings toprevent tilt.
Soil structure interaction analysis may be
required for accurate determination offoundation flexibility.
Thick pile rafts minimize differential settlements.
Foundation Settlements
100
90
80
70
60
50
40
30
20
10
0
0 20 40 60 80 100 120
()
()
A ( ):
= 33.3 16.1 = 17.2
= 102 73 = 29
, = 17.2 / 29,000 = 1 : 16 80 > !
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Structural Systems for Tall Buildings
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Interior Structures
Dual systems - shear wallframe interaction for effectiveresistance of lateral load
Single component resisting systems
Effectively resists bending by exteriorcolumns connected to outriggersextended from the core
Interior Structures: single / dual component planar assemblies in 2 principal directions.
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Exterior Structures
Exterior Structures: effectively resist lateral loads by systems at building perimeter
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Dual System: RC Core + Perimeter Frames
Efficient system using
Central Services Core as the primary system
Coupled with the Perimeter Frame for additional stiffness
Generally economical up to 50 ~ 60 stories.
Marina Bay Financial Centre, Singapore
Per. Columns
Core
Semi-Precast Slab
PT Band Beams
C B
Shear sway Cantilever sway
H = 245m
50 storey
H = 186m
33 storey
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Extremely efficient system: outriggers engage perimeter columns & reduce core overturning moment. Architecturally unobtrusive since outriggers are located at mechanical floor & roof.
Exterior column spacing meets aesthetic & functional requirements, unlike tube systems.
One Raffles Quay, Singapore
H/D = 6.5
50 Storey
H = 245m
Core + Outrigger + Belt Truss
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Four Seasons Place, KL, Malaysia
75 storeyH = 342mH/D=12.5
Podium
Hotel
Residentia
l
Innovative system to address extreme slenderness. Coupled walls extend over entire depth of floor plate to resist overturning moment & shear at every floor.
Coupled Outrigger Shear Walls
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Tornado Tower, Doha, Qatar
Conceived to integrate with architectural form.
Extremely efficient exterior structure suitable for up to 100+ stories.
Variant of tubular systems & exterior braced frames.
Carries gravity & lateral forces in a distributive and uniform manner. .
Effective because theycarry shear by axialaction of the diagonalmembers (less sheardeformation).
Joints are complicated
52 storey, H = 200m
Diagrid
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(23)
(45)
M
Towers with large mass eccentricity - weightsensitive & large movements.
Long-term serviceability challenges.
Structural System: Shear Wall + Rigid Frame+ Outriggers + Belt Truss + Core Coupling
Truss + Internal Braced Truss
Atrium BracedTruss
L36Coupling TrussOutrigger TrussBelt Truss
L12Outrigger TrussBelt Truss
Belt TrussesOutrigger Trusses
79 storey,H = 351m
65 storey,H = 305m
52 storey,H = 251m
Signature Tower, Dubai,
UAE
Hybrid
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Key Considerations for Seismic Design
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Seismic design philosophy focuses on safetyrather then comfort.
For Design Level Earthquakes, structuresshould be able to resist:
Minor shaking with no damage
Moderate shaking with no severe structuraldamage
Maximum design level shaking with
structural damage but without collapse
Tall or small ? Which is safer?
Source: FEMA
Mexico City Earthquake, 1985
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Torsional Irregularity: Unbalanced Resistance
Plan Conditions Resulting Failure Patterns
Re-Entrant Corners
Diaphragm Eccentricity
Non-parallel LFRS
Out-of-Plane Offsets
Source: FEMA
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Vertical Conditions Resulting Failure Patterns
Stiffness Irregularity: Soft Story
Mass Irregularity
Geometric Irregularity
In-Plane Irregularity in LFRS
Capacity Discontinuity: Weak Story
Source: FEMA
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Overview of BC3
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Seismic requirement in Singapore from 1 Apr 2015
Source: Pappin et. al.
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Building height, H > 20m?
NSeismic Action need not be considered in design
Ordinary building on Ground Type Class D or S1, or Special building on Ground Type Class C, D or S1
Drift limitation check according to Clause 7 Minimum structural separation check according to Clause 8
Seismic Action need not be considered in design
Ground Type within building footprint determined according to Clause 2
Y
NY
Seismic Action determined according to Clause 3 & Clause 4, using where appropriate, either Lateral Force Analysis Method according to Clause 4.4, or Modal Response Spectrum Analysis Method according to Clause 4.5
Building analyzed according to combination of actions in Clause 5, and
Foundation design carried out according to Clause 6
Design Flowchart
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l
B C D 1
A
1.0
1.4
> 20
Definitions
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T(sec)
SpectralAcceleration(%g)
T(sec)
SpectralAcceleration(%g)
0.0 4.50 1.8 10.00
0.1 5.25 2.0 9.00
0.2 6.00 2.2 8.18
0.3 6.75 2.4 7.50
0.4 7.50 2.7 6.67
0.5 8.25 3.0 6.00
0.6 9.00 3.5 5.14
0.7 9.75 4.0 4.50
0.8 10.50 4.6 3.91
0.9 11.25 5.2 3.06
1.0 11.25 6.0 2.30
1.1 11.25 7.0 1.69
1.2 11.25 8.0 1.29
1.4 11.25 9.0 1.02
1.6 11.25 10.0 0.83
T(sec)
SpectralAcceleration(%g)
T(sec)
SpectralAcceleration(%g)
0.0 2.88 1.8 4.40
0.1 3.96 2.0 3.96
0.2 5.04 2.2 3.60
0.3 6.12 2.4 3.30
0.4 7.20 2.7 2.93
0.5 7.20 3.0 2.64
0.6 7.20 3.5 2.26
0.7 7.20 4.0 1.98
0.8 7.20 4.6 1.72
0.9 7.20 5.2 1.52
1.0 7.20 6.0 1.32
1.1 7.20 7.0 1.13
1.2 6.60 8.0 0.99
1.4 6.09 9.0 0.88
1.6 4.95 10.0 0.79
T(sec)
SpectralAcceleration(%g)
T(sec)
SpectralAcceleration(%g)
0.0 5.76 1.8 14.40
0.1 6.30 2.0 14.40
0.2 6.84 2.2 14.40
0.3 7.38 2.4 14.40
0.4 7.92 2.7 11.38
0.5 8.46 3.0 9.22
0.6 9.00 3.5 6.77
0.7 9.54 4.0 5.18
0.8 10.08 4.6 3.92
0.9 10.62 5.2 3.07
1.0 11.16 6.0 2.30
1.1 11.70 7.0 1.69
1.2 12.24 8.0 1.30
1.4 12.78 9.0 1.02
1.6 14.40 10.0 0.83
Ground Type DGround Type C Ground Type S1
Design Spectra
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Design Example
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Modal Response Spectrum Analysis Method (Para* 4.5)
The intent of a more rigorous dynamic analysis approach is to more accuratelycapture the vertical distribution of forces along the height of the building. The stepsfor a dynamic analysis are summarized below.
Solve for the buildings period and mode shapes. Ensure sufficient modes are used in the dynamic analysis by inspecting the
cumulative modal participation. Determine base shears obtained through response spectrum in each direction
under consideration.
Determine Design Spectrum (Para* 3.2)
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Modal Response Spectrum Analysis
A response spectrum analysis is then run in two orthogonal directions.
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Modal Response Spectrum Analysis
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Required Combinations of Actions (Load Combinations) (Para* 5.2)
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Building Response
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The Sail @ Marina BaySingapore245m, 70 Story,2008
ConcreteResidential
Capital PlazaAbu Dhabi210m, 45 Story2012Concrete
Residential, Hotel & Office
WTC IIJakarta, Indonesia160m, 30Story,2012Composite
Office
Ocean HeightsDubai310m, 82 Story2010Concrete
Residential
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Nurol Life TowerTurkey250m, 60 Story,Under construction
CompositeResidential & Office
IFC ISGYO Office TowerTurkey111m, 27 Story,Under construction
CompositeOffice
Izmir Ova Centre,Turkey112m, 27 Story,Under construction
CompositeOffice
Thamrin Nine,Jakarta, Indonesia325m, 71 Story,Under construction
CompositeOffice & Hotel
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The 75-storey, 342m tower will be 2nd tallestbuilding in Malaysia when completed in 2017.
Challenging project due to 12.5 slenderness ratio.
WT studies revealed significant wake vortices and
strong cross wind effects.
342.5mFour Seasons Place, KL, Malaysia
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An innovative lateral load resisting system wasdevised incorporating
suitably located fin walls two levels of concrete outrigger and
perimeter belt walls, all coupled with the central core-walls.
Ty = 10.1s Tx = 6.4s Tr = 6.0s
Four Seasons Place, KL, Malaysia
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325m
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360,0002 4
J , J.
71, 325
J 2018.
Thamrin Nine, Jakarta, Indonesia
325m
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Ty = 7.2s Tx = 6.8s Tr = 3.2s
C /C/B/
&
Structural System
Thamrin Nine, Jakarta, Indonesia
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Curvilinear Form + Large Inclinations + Atrium Voids Unique Engineering Challenge
(23)
(23)(45)
4539305
49.1
36.4
248
M
0
Lateral effect due to gravity loads
> 2 times design wind load
Zone 1 EQ
All columns & internal walls curved
Atrium voids throughout height
Extremely weight sensitive
Large building movements
Signature Towers, Dubai
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L4A
A
Signature Towers, Dubai
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L7
Signature Towers, Dubai
Si T D b i
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L10
Signature Towers, Dubai
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Signature Towers, Dubai
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L36A
g ,
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Signature Towers, Dubai
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L46
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Signature Towers, Dubai
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L50
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Signature Towers, Dubai
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L56
Signature Towers, Dubai
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D L D E D
360 160 800H/380H/1890H/840
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,
=
40 40 100 / 200
Ultimate Force
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BS-6399-2 (ult)
EN 1991-1-4 +G.I. (ult)
height,m
height,m
Force (kN) Force (kN)
Notional Load
Notional Load + G.I.
0
50
100
150
200
250
0 300 600
0
50
100
150
200
250
0 300 600
Ultimate Over Turning Moment
,
=
40 40 100 / 200
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0
50
100
150
200
250
0 1500000 3000000
B63992 ()
EN 199114 +G.I. ()
,
,
M. (N) M. (N)
N L
N L + G.I.
0
50
100
150
200
250
0 500000 1000000
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Ultimate Force
,
=
22 70 100 / 200
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B63992 ()
EN 199114 +G.I. ()
,
,
F (N)F (N)
N L
N L + G.I.
0
50
100
150
200
250
0 400 800
0
50
100
150
200
250
0 400 800
Ultimate Over Turning Moment
,
=
40 40 100 / 200
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0
50
100
150
200
250
0 2000000 4000000
BS-6399-2 (ult)
EN 1991-1-4 +G.I. (ult)
height,m
height,m
Overturning Mom. (kN-m) Overturning Mom. (kN-m)
Notional Load
Notional Load + G.I.
0
50
100
150
200
250
0 500000 1000000
Impact of Seismic Loads
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Ultimate Over Turning Moment
,
=
40 40 100 / 200
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0
50
100
150
200
250
0 1000000 2000000 30000000
50
100
150
200
250
0 1000000 2000000
height,m
height,m
Overturning Mom. (kN-m)Overturning Mom. (kN-m)
BS-6399-2 (ult)
EN 1991-1-4 +G.I. (ult)
Notional Load
BC3 Seismic + G.I.
(q = 1.5, Soil Type D)
Notional Load + G.I.
Ultimate Force
,
=
40 40 100 / 200
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0
50
100
150
200
250
0 250 500 7500
50
100
150
200
250
0 200 400 600 800
height,m
height,m
Force (kN)Force (kN)
BS-6399-2 (ult)
EN 1991-1-4 +G.I. (ult)
Notional Load
BC3 Seismic + G.I.
(q = 4.5, Soil Type D)
Notional Load + G.I.
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Cost Comparison of Concrete vs.Composite Tall Building
82% of the 100 tallest buildings are either concrete or composite.
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Comparative Case Study of a Typical Tall Building in Singapore
B D
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B D
GFA: 85,000 2
H: 130
N. F: 30
. F H: 4.3
. F A: 2800 2
C : 15.5
L : D
C C + F
RC Building Steel-ConcreteComposite Building
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Comparative Case Study of a Typical Tall Building in Singapore
Design Criteria
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() :
() : 1.5
() : 3.5 + 1 = 4.5
() : 1.0 ( )
: 22/ M H, 50
: M 1.3
: EN 19981, BC3, =1.5, G D
, : L / 250, 20
, : L / 350
, : L /500, 10
: H / 500
F A: : F 4 H & / A 0.5%
Comparative Case Study of a Typical Tall Building in Singapore
Building Dynamic Properties
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T1 = 3.5 s T2 = 3.1 sRC Building
Composite BuildingT1 = 3.2 s T2 = 2.9 s
Comparative Case Study of a Typical Tall Building in Singapore
Building Performance Comparison
RC Building:
Composite Building:
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RC Building:
Veq1 = 3.41%*W = 35.9 MN
Veq2 = 3.95%*W = 41.6 MN
Sd (T) = Se(T). lq
[l = 1.0, q=1.5]
0
5
10
15
20
25
30
35
0 1000 2000 3000 4000
Storey
Lateral Storey Forces
WindRC/Composite SeismicRC
SeismicComposite
Composite Building:
Veq1 = 3.81%*W = 24.9 MN
Veq2 = 4.05%*W = 26.5 MN
0
5
10
15
20
25
30
35
200000 800000 1800000 2800000 3800000
Overturning Moment
Seismic-Composite
Seismic-RC
Wind
RC/Composite
0
5
10
15
20
25
30
35
0 10 20 30
Storey
Inter-storey Drift
Seismic-RC
SeismicComposite
WindComposite
=h/(200.v.q)
=h/500
Wind-RC
Comparative Case Study of a Typical Tall Building in Singapore
Member Envelope Forces
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RC Building
Composite Building
Comparative Case Study of a Typical Tall Building in Singapore
Costing Assumptions:
Pricing information was collated & verified through a combination of local sources (based on 2013 prices)
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(, . )
() ($/3)
30 $ 155
0 $ 16050 $ 165
60 $ 170
($/) $ 1,500
($/) $ 6,000
($/2) $ 35
. ($/) $ 5,000
($/2)
1 B $ 40
($/2) $ 25
($/ / ) $ 0.60
Material Cost Information Courtesy of : Langdon & Seah
Bluescope Lysaght Hyundai E&C Yongnam
Comparative Case Study of a Typical Tall Building in Singapore
Building Weight (Normalized; including imposed loads)
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0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1.00
0.71
Comparative Case Study of a Typical Tall Building in Singapore
Concrete Costs (Normalized; excluding rebar & PT)
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0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.91.0
1.0
0.5
Comparative Case Study of a Typical Tall Building in Singapore
Rebar and Post-tensioning Costs (Normalized)
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98/110
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.0
0.3
&
Comparative Case Study of a Typical Tall Building in Singapore
Structural Steel Costs (Normalized; including Decking and FP)
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99/110
0.0
0.5
1.0
1.5
2.0
2.5
0.0
2.3
Comparative Case Study of a Typical Tall Building in Singapore
Foundation Costs (Normalized)
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100/110
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.0
0.7
Comparative Case Study of a Typical Tall Building in Singapore
Total Structural Material Costs (Normalized)
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0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.001.24
Comparative Case Study of a Typical Tall Building in Singapore
Total Structural Material Costs (Normalized)
7/24/2019 2 Design of Slender Tall Buildings for Wind and Earthquake.pdf
102/110
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.00
1.24 1.30
This cost premium is not unique. It will vary based on location, material rates, building type / form andstructural design parameters.
Comparative Case Study of a Typical Tall Building in Singapore
Total Project Construction Costs (Normalized)
7/24/2019 2 Design of Slender Tall Buildings for Wind and Earthquake.pdf
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0
0
1
1
1
1
1 1.03
The Big Picture ..
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Other Costs and Revenues
PROJECT COSTSGFA = 85,000 sq-m
The Big Picture ..
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GFA 85,000 sq mLand Cost = $19,000 per sq-m of GFALegal Fee & Stamp Duty = 4% of land costTotal Project Duration (including Design Period)= 33 months
Property Tax = 0.5% x land cost x duration)($)Associated Costs (Prof. & Site Supervision Fee) = ~ 8% of Total Construction CostMarketing & Advertisement = ~ 5% of Total Construction CostGST = 7% of Construction & Associated CostsInterest of Financing Cost for Land = 5% of Land Cost, Legal Fee & Property TaxInterest of Financing During Construction = 5% of Construction & Associated Costs x 0.5
RENTAL RETURN + PRELIMINARIESNet Efficiency= 80%Occupancy Rate= 80%Rental Rate $$/sq-ft/month= $12 per sq-ft per month
Preliminaries / month = 10% of Total Construction Cost
The Big Picture ..
Total Development Construction Costs (Normalized)
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0
0.2
0.4
0.6
0.8
1
1.2
1 1.005
Total Project Construction / Development Costs (Normalized)
The Big Picture ..
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1.03
0.9860.945
0.904
0.864
1.005
0.996 0.986 0.977 0.967
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
1.05
0 1 2 3 4
RC Building
Composite Adjusted TotalDevelopment Cost
Composite Adjusted TotalConstruction Cost
Savings in Construction Time (months)
Normaliz
edCots
Construction Time Saving (Months)
Norm
alizedCost
Besides productivity & costs what are theother intangible benefits of utilizing steel?
Composite Construction Benefits
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other intangible benefits of utilizing steel?
Higher quality
Lesser maintenance
More functional spaces
Flexibility to adaptation
Higher sustainability
Better performance under seismicactions
One Raffles Link
One Raffles Quay
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Concluding Remarks
Tall buildings present special challenges to
design & construction.
In Summary
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The challenges from wind and seismic loads canbe addressed through innovative designconcepts.
Composite buildings offer far higher potential forgreater productivity & hence lower costs.
Moving forward, more complex & taller buildingswill be conceived & constructed.
Structural engineers have the biggestcontribution to make in making buildings safe &economical.
How will these future tall buildings bedesigned & constructed?
The choice is yours