2 design of slender tall buildings for wind and earthquake.pdf

7/24/2019 2 Design of Slender Tall Buildings for Wind and Earthquake.pdf

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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)


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)


T(sec)


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)


T(sec)


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



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L7


Si T D b i


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L10



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L36A

g ,


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L46


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L50


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L56



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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


,

=

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


0

50

100

150

200

250

0 500000 1000000

Impact of Seismic Loads


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,

=

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)


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)



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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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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%


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


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


Member Envelope Forces


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RC Building

Composite Building


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


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


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


Rebar and Post-tensioning Costs (Normalized)


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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

&


Structural Steel Costs (Normalized; including Decking and FP)


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0.0

0.5

1.0

1.5

2.0

2.5

0.0

2.3


Foundation Costs (Normalized)


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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


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


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

1.00

1.24 1.30

This cost premium is not unique. It will vary based on location, material rates, building type / form andstructural design parameters.


Total Project Construction Costs (Normalized)


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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

2 design of slender tall buildings for wind and earthquake.pdf

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