CONTENTS - Regional...

CONTENTS The keys of the presentation

1) Project Information

2) Analysis and Design Approaches

3) CTBUH Seismic Design Guidelines 4) Conclusions

2.1) Structural system & construction methodology 2.2) Construction sequence & Wished-in-Place models

© Council on Tall Buildings

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1. Project Information MahaNakhon Tower


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MahaNakhon Tower Future highest building in Bangkok

314m


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77 Storeys: 76 superstructure levels 1 basement.

314 m Height + 5 m basement: Tallest building in Thailand.

Quantities:

Concrete works: 94 000 m3 Raft: 21400 m3. Superstructure: 72 600 m3.

Steel Rebars: 14 000T. Raft: 3200T. Superstructure: 10 800T.

Post-Tension: 381 T for 50700m² of PT slabs.

Sky bar

Sky Residences

Residences

Hotel

Retail & Car Parking © Council on Tall Buildings

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Structural Conceptual Design: - ARUP Beijing Structural Design Development (D&B) Construction Stage: - Warnes Associates - ARUP Australia - Bouygues-Thai - Bouygues Batiment International Structural Design Peer Review: - Robert Bird (Australia). - Aurecon Project management: - Archetype


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2. Analysis and Design Structural Design of the tower


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2.1 Structural system & Construction methodology

1) Mat Foundation

2) Core walls

3) Columns

4) Outriggers

5) Floor slabs © Council on Tall Buildings

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8.75m/4.5m Thick

21,400 m3 of concrete

12 concrete pours, over a period of 2 months

3,200 T of steel rebars

129 Barrettes 1.20m x 3.00m Tip level at -65m.

Mat Foundation


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22m x 22m from the B1 to L20.

22m x 17m from the L21 to L52.

22m x 14m from the L52 to Top.

Core walls


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12 Mega-columns around the core

Concrete strength 60 MPa

Columns


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Outriggers 3 LEVELS OF OUTRIGGERS (TECHNICAL LEVELS) :

L51-L52 L35-L36 L19-L20

REINFORCED CONCRETE DEEP WALLS; Double floor Height (8.0m)


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OUTRIGGER

CORE

WAL

L

COLU

MN

COLU

MN

Increase stability under lateral Loads

Outriggers


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Outrigger connecting time

Connection at early stage Connection at late stage

Constructability Normal Complicate

Tower lateral stability (at construction stage)

Normal Less

Outrigger internal forces Higher forces Lower forces

Differential Axial shortening between the core wall and the columns

Less problem More problem

CONNECT THE OUTRIGGER AT THE TIME WE REACH THE OUTRIGGER FLOOR “OR” AFTER?


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Post-Tension band beams 600mm thick.

8m cantilever slab in the corners

Slabs


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EXAMPLE OF SKY RESIDENCE FLOOR

Columns in the corners for the Residential Floors

Post-Tension Band beams 800mm/600mm and 450mm thick.

Slabs


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Stage Analysis Model

Full Model in one go = “Wished-In-Place Model”

Impact of the stage analysis model = Increase in column loads. Reduction in core gravity loads. > better prediction of core wall shortening Reduction in design actions in outriggers.

2.2 Construction Sequence & Wish-in-Place FE models


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Ultimate Models Ultimate Lateral Model on Flexible foundation - Short term material and foundation stiffness. - modified to reflect degree of cracking

Ultimate Gravity Model on Flexible foundation - Long term material and foundation stiffness. - modified to reflect degree of cracking.

Ultimate Lateral Model on Rigid foundation - Short term material stiffness. - modified to reflect degree of cracking

Ultimate Gravity Model on Rigid foundation - Long term material stiffness. - Modified to reflect degree of cracking.

Models - Summarize


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Service Model For drift and acceleration determination Short term material and foundation stiffness. - Modified to reflect degree of cracking in service. - Dynamic for acceleration: E28 x 1.05 + rebar.

Service Models Models - Summarize


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Models - Summarize

Model details and naming system

Flexible foundation Rigid foundation Construction sequence FE

gravity system models

Model naming "CS" (C-construction sequence, S-spring support)

Long term spring supports Stage 1: Raft foundation only

Stage 2: Raft to L19 Stage 3: Raft to L35 Stage 4: Raft to L51

Stage 5: Raft to Roof

Model naming "CF" (C-construction sequence, F-Fixed support)

Fixed supports Stage 1: Fixed support to L19 Stage 2: Fixed support to L35 Stage 3: Fixed support to L51

Stage 4: Fixed support to Roof

Wish-in-Place FE lateral system

models

Model naming "US 475" (U-ultimate lateral forces, S-spring support, short term)

Model naming "US 2475" (U-ultimate lateral forces, S-spring support, short term)

Model naming "UF 475" (U-ultimate lateral forces, F-

fixed support)

Model naming "UF 2475" (U-ultimate lateral forces, F-

fixed support)


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3. CTBUH Seismic Design Guidelines Recommendations for the Seismic Design of High-rise Buliding


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Codes, Standards, Guidelines and Recommendations

IBC 2006/ ASCE 07-05/DPT1302-52 Seismic Design ACI 318-99 Building Code Requirements for RC design and detailing

AISC 2005 & AWS Design and detailing of structural steel members and joints

ISO137 or ISO-6897 Vibration and human comfort

DPT 1311 Performance of the tower under wind load.

CEB-FIB 90 or equivalent (AS3600)

Relative shortening of vertical components and compensation.

CTBUH 2008 Recommendations for the seismic design of High-rise building: (Appendix B)

for performance check

Codes, Standards and Guidelines Combination of Gravity, Seismic and Wind loads


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Thai Local Code - 475 year return period

CTBUH Appendix B – 2475 year return period

Seismic Approach

Design Seismic Load

Performance base design check

“For buildings sited in regions of low seismic hazard, a collapse-level assessment using nonlinear response history analysis need not be performed if all of the following items are satisfied”


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CTBUH Recommendations for the Seismic Design of High-rise Buildings – Appendix B for Regions of Low Seismic Hazard

1) The seismic hazard is based on the mean 2475-year maximum direction spectrum

2) Damping ratio in any mode associated with the first 90% of the reactive mass is no greater than 2%. Accidental torsion need not be considered in the analysis.

3) The strength capacity associated with deformation-controlled actions is based on expected values, and the strength capacity associated with force controlled actions is based on specified values.

M & T

V & C © Council on Tall B

uildings

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5) Component strengths for the check of item 4 are computed considering the most adverse co-existing actions computed by analysis of the framing system

6) Structural components in the building with strength demand-to-capacity ratios greater than 1.0 are designed and detailed as components of an intermediate framing system per ASCE-7-05 and all material standards referenced therein unless calculations based upon first principles engineering mechanics are prepared by the designer to show that less onerous details are required to

4) The ratio of strength demand-to-capacity for load combinations involving 2475-year earthquake effects is less than 2.0 for all deformation- and force controlled actions


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7) Structural components in the building with strength demand-to-capacity ratios less than 1.0 do not require earthquake related construction details (e.g., closely spaced transverse reinforcement).

8) Foundations are designed and detailed for the lesser of a) elastic demands associated with the spectrum of item 1, and b) the maximum overturning moment and base shear that the

structural framing can deliver to the foundation, accounting for all possible sources of reserve strength. © Council on Tall B

uildings

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Seismic Approach

Seismic parameter comparison

Parameters Thai local seismic code/ IBC, ASCE 7-05

CTBUH Seismic Design Guidelines, Appendix B

Analysis method

Modal analysis

Response spectrum

Site Specific Hazard Assestment

Seismic return period

475 Years 2475 Years

Damping ratio 5% 2% Response

modification factor, R

4 1

Seismic Mass DL+SDL+0.25LL Demand to

Capacity ratio 1 2

Phi(Ø, Strength reduction

factor)

0.7 to 0.9 1 © Council on Tall B

uildings

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Seismic Approach

The approach for the intermediate detailing of the different element types adopted for MahaNakhon Tower

Structural element Intermediate detailing requirements for elements with a demand to capacity ratio greater than 1 and less than 2

Beams, columns and coupling beams Detail in accordance with clause 21.3 of ACI318-99 as an intermediate moment frame.

Outriggers Limit the demand to capacity ratio to less than 1 to ensure an elastic response.

Base of Core wall If the concrete compressive strain is more 0.3% then use special shear wall detailing (i.e. boundary elements). This is only required at the base of the wall (minimum one storey).

If the concrete compressive strain is less than or equal to 0.3% then use ordinary shear wall detailing.


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Seismic Approach

Due to the limited time frame for the design and built process, a non-linear time history analysis was impractical. Though the actual comparison of the performance assessment from this approach cannot be achieved, forces from these two approaches are presented here as a rough comparison.

In order to compare the design forces, a factor of ½ is multiplied to the forces from CTBUH approach due to the fact that the allowable demand to capacity ratio is 2.0, while a factor of 1/Phi is multiplied to the forces from local code.


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Comparison of Seismic Story Shear

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70

Stor

y

STORY SHEAR (MN)

VX UF 475

VX US 475

VY UF 475

VY US 475

VX UF 2475

VX US 2475

VY UF 2475

VY US 2475

CT

BU

H

times

(1/2

)

x

y

Tha

i loc

al c

ode

times

(1/P

hi)


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Comparison of Seismic Story Moment

0

10

20

30

40

50

60

70

80

0 1000 2000 3000 4000 5000 6000 7000

STO

RY

SEISMIC STORY MOMENT (MN-m)

Mx UF 475

Mx US 475

My UF 475

MY US 475

Mx UF 2475

Mx US 2475

MY UF 2475

MY US 2475

x y

CT

BU

H

times

(1/2

) T

hai l

ocal

cod

e tim

es (1

/Phi

)


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Comparison of Seismic Column Axial Forces

0

10

20

30

40

50

60

70

80

0 2000 4000 6000 8000 10000 12000 14000

Stor

y

SEISMIC COLUMN AXIAL FORCE (kN)

C2 EX UF 475

C4 EX UF 475

C8 EX UF 475

C10 EX UF 475

C2 EX 2475

C4 EX 2475

C8 EX 2475

C10 EX 2475

C2

C4

C10

C8

CT

BU

H

times

(1/2

) T

hai l

ocal

cod

e tim

es (1

/Phi

)


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Comparison of Seismic Story Drift

0

10

20

30

40

50

60

70

80

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Stor

y

DRIFT (%)

Drift EX UF 475

Drift EX US 475

Drift EX UF 2475

Drift EX US 2475


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Comparison of Seismic Story Shear and Ultimate Wind Story Shear

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70

Stor

y

STORY SHEAR (MN)

VX UF 475

VX US 475

VY UF 475

VY US 475

VX UF 2475

VX US 2475

VY UF 2475

VY US 2475

Wind X 90 C2

Wind Y 90 C2

Wind X 0 C2

Wind Y 0 C2

CT

BU

H

times

(1/2

) tim

es

(Phi

) T

hai c

ode


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4.3 Element design – Columns and Core walls

475yr 2475yr


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4. Conclusions


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4. Conclusions

1) MahaNakhon Tower was designed taking into consideration the actual construction sequences using bounded support conditions: fixed supports and long-term/short-term spring supports to ensure that the structural main elements such as mega columns, outriggers, core walls and raft foundation can resist the possible load distribution.

2) CTBUH seismic design guidelines require stronger response spectrum accelerations and more elastic properties in the structural elements in terms of a lower damping ratio without any response modification factor. However, CTBUH allows the demand-to-capacity ratio to be as high as 2.0 without any capacity reduction phi, Ø. © Council on Tall B

uildings

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4. Conclusions

3) Since the seismic loads govern only in some portions of the building, then the higher demands from CTBUH can be taken cared to ensure the structural performance. This CTBUH approach is economically appropriate for the high-end luxury tower like MahaNakhon

4) Appendix B of the CTBUH seismic guidelines mostly gives recommendations on strength issues and detailing requirements which are more about ductility; especially when the demand to capacity ratio is greater than 1.0. No deformation/drift limit is specified. © Council on Tall B

uildings

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THANK YOU FOR YOUR ATTENTION


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