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
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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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and Urban Habitat
© Council on Tall Buildings
and Urban Habitat
© Council on Tall Buildings
and Urban Habitat
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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© Council on Tall Buildings
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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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© Council on Tall Buildings
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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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© Council on Tall Buildings
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© Council on Tall Buildings
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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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© Council on Tall Buildings
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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
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CTBUH Recommendations for the Seismic Design of High-rise Buildings – Appendix B for Regions of Low Seismic Hazard
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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CTBUH Recommendations for the Seismic Design of High-rise Buildings – Appendix B for Regions of Low Seismic Hazard
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
and Urban Habitat
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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and Urban Habitat
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
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THANK YOU FOR YOUR ATTENTION
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