case study #2: peer/ssc tall building design
TRANSCRIPT
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Tony Ghodsi
Case study #2
PEER/SSC Tall Building Design
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Acknowledgments:
Jose Antonio Flores Ruiz Robert Englekirk
Claire Massie Yangbo Chen Erzen Hoda Maria Bravo
Kathy Lee
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Location:
• Downtown Los Angeles, CA.
Story heights:
• 10.5 ft. typical
• 13.6 ft. from ground floor to 2nd
• 11.5 ft. at roof
Use:
• 42 Story Hotel / residential with 4 parking levels below ground
Building Description
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Slab Construction:
• 10 in. thick at parking
• 12 in. thick at ground floor
• 8 in. thick post-tensioned typical
• 10 in. thick at roof
Seismic Weight:
• 102,000 kips (Above ground floor)
Building Description
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Building 2
Building 2A Building 2B
Code design
IBC 2006
ASCE 7-05 ACI 318-08
LATBSDC 2008
Service Level Collapse Prevention
25 years return period
2,475 years return period
Design Program
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Stiffness Modifiers
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Stiffness Modifiers
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Stiffness Modifiers
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Typical Plan View at Ground Floor and Below
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Typical Plan View at 2nd Floor and Above
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Code Design Building 2A
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Building 2A Shear Wall properties Shear wall thickness and
concrete strength
t = 18”
f’c = 5,000 psi
t = 24”
f’c = 6,000 psi
20th
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Frame Beam Properties
30” x 36”
f’c = 5000 psi
Frame column concrete strength
f’c = 6,000 psi
f’c = 5,000 psi
15th
10th
Ground
f’c = 8,000 psi
f’c = 10,000 psi
Frames A & F
Interior & Corner columns
36” x 36”
Building 2A Frame Properties
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Frame column concrete strength
f’c = 5,000 psi
f’c = 6,000 psi
15th
10th
Ground
f’c = 8,000 psi
f’c = 10,000 psi
Frames 2 & 5
Interior columns at gridline B & E
42” x 42” from Ground to 25th
36” x 36” from 25th to Roof
Interior columns at gridline C.5
46” x 46” from Ground to 10th
42” x 42” from 10th to 25th
36” x 36” from 25th to Roof
Building 2A Frame Properties
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VB = 0.043 W
Design base shear:
T1 = 5.50 sec.
T2 = 4.97 sec.
T3 = 2.98 sec.
Periods: Site specific design response spectra
Building 2A Periods and Base Shear
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Vb min = 0.043 W
Period = 5.5 sec
Vb site specific = 0.112 W
Design Ductility
R = 2.6
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Building 2A Static Shear Distribution
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Maximum inter-story drift allowed
0.020 hn
Building 2A Inter-story Drifts
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Service Level and Collapse Prevention Design Building 2B
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1. Service level check is for an earthquake event of 25 year return period with 2.5% viscous damping.
3. Up to 20% of the elements with ductile actions are allowed to reach 150% of their capacity under the serviceability check.
5. The minimum base shear specified by the LATBSDC (2008) is waived.
7. Strengths for ductile actions at service level are calculated using strength reduction factors per ACI 318-08.
Exceptions from LATBSDC
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Performance Design
t = 16”
f’c = 5,000 psi
t = 24”
f’c = 8,000 psi
20th
30th
t = 18”
f’c = 6,000 psi
t = 18”
f’c = 5,000 psi
t = 24”
f’c = 6,000 psi
20th
Code Design Shear Wall Concrete Strength and Thickness Comparison
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Corner Column Concrete Strength and Size Comparison Performance Design Code Design
f’c = 6,000 psi
f’c = 5,000 psi
15th
10th
Ground
f’c = 8,000 psi
f’c = 10,000 psi
36” x 36” f’c = 6,000 psi
f’c = 5,000 psi
22nd
18th
3rd
f’c = 8,000 psi
f’c = 10,000 psi
36” x 36”
42” x 42”
30th
10th
46” x 46”
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Response Spectrum Analysis for Service Level Earthquake Building 2B
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• Gravity load combinations per IBC 2006
• Earthquake actions at service level per
DL + 0.25LL ± Eservice
Service Level Acceptance Criteria
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T1 = 4.13 sec.
T2 = 3.81 sec.
T3 = 2.21 sec.
Periods:
VBx = 0.043 W
VBy = 0.047 W
Base Shear:
2.5% damped service level site specific response spectra
Building 2B Service Level Periods and Base Shear
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Ductile actions:
Expected material properties
φ per code
Brittle actions:
Specified material properties
φ per code
CAUTION:
Specified material properties
φ per code
Could result in the same design as that prescribed
by code
Strength of Elements at Service Level
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Classification of Actions
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Overall drift allowed at service level
0.005 hn
Inter-story Drifts at Service Level
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Modal Analysis Peak Shear at Service Level on X Direction
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Pier 1 Service Level Peak Shear on X Direction
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150% φVNexpected
20% of elements
Coupling Beam Shear Demand at Service Level
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Frames 2 & 5 Beam Moment Demand at Service Level
Positive Moments Negative Moments Positive Moments Negative Moments
Corner Beam-Column Joint Interior Beam-Column Joint
20% of elements
150% φΜNexpected
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Step by Step Time-History Non-Linear Analyses at MCE Level Building 2B
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Collapse Prevention MCE Level Acceptance Criteria
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Collapse Prevention MCE Level Acceptance Criteria
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Collapse Prevention MCE Level Acceptance Criteria
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Collapse Prevention MCE Level Acceptance Criteria
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Collapse Prevention MCE Level Acceptance Criteria
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Ductile actions:
Average of 7 records
Brittle actions:
Average of 7 records times 1.5
Expected material properties
φ of 1
Demand Actions at MCE Level
Expected material properties
φ equals 1
Element Capacity at MCE Level
Specified material properties
φ equals 1
Element Properties for Non-Linear Model
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T1 = 4.93 sec.
T2 = 4.50 sec.
T3 = 2.78 sec.
Periods:
Base Shear:
VBx = 0.154 W
VBy = 0.190 W
MCE target response spectra
Building 2B MCE Periods and Average Base Shear
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MCE Records Adjusted to Match Target Response Spectra
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Peak Story Shear at MCE Level
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Maximum inter-story drift allowed at MCE
level
0.030 hn
Inter-story Drifts at MCE Level on X direction
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Pier 1 MCE Average Shear on X Direction
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Maximum compression strain allowed for confined concrete
εu = 0.015 in/in
Maximum compression strain allowed for unconfined concrete
εu = 0.003 in/in
Compression Strain at Corner by Pier 1
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Maximum Coupling Beam rotation allowed
θu = 0.06 rad
Coupling Beam Rotation at MCE Level
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Corner Column Peak Shear on X Direction at MCE Level
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0.4 f’cexp Ag
Corner Column Peak Compression at MCE Level
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θu = 0.045 rad
Frame A Peak Beam Rotation at MCE Level
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T1 = 5.5 sec.
T2 = 4.97 sec.
T3 = 2.98 sec.
Code design periods
Base Shear:
VBx = 0.043 W
VBy = 0.043 W
T1 = 4.13 sec.
T2 = 3.81 sec.
T3 = 2.21 sec.
VBx = 0.043 W
VBy = 0.047 W
T1 = 4.93 sec.
T2 = 4.50 sec.
T3 = 2.78 sec.
VBx = 0.154 W
VBy = 0.190 W
Service level periods MCE level periods
Period and Base Shear Comparison
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Landers Yermo maximum shear on X direction
VBx = 11.1 % VBx = 13.5 %
20 % increase
Lateral Restrain Provided by Soil Below Ground Floor
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VBx = 10.7 % VBx = 15.4 %
44 % increase
Loma Prieta Gilroy maximum shear on X direction Lateral Restrain Provided by Soil Below Ground Floor
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Compression
178% increase
Code design column at seismic base:
36”x 36” column
f’c = 8,000 psi
Non-linear design column at seismic base:
46”x 46” column
f’c = 10,000 psi
Corner Column Axial Load Comparison
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φPn /
(f’c
Ag)
φPn,max = 0.8φ [0.85f ’c(Ag-Ast) + fyAst] Eq. 10-2 ACI 318-08
Code Maximum Axial Load
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4#9 T&B
4#9 T&B
29th
8#9 T&B
Code design: Performance design:
Frame Beam Longitudinal Reinforcing Comparison
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Code design: Performance design:
4#9
6#10
21st
14th 4#11
4#10
10#11
21st
10th
8#11
6#10
32nd
Coupling Beam Diagonal Reinforcing Comparison
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MCE Pseudo-velocity Response Spectra Comparison At 1 second:
Code = 57 in/sec
Site Specific PEER = 47 in/sec
Downtown 1 & 2 70 in/sec
Westwood = 84 in/sec
At 5 seconds:
Code = 57 in/sec
Site Specific PEER = 43 in/sec
Downtown 2 = 50 in/sec
Westwood = 61 in/sec
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The Englekirk Companies Questions?