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Transcript of Seismic Input and Soil- Structure Interaction (Ch. 5 of TBI report, PEER 2010/05) TBI Committee...
![Page 1: Seismic Input and Soil- Structure Interaction (Ch. 5 of TBI report, PEER 2010/05) TBI Committee Members Y. Bozorgnia C.B. Crouse J.P. Stewart October 8,](https://reader034.fdocuments.net/reader034/viewer/2022042821/56649cf75503460f949c79a5/html5/thumbnails/1.jpg)
Seismic Input and Soil-Structure Interaction
(Ch. 5 of TBI report, PEER 2010/05)
TBI Committee Members
Y. Bozorgnia C.B. CrouseJ.P. Stewart
October 8, 2010
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Outline
1. Seismic Hazard Analysis Probabilistic Deterministic Site-Response Analysis
2. Soil-Foundation-Structure Interaction Kinematic Inertial Input Motion Specification
3. Ground Motion Selection and Scaling Identification of Controlling Seismic Sources Ground Motion Selection Accelerogram Modification
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Two SHA Approaches
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Recommendation
Use General Procedure if geotechnical engineer is inexperienced or unqualified to perform site-specific probabilistic and deterministic SHA.
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Two SHA Approaches (cont.)
2. Site-Specific (Preferred) Probabilistic Deterministic
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Probabilistic Seismic Hazard Analysis (PSHA)
Source models Eqk locations M range Recurrence
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Probabilistic Seismic Hazard Analysis (PSHA)
Source models
Ground motion prediction equations (GMPEs):
mSa, sSa | (M, r, S, …)
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PSHA Output: Ground-Motion Hazard Curves
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Uniform Hazard Spectrum
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Recommendations for PSHA
For experienced PSHA users only
Use QA-checked software
Account for alternate seismic source parameters and GMPEs (epistemic uncertainty)
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Logic Tree
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GMPEs Recommended for Shallow Crustal Western U.S. Earthquakes
NGA GMPEs (2008) Abrahamson & Sliva Boore & Atkinson Campbell & Bozorgnia Chiou & Youngs Idriss
See EERI Spectra Journal (Feb. 2008, v. 24, no. 1)
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Empirical GMPEs Recommended for Subduction Earthquakes
Atkinson & Boore (2003) – Site Class B, C, D
Crouse (1991) – Soil Youngs et al. (1997) Soil and Rock Zhao et al. (2006) Soil Classes I – IV and
Hard Rock
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Deterministic MCE Calculation
Req’d per ASCE 7 Ch 21 Provides “cap” near major faults Arbitrary decisions regarding:
Ruptured fault segment (closest) Magnitude (use average of Mmax from logic
tree) Use same GMPEs & wts from PSHA Different sources may be most critical at
short and long periods
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Site-Specific Deterministic MethodASCE 7, Sect. 21.2.2
Find Fault à largest median Sa
Compute 1.5 x median Sa (ASCE 7-05)
Compute Sa84th >1.5Sa
median (ASCE 7-10)
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Site Response Analysis
ASCE 7-05; Ch.21Site-Specific Ground Motion
`
PSHA/DSHA – Vs30
PSHA/DSHA – Ref. Vs30
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Recommendations SRA not needed in absence of pronounced
impedance contrast (often the case for stiff soil sites)
Site effect can be accounted for in such cases through GMPE site terms
SRA advisable/required for:
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Recommendations SRA produces amplification factors, AF(T)=
Sa,soil/Sa,rock
Typically applied as deterministic modification of UHS (Hybrid proc.): Sa,soil=AF(Sa,rock)UHS
Can avoid with modification of site term in hazard integral (OpenSHA)
Unconservative bias
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2. Soil-Foundation-Structure Interaction (SFSI)
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SFSI for MCE
Linear springs and dashpots model soil-foundation interaction
Input motion same at all points along foundation
Input can be reduced for kinematic effects
See FEMA 440 & ASCE 41-06 for details
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3. Ground Motion Selection and Modification
Identify controlling earthquakes
Select representative ground motions
Modify accelerograms to match target spectrum
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Identify Controlling Earthquakes
Specify natural period band – SE decision Deaggregation Plots
T = 1 sec T = 5 sec
M1 – R1 M2 – R2
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Issues with Ground Motion Selection
Number of ground motion sets Multiple controlling earthquakes Near-fault effects Effects poorly represented in ground
motion database: Basin Effects M > ~ 8, long-duration motion
Use of simulations
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Number of Accelerograms - N
No less than three (use maximum responses)
Use average responses if 7 or more motions used
More needed if multiple controlling earthquakes
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Near Fault Effects
Select a(t) for both cases
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Transform FN & FP a(t) into X & Y a(t)
Fault
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Simulated Ground Motions (e.g., ShakeOut)
Sa (T = 3 sec, 5 = 5%)
gGraves et al. (2008)
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Simulated Ground Motions (e.g., ShakeOut)
Can produce realistic-appearing wave forms
Need for calibration
Most broadband methods are inadequately validated or have biases
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Issues with Ground Motion Modification
Target Sa
Site-specific Sa
Conditional mean Sa (CMS)
Modification procedures constant scaling spectral matching
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Target Sa
UHS encompasses many events Not achievable in a given event Scenerio spectra (CMS) more realistic; need > 1
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Accelerogram Modification
Constant Scaling
Spectral Matching
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Accelerogram Modification
Constant Scaling
Spectral Matching
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Spectral Matching
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Selection and Scaling Recommendations
N > 7 (N limited by $ and time) Use hazard deaggregations ® controlling EQs CMS – use several ® different Sa shapes Scaling (constant or spectral matching)
SE’s decision Simulated accelerograms (M > ~ 8)
- ADV: long duration and basin effects - DISADV: verification issues, access to quality simulations
Peer Review – Important