Upload
buinhu
View
230
Download
2
Embed Size (px)
Citation preview
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, 2010
Outline
1. Seismic Hazard Analysis Probabilistic Deterministic Site-Response Analysis
2. Soil-Foundation-Structure Interaction Kinematic Inertial Input Motion Specification
5. Ground Motion Selection and Scaling Identification of Controlling Seismic Sources Ground Motion Selection Accelerogram Modification
Two SHA Approaches
Recommendation
Use General Procedure if geotechnical engineer is inexperienced or unqualified to perform site-specific probabilistic and deterministic SHA.
Two SHA Approaches (cont.)
2. Site-Specific (Preferred) Probabilistic Deterministic
Probabilistic Seismic Hazard Analysis (PSHA)
Source models Eqk locations M range Recurrence
Probabilistic Seismic Hazard Analysis (PSHA)
Source models
Ground motion prediction equations (GMPEs):
µSa, σSa | (M, r, S, …)
Probabilistic Seismic Hazard Analysis (PSHA)
Source models Ground motion prediction equations
(GMPEs)
Log Accel.
P depends on no. of standard deviations A is above/below am am
a
PSHA Output: Ground-Motion Hazard Curves
Uniform Hazard Spectrum
Deaggregation Plot for L.A.
Recommendations for PSHA
For experienced PSHA users only
Use QA-checked software
Account for alternate seismic source parameters and GMPEs (epistemic uncertainty)
Logic Tree
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)
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
Ratio of 1.0 s SA 2007 and 2002 National Seismic Hazard Maps for WUS 2% Probability in 50 Years
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
1992 Landers, CA M 7.3 Earthquake
Sommerville et al. (1997)
Lucerne Record, 1992 Landers Earthquake
Sommerville et al. (1997)
Fault Normal (FN) Fault Parallel (FP)
Lucerne Response Spectra
Sommerville et al. (1997)
FN
FP
Deterministic SHA
Required per Ch 21 of ASCE 7 Usually governs MCE for sites near
active faults Recommendations
Use same GMPEs, weights and parameter values used in PSHA
Maximum Magnitude May want use higher Mmax than weighted average
Mmax from logic tree
Site-Specific Deterministic Method ASCE 7, Sect. 21.2.2
Find Fault largest median Sa
Compute 1.5 x median Sa (ASCE 7-05)
Compute Sa84th >1.5Sa
median (ASCE 7-10)
Fault Map
Median Deterministic Response Spectra H Comp.
0
0.5
1
0 0.5 1 1.5 2 2.5 3 3.5 4
T (sec)
Elysian Park Thrust Newport Inglewood San Andreas
S a
M 7.8 San Andreas Earthquake Simulations
Graves et al. (2008)
Site Response Analysis ASCE 7-05; Ch.21
Site-Specific Ground Motion
`
PSHA/DSHA – Vs30
PSHA/DSHA – Ref. Vs30
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:
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
(may not be necessary)
Site Class F
SRA (cont.)
input motion
SRA (cont.)
input motion
Building Input Motion
Seismic Wavelengths
2. Soil-Foundation-Structure Interaction (SFSI)
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
Basement Wall – Soil Interaction
flexible wall
pt. x
floor
Wall Reponses at Pt. x
Pt. x
3. Ground Motion Selection and Modification
Identify controlling earthquakes
Select representative ground motions
Modify accelerograms to match target spectrum
Identify Controlling Earthquakes
Specify natural period band – SE decision Deaggregation Plots
T = 1 sec T = 5 sec
M1 – R1 M2 – R2
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
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
Near Fault Effects
Select a(t) for both cases
Transform FN & FP a(t) into X & Y a(t)
Fault
Simulated Ground Motions (e.g., ShakeOut) Sa (T = 3 sec, 5 = 5%)
g Graves et al. (2008)
Simulated Ground Motions (e.g., ShakeOut)
Can produce realistic-appearing wave forms
Need for calibration
Most broadband methods are inadequately validated or have biases
Basin Effects
Amplify long period motions Increase duration
Issues with Ground Motion Modification
Target Sa Site-specific Sa
Conditional mean Sa (CMS)
Modification procedures constant scaling spectral matching
Target Sa
UHS encompasses many events Not achievable in a given event Scenerio spectra (CMS) more realistic; need > 1
CMS – e Parameter
M > ~ 8, Long Duration Motion
San Andreas fault M ~ 8
Cascadia and S. Alaska subduction zone M 9+
Velocity Records for M 7.8 San Andreas Event
Graves et al. (2008)
km
Accelerogram Modification
Constant Scaling
Spectral Matching
Accelerogram Modification
Constant Scaling
Spectral Matching
Constant Scaling Method
0
1
2
3
0 1 2 3 4 5 T (sec)
EQ-IV x 1.3 1940 Imperial Valley, El Centro (2.00) 1971 San Fernando, 8244 Orion Blvd. (1.74) 1979 Imperial Valley, El Centro Diff Array (1.74) 1989 Loma Prieta, Saratoga Aloha Ave. (1.88) 1992 Landers, Yermo Fire Station (2.00) 1994 Northridge, Sylmar Hospital (1.10) 1999 Duzce, Turkey, Duzce Station (1.36)
Sa (g)
Spectral Matching
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