seismic performance assessment in dense urban environments
TRANSCRIPT
An Evaluation of Current Site Response Analysis Methods
Chandrakanth BolisettiGraduate Student Researcher
Dr. Andrew Whittaker Professor and Chair
Department of Civil, Structural and Environmental EngineeringUniversity at Buffalo, SUNY
The City Block Project
Acknowledgments
• National Science Foundation, CMMI 0830331
• Dr. Amjad Aref, University at Buffalo
• Ibrahim Almufti and Dr. Michael Willford, ARUP San Francisco
• Dr. Boris Jeremic, UC Davis
• Dr. Ben Mason, Oregon State University
Overview
• Soil-structure interaction analysis for performance assessment of buildings and nuclear power plants– Detailed 3D analyses– Nonlinear analyses for high intensity ground motions
• Evaluation of existing industry-standard numerical tools– Site response analysis (pre-requisite for SSI analysis)– SSI analysis
• SSSI analysis
Overview
• Soil-structure interaction analysis for performance assessment of buildings and nuclear power plants– Detailed 3D analyses– Nonlinear analyses for high intensity ground motions
• Evaluation of existing industry-standard numerical tools– Site response analysis (pre-requisite for SSI analysis)– SSI analysis
• SSSI analysis
Outline
• Introduction
• Numerical Tools
• Numerical Analysis
• Sample Results
• Conclusions and future research
• Purposes– Site effects for seismic hazard analysis– Soil-structure interaction analysis
Introduction Site Response Analysis
1D site response analysis
• State-of-the-art– Frequency domain equivalent linear analysis
• SHAKE, DEEPSOIL
– Time domain nonlinear analysis• DEEPSOIL nonlinear, LS-DYNA
– Mostly 1D• Limitations
– Mostly developed for characterizing site effects– The 1D assumption
• Horizontal ground motion components are usually not uncorrelated• Not sufficient for high fidelity SSI analyses required for performance
assessment of NPPs (Jeremic, 2011)
Introduction Site Response Analysis
Numerical Tools Frequency Domain
• The equivalent linear approach: SHAKE and DEEPSOIL– Seed and Idriss (1969)– Iterative procedure– Modulus reduction and damping
curves
• Effective shear strain ratio
– An empirical value of 0.65is recommended
Hashash et al, 2010
110MR
Numerical Tools Time Domain
• DEEPSOIL nonlinear– MKZ model (Matasovic, 1993)
– Extended Masing rulesdefine the stress-strain hysteresis
– Outcrop input using the Joyner and Chen (1975)method
0
1s
r
G
Hashash and Park (2001)
Numerical Tools Time Domain
• LS DYNA nonlinear– General finite element analysis
– Column of solid elementsconstrained to move in shear
– MAT_HYSTERETIC model (MAT_079)
– Outcrop input using the Joyner and Chen (1975) approach
– ARUP, San Francisco
Numerical Analyses Site Selection
Site E1 Site E2 Site W1 Site W2
2500m/s
300m/s
2500m/s
1000m/s 300m/s
Bed Rock2500m/s
Bed Rock2500m/s
Bed Rock1000m/s
Bed Rock1000m/s
100m
Numerical Analyses WUS Ordinary motions
0.01 0.1 1 100
0.2
0.4
0.6
0.8GM-1GM-2GM-3Site-W1Site-W2
WUS ordinary ground motions
Period (sec)
Acc
eler
atio
n (g
)
Event Station PGA (g)
Northridge, 1994 Vasquez Rocks Park 0.15
Northridge, 1994 Wonderland Ave 0.17
San Fernando, 1971 Lake Hughes #4 0.19
Numerical Analyses WUS Pulse motionsEvent Station PGA (g) Tp (sec)
Landers, 1992 Lucerne 0.73 5.1
Northridge, 1994 Rinaldi Receiving Stn. 0.83 1.5
Chi Chi, Taiwan, 1999 TCU 128 0.19 9.0
0.01 0.1 1 100
1
2
3LCN260 Tp = 5.12 secRRS228 Tp = 1.51 secTCU128 Tp = 9.00 secSite-W1Site-W2
Acceleration response spectra for selected pulse motions
Period (sec)
Acc
eler
atio
n (g
)
Numerical Analyses CEUS motionsEvent Station PGA (g)
Virginia, 2011 Charlottesville 0.10
New Hampshire, 1982 Franklin Falls Dam 0.31
Saguenay, CA, 1988 Dickey 0.09
0.01 0.1 1 100
0.25
0.5
0.75
1CVA090FFD315SNY090Site-E1Site-E2
CEUS ordinary ground motions
Period (sec)
Acc
eler
atio
n (g
)
Sample Results Site E1, Charlottsville
0.01 0.1 1 100
0.1
0.2
0.3
0.4ShakeMat HystereticDeepsoil
Comparison of acceleration response spectra at the surface
Period (sec)
Acc
eler
atio
n (g
)
0 0.025 0.05 0.075 0.1100
75
50
25
0ShakeMat HystereticDeepsoil
Peak acceleration profiles
Peak acceleration (g)
Dep
th b
elow
surfa
ce (m
)
0 1 10 4 2 10 4 3 10 4 4 10 4100
75
50
25
0ShakeMat HystereticRamberg OsgoodDeepsoil
Peak strain profiles
Peak strain (%)
Dep
th b
elow
surfa
ce (m
)
Sample Results Site W1, Vasquez Park
0.01 0.1 1 100
0.2
0.4
0.6
0.8ShakeMat HystereticDeepsoil
Comparison of acceleration response spectra at the surface
Period (sec)
Acc
eler
atio
n (g
)
0 0.05 0.1 0.15 0.2100
75
50
25
0ShakeMat HystereticDeepsoil
Peak acceleration profiles
Peak acceleration (g)
Dep
th b
elow
surfa
ce (m
)
0 0.01 0.02 0.03 0.04100
75
50
25
0ShakeMat HystereticDeepsoil
Peak strain profiles
Peak strain (%)
Dep
th b
elow
surfa
ce (m
)
Sample Results Site W1, Rinaldi
0.01 0.1 1 100
0.5
1
1.5
2ShakeMat HystereticDeepsoil
Comparison of acceleration response spectra at the surface
Period (sec)
Acc
eler
atio
n (g
)
0 0.375 0.75 1.125 1.5100
75
50
25
0ShakeMat HystereticDeepsoil
Peak acceleration profiles
Peak acceleration (g)
Dep
th b
elow
surfa
ce (m
)
0 0.5 1 1.5100
75
50
25
0ShakeMat HystereticDeepsoil
Peak strain profiles
Peak strain (%)
Dep
th b
elow
surfa
ce (m
)
Conclusions
• Good match for low soil strains but large differences at high soil strains (close to 1%)
• Peak strain values are underestimated in SHAKE, especially for intense motions– Effective shear strain ratio?
• Accelerations are underestimated in SHAKE– Large values of damping ratio?
• Implications for SSI analysis– Need to be cautious when large strains are expected– 1D analysis insufficient (Jeremic, 2011)– Materials not suitable for full SSI analyses
Conclusions
• High frequency ‘noise’ in time-domain analysis results– Piecewise nonlinearity (LS DYNA only)– Internal wave reflections due to impedance changes– Joyner and Chen (1974)– Cautious site layering, or filtering of the response
• SHAKE response for pulse motions– Convergence issues– Smaller value of effective shear strain ratio needs to be used
