An Evaluation of Current Site Response Analysis Methods Chandrakanth Bolisetti Graduate Student Researcher Dr. Andrew Whittaker Professor and Chair Department of Civil, Structural and Environmental Engineering University 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 Introduction Site Response Analysis 1D site response analysis • Purposes – Site effects for seismic hazard analysis – Soil-structure interaction analysis Introduction 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) 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 R M 1 10 – An empirical value of 0.65 is recommended Hashash et al, 2010 Numerical Tools Time Domain • DEEPSOIL nonlinear – MKZ model (Matasovic, 1993) G0 1 r s – Extended Masing rules define the stress-strain hysteresis – Outcrop input using the Joyner and Chen (1975) method Hashash and Park (2001) Numerical Tools • LS DYNA nonlinear – General finite element analysis – Column of solid elements constrained to move in shear – MAT_HYSTERETIC model (MAT_079) – Outcrop input using the Joyner and Chen (1975) approach – ARUP, San Francisco Time Domain Numerical Analyses Site E1 Site E2 Site Selection Site W1 Site W2 300m/s 2500m/s 1000m/s 300m/s 2500m/s Bed Rock 2500m/s Bed Rock 2500m/s Bed Rock 1000m/s Bed Rock 1000m/s 100m Numerical Analyses WUS Ordinary motions 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 WUS ordinary ground motions 0.8 GM-1 GM-2 GM-3 Site-W1 Site-W2 Acceleration (g) 0.6 0.4 0.2 0 0.01 0.1 1 P eriod (sec) 10 Numerical Analyses WUS Pulse motions Event 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 Acceleration resp onse sp ectra for selected pulse motions 3 Acceleration (g) LCN260 T p = 5.12 sec RRS228 T p = 1.51 sec T CU128 T p = 9.00 sec Site-W1 Site-W2 2 1 0 0.01 0.1 1 P eriod (sec) 10 Numerical Analyses CEUS motions Event Station PGA (g) Virginia, 2011 Charlottesville 0.10 New Hampshire, 1982 Franklin Falls Dam 0.31 Saguenay, CA, 1988 Dickey 0.09 CEUS ordinary ground mot ions 1 CVA090 FFD315 SNY090 Site-E1 Site-E2 Acceleration (g) 0.75 0.5 0.25 0 0.01 0.1 1 P eriod (sec) 10 Sample Results Site E1, Charlottsville Peak acceleration profiles Comparison of acceleration response spectra at the surface Peak strain profiles 0 0 0.4 Shake Shake Mat Hyst eretic Deepsoil Shake Mat Hysteretic Mat Hyst eretic Ramberg Osgood Deepsoil Deepsoil 0.3 25 50 Depth below surface (m) Acceleration (g) Depth below surface ( m) 25 0.2 50 0.1 75 75 0 0.01 0.1 1 10 P eriod (sec) 100 100 0 0 0.025 0.05 0.075 110 4 4 210 0.1 P eak strain (%) P eak acceleration (g) 4 310 410 4 Sample Results Site W1, Vasquez Park Peak acceleration profiles Peak strain profiles 0 0 Shake Mat Hyst eretic 0.8 Deepsoil Shake Mat Hyst eretic Deepsoil Comparison of acceleration response spectra at the surface Shake Mat Hyst eretic Deepsoil 25 25 50 Depth below surface ( m) Acceleration (g) Depth below surface ( m) 0.6 0.4 75 50 75 0.2 100 0 0.05 0 0.01 0.1 P eak acceleration (g) 0.15 100 0.2 0.1 0 0.01 1 P eriod (sec) 0.02 P eak strain (%) 0.03 0.04 10 Sample Results Site W1, Rinaldi Peak acceleration profiles Peak strain profiles 0 0 Shake Mat Hyst eretic Deepsoil2 Shake Mat Hysteretic Deepsoil Comparison of acceleration response spectra at the surface Shake Mat Hyst eretic Deepsoil 25 25 50 Depth below surface ( m) Acceleration (g) Depth below surface ( m) 1.5 1 75 50 75 0.5 100 0 0.375 0 0.01 0.75 P eak acceleration (g) 1.125 100 1.5 0.1 0 0.5 1 P eriod (sec) 1 P eak strain (%) 1.5 10 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 Contacts Chandu Bolisetti: cb76@buffalo.edu Dr. Andrew Whittaker: awhittak@buffalo.edu