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An Evaluation of Current Site Response Analysis Methods

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.

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An Evaluation of Current Site Response Analysis Methods

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  1. 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

  2. The City Block Project

  3. Acknowledgments • National Science Foundation, CMMI 0830331 • Dr. AmjadAref, University at Buffalo • Ibrahim Almufti and Dr. Michael Willford, ARUP San Francisco • Dr. Boris Jeremic, UC Davis • Dr. Ben Mason, Oregon State University

  4. 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

  5. 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

  6. Outline • Introduction • Numerical Tools • Numerical Analysis • Sample Results • Conclusions and future research

  7. IntroductionSite Response Analysis • Purposes • Site effects for seismic hazard analysis • Soil-structure interaction analysis 1D site response analysis

  8. IntroductionSite 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)

  9. Numerical ToolsFrequency Domain • The equivalent linear approach: SHAKE and DEEPSOIL • Seed and Idriss (1969) • Iterative procedure • Modulus reduction and dampingcurves • Effective shear strain ratio • An empirical value of 0.65is recommended Hashash et al, 2010

  10. Numerical ToolsTime Domain • DEEPSOIL nonlinear • MKZ model (Matasovic, 1993) • Extended Masing rulesdefine the stress-strain hysteresis • Outcrop input using the Joyner and Chen (1975)method Hashash and Park (2001)

  11. 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

  12. Numerical Analyses Site Selection Site E1 Site W2 Site E2 Site W1 300m/s 2500m/s 1000m/s 100m 300m/s 2500m/s Bed Rock 2500m/s Bed Rock 2500m/s Bed Rock 1000m/s Bed Rock 1000m/s

  13. Numerical Analyses WUS Ordinary motions

  14. Numerical Analyses WUS Pulse motions

  15. Numerical Analyses CEUS motions

  16. Sample Results Site E1, Charlottsville

  17. Sample Results Site W1, Vasquez Park

  18. Sample Results Site W1, Rinaldi

  19. 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

  20. 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

  21. Contacts Chandu Bolisetti: cb76@buffalo.edu Dr. Andrew Whittaker: awhittak@buffalo.edu

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