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Foundation Flexibility and Damping from Forced Vibration Testing of Field Structure

Foundation Flexibility and Damping from Forced Vibration Testing of Field Structure. Lisa M. Star Michael J. Givens George Mylonakis Jonathan P. Stewart 7-11-2012. What is Soil-Structure Interaction (SSI)?.

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Foundation Flexibility and Damping from Forced Vibration Testing of Field Structure

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  1. Foundation Flexibility and Damping from Forced Vibration Testing of Field Structure Lisa M. Star Michael J. Givens George Mylonakis Jonathan P. Stewart 7-11-2012

  2. What is Soil-Structure Interaction (SSI)? SSI is the collection of effects that soil behavior has on a structure and structural behavior has on the soil Two Important SSI effects: • Altered Ground Motions (Kinematic Interaction Effects) • Foundation Stiffness and Damping (Inertial Interaction Effects)

  3. What is SSI? – Inertial Effects

  4. What is SSI? – Inertial Effects

  5. What is SSI? – Inertial Effects

  6. What is SSI? – Inertial Effects

  7. What is SSI? – Inertial Effects

  8. The SSI Problem • Foundation flexibility changes structure behavior and the failure mode • Conservative or unconservative? from ATC 40

  9. UCLA SSI Test Structure • 2.13 m x 4.26 m foundation • 2.13 m tall HSS 12”x12”x1/2” steel columns • 0.25 m thick reinforced concrete upper deck • Removable bracing

  10. Field Test Sites - WLA NEES@UCSB Wildlife Refuge Liquefaction Field Site

  11. Field Test Sites - GVDA NEES@UCSB Garner Valley Field Site Test structure-soil-structure interaction

  12. Foundation Stiffness and Damping Adapted from Tileylioglu et al. (2011)

  13. Existing SSI Models • Function of G, , and foundation dimensions Baseline Knowledge Report, Stewart et al. 2010

  14. Foundation Impedance - Theory Translation and Rotation: Adapted from Tileylioglu et al. (2011)

  15. Foundation Impedances Longitudinal Transverse

  16. WL - Foundation Impedance - Shaking in Longitudinal Direction Compared to Pais and Kausel (1988) Model 1: Vs=108 m/s Model 2: Vs=98 m/s Max Strain: 0.00045% G/Gmax: >0.985

  17. WL - Foundation Impedance - Shaking in Transverse Direction Compared to Pais and Kausel (1988)

  18. GVDA - Foundation Impedance - Shaking in Transverse Direction Compared to Pais and Kausel (1988) Model 3: Vs=207 m/s

  19. Large Amplitude Shaking in Longitudinal Direction

  20. Large Amplitude - Shaking in Longitudinal Direction Compared to Pais and Kausel (1988)

  21. Large Amplitude - Shaking in Longitudinal Direction Compared to Pais and Kausel (1988)

  22. Large Amplitude - Shaking in Transverse Direction Compared to Pais and Kausel (1988)

  23. Summary and Conclusions • There were a very small number of field scale tests available. The experiment provides high quality data that is freely available to other researchers. • Soil-Foundation Impedances: • We find that kx weakly decreases with f and kyy strongly decreases with f • We find that  is strongly dependant on f • Nonlinear Soil-Foundation Impedance: • Foundation stiffness decreases as strain increases • Damping increases as strain increases

  24. Acknowledgements • NEES@UCLA • NEES@UCSB • NEES@Utexas • SalihTileylioglu, Ph.D. • NSF CMMI 0618804, PI Jack Moehle • NSF CMMI 0927178 (NEES Operations, PI Julio Ramirez)

  25. Thank You

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