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) 2

3. What is SSI? – Inertial Effects 3

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

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 9

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

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

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

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

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

15. Foundation Impedances Longitudinal 15 Transverse

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

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

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

19. Large Amplitude Shaking in Longitudinal Direction 19

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

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

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

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

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

25. Thank You