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Probabilistic Seismic Performance of Rocking-Foundation and Hinging-Column Bridges

2011 UC Davis GGSS Roundtable April 8, 2011. Probabilistic Seismic Performance of Rocking-Foundation and Hinging-Column Bridges. Lijun Deng Advisors: Prof. Bruce Kutter , Prof. Sashi Kunnath University of California, Davis. Outline. Research motivation

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Probabilistic Seismic Performance of Rocking-Foundation and Hinging-Column Bridges

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  1. 2011 UC Davis GGSS Roundtable April 8, 2011 Probabilistic Seismic Performance of Rocking-Foundation and Hinging-Column Bridges Lijun Deng Advisors: Prof. Bruce Kutter, Prof. SashiKunnath University of California, Davis

  2. Outline • Research motivation • Development of computational model • Preliminary simulation results • Conclusions

  3. Research motivation Rocking-foundation system Hinging-column system vs. Plastic hinge Soil plastic hinge Conventional fixed-base foundation

  4. Case histories and experiment studies Hinging column: Kobe 1995 Rocking foundation: Kocaeli 1999 Hinging column: Centrifuge tests Rocking foundation: Centrifuge tests

  5. Outline • Research motivation • Development of computational model • Preliminary simulation results • Conclusions

  6. Computational model configuration

  7. Model parameters • Cy, Cr: base shear coefficients for column & rocking footing • Two yielding mechanisms: • Cr > Cy Hinging column system; • Cy > Cr Rocking foundation system Realistic values for highway bridges

  8. Model parameters • Input ground motions from PEER database Baker et al. (2010) • Concept of Incremental Dynamic Analysis (IDA)

  9. Outline • Research motivation • Development of computational models • Preliminary simulation results • Conclusions

  10. Selected animations • Cy=0.3, Cr=0.4, T=0.5 s (Hinging column) • Cy=0.4, Cr=0.3, T=0.5 s (Rocking foundation) Collapse case On-verge-of-collapse case On-verge-of-collapse case Collapse case

  11. Sa (T) vs. Max Deck Drift curves Sa (T) T

  12. Sa (T) vs. Max Deck Drift curves Rocking-footing system(Cy=0.4, Cr=0.3, T=0.5 s, Hc=10 m) Collapse 0.3 g Nonlinear Elastic Instability limit ~=3 m

  13. Probabilistic Analysis Rocking Footing (Cy=0.4, Cr=0.3, T=0.5 s, Hc=10 m) Note: Equivalent Static Analysis: a linear static pushover method

  14. Probabilistic Performance Comparison • Probabilistic performance of two systems are similar under less-intense motions, but rocking foundation is superior under intense motions.

  15. Sa (T) vs. Residual Deck Rotation • Bridge with rocking foundation have smaller rotation than hinging column  illustrates the recentering benefits

  16. Conclusions • Probabilistic performance of rocking-foundation and hinging-column bridge systems was evaluated using IDA methodology. • Rocking systems with Cr=0.3 produce less residual drift and similar max drift, and have lower probability of collapse in comparison with hinging column systems with Cy=0.3. • 3-m-tall system is easier to topple than 10- m-tall system. • The use of rocking foundation should be encouraged in seismic design of soil-foundation-structure systems.

  17. Acknowledgments • Caltrans (M. DeSalvatore, S. McBride, T. Shantz, and M. Khojasteh, contract 59A0575) • NSF-NEESR Project Soil and Structure Compatible Yielding to Improve System Performance • PEER project Last Hurdles for Rocking Foundations for Bridges • Student assistants: T. Algie (Auckland Univ., NZ), E. Erduran, J. Allmond (UCD), M. Hakhamaneshi (UCD). P E E R

  18. The end

  19. Validate model through centrifuge data Centrifuge model (Cy/Cr=5, T_sys=1 s, FSv=11.0)

  20. Input parameters in IDA model • Cy, Cr: base shear coefficients for column or rocking footing • Two yielding mechanisms: • Cr > Cy Hinging column system; • Cy > Cr  Rocking foundation system (Column hinge strength) (Foundation element stiffness) Equally spaced foundation elements (Column hinge stiffness) Ac/A=0.2, rm=0.2 (Footing length) (Foundation element strength)

  21. Fragility curves for two case studies

  22. Sa (T) vs. Max Deck Drift curves Hinging column (Cy=0.3, Cr=0.4, T=0.5 s, Hc=10 m) Rocking Footing (Cy=0.4, Cr=0.3, T=0.5 s, Hc=10 m) Collapse Collapse 0.3 g 0.3 g Nonlinear Nonlinear Elastic Elastic Instability limit ~=3 m Instability limit ~=3 m

  23. Collapse mechanisms • A hinge is a hinge • Hinges can be engineered at either position • A hinge forms at the edge when rocking occurs • P-delta is in favor for rocking – recentering • Instability limits are related to min{Cy, Cr} P P D D

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