1 / 25

Incremental Dynamic Analyses on Bridges on various Shallow Foundations

Incremental Dynamic Analyses on Bridges on various Shallow Foundations. Lijun Deng PI’s: Bruce Kutter , Sashi Kunnath University of California, Davis. NEES & PEER annual meeting San Francisco October 9, 2010. Outline. Introduction and centrifuge model tests

mitch
Download Presentation

Incremental Dynamic Analyses on Bridges on various Shallow Foundations

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Incremental Dynamic Analyses on Bridges on various Shallow Foundations Lijun Deng PI’s: Bruce Kutter, SashiKunnath University of California, Davis NEES & PEER annual meeting San Francisco October 9, 2010

  2. Outline • Introduction and centrifuge model tests • Incremental Dynamic Analysis (IDA) model • Preliminary results of IDA • Maximum drift • Instability limits of rocking and hinging systems • Residual drift • Conclusions

  3. Damaged columns in past earthquakes

  4. Centrifuge test matrix

  5. Rocking Foundation Centrifuge Tests Gazli earthquake, pga= 0.88 g

  6. Hinging Column Centrifuge Test Gazli earthquake, pga= 0.88 g

  7. Photos of hinging column after 0.88g Gazli shake

  8. Hinging Column Centrifuge Test CHY024, pga=0.23 g

  9. Collapse of hinging column • SDOF bridges on rocking foundation survived after 20 scaled GM’s, but the one on fixed foundation and hinging column collapsed

  10. OpenSeesmodel for IDA and parametric study Mass = m Column hinge spring Column: Stiff elasticBeamColumn Kθ Hc Foundation: zerolength elements Moment Fixed ground center Rotation Footing center Footing mass = m*rm ki xi Lf

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

  12. 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)

  13. Input parameters in IDA model • Input ground motions from PEER database Forty pulse-like ground motions at soil sites(Baker et al. 2010)

  14. IDA results: Sa(T=T_sys) vs. max drift Rocking Footing (Cy=0.5, Cr=0.2, T_sys=0.85 s) Hinging column (Cy=0.2, Cr=0.5, T_sys=0.85 s) 0.2 g Failure zone 0.2 g Failure zone Nonlinear zone Nonlinear zone Elastic zone Elastic zone Instability limit ~=2 m Instability limit ~=2.2 m

  15. 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 your favor for rocking – recentering • Instability limits are related to Cy and Cr values P P D D

  16. Selected animations • Cy=0.2, Cr=0.5, T=0.85 s (Hinging column) • Cy=0.5, Cr=0.2, T=0.85 s (Rocking foundation) Collapse case On-verge-of-collapse case On-verge-of-collapse case Collapse case

  17. IDA results: Sa(T=T_sys) vs. max drift • 50% median of Sa vs. max drift and +/-σ 50% Median

  18. Compare medians of Sa vs. max drift for various T_sys • Longer periods lead to higher drift • The max drift is not sensitive to Cy/Cr ratio • The max might rely on min{Cy, Cr}, to be confirmed with further study

  19. IDA results: Sa (T_sys) vs. Residual Rotation 50% Median

  20. IDA results: Sa (T_sys) vs. Residual rotation • Bridge with rocking foundation have smaller rotation than hinging column  re-confirm the recentering benefits

  21. Conclusions • Rocking foundations provide recentering effect that limits the accumulation of P-D demand (i.e., much smaller residual rotation) • Experiments and IDA simulations show column with rocking footing is more stable than hinging column (i.e., fewer collapse cases) • ESA approach is not conservative for highly nonlinear cases • Analysis is ongoing, and fragility functions are being developed from the results. We are also evaluating the adequacy of Sa(T_sys) as an Intensity Measure of ground motions

  22. Collaborators CONSTRUCTION DESIGN THEORY Khojasteh Shantz GEOTECHNICAL Kutter Martin Mejia Desalvatore Stewart Jeremic CODE DEVELOPERS Hutchinson Panagiotou Browning Kunnath Comartin Mahin Moore McBride Ashheim Mar Mahan BRIDGES STRUCTURAL BOTH BUILDINGS

  23. Acknowledgments • Current financial support of California Department of Transportation (Caltrans). • Network for Earthquake Engineering Simulation (NEES) for using the Centrifuge of UC Davis. • Other student assistants: T. Algie (Auckland Univ., NZ), E. Erduran (USU), J. Allmond (UCD), M. Hakhamaneshi (UCD).

  24. The end

  25. IDA results: Sa(T=T_sys) vs. max drift Rocking Footing (Cy=0.5, Cr=0.2, T_sys=0.85 s) Hinging column (Cy=0.2, Cr=0.5, T_sys=0.85 s) • Equivalent Static Analysis (ESA) commonly used in codes may underestimate the displacement.

More Related