Probabilistic seismic performance of rocking foundation and hinging column bridges
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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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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. SashiKunnath

University of California, Davis


Outline

Outline

  • Research motivation

  • Development of computational model

  • Preliminary simulation results

  • Conclusions


Research motivation

Research motivation

Rocking-foundation system

Hinging-column system

vs.

Plastic hinge

Soil plastic hinge

Conventional fixed-base foundation


Case histories and experiment studies

Case histories and experiment studies

Hinging column:

Kobe 1995

Rocking foundation:

Kocaeli 1999

Hinging column: Centrifuge tests

Rocking foundation: Centrifuge tests


Outline1

Outline

  • Research motivation

  • Development of computational model

  • Preliminary simulation results

  • Conclusions


Probabilistic seismic performance of rocking foundation and hinging column bridges

  • Computational model configuration


Model parameters

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


Model parameters1

Model parameters

  • Input ground motions from PEER database

Baker et al. (2010)

  • Concept of Incremental Dynamic Analysis (IDA)


Outline2

Outline

  • Research motivation

  • Development of computational models

  • Preliminary simulation results

  • Conclusions


Selected animations

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


Sa t vs max deck drift curves

Sa (T) vs. Max Deck Drift curves

Sa (T)

T


Sa t vs max deck drift curves1

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


Probabilistic analysis

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


Probabilistic performance comparison

Probabilistic Performance Comparison

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


Sa t vs residual deck rotation

Sa (T) vs. Residual Deck Rotation

  • Bridge with rocking foundation have smaller rotation than hinging column  illustrates the recentering benefits


Conclusions

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.


Acknowledgments

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


Probabilistic seismic performance of rocking foundation and hinging column bridges

The end


Validate model through centrifuge data

Validate model through centrifuge data

Centrifuge model

(Cy/Cr=5, T_sys=1 s, FSv=11.0)


Input parameters in ida model

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)


Fragility curves for two case studies

Fragility curves for two case studies


Sa t vs max deck drift curves2

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


Collapse mechanisms

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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