Project Summary

Liquefaction-induced lateral spreading has damaged bridges throughout the world during past earthquakes. Damage has been particularly intense in regions where a non-liquefiable crust material spreads laterally over underlying liquefied layers. The crust remains strong as it spreads, and is capable of exerting large demands on embedded bridge components. Recent research has clarified many of the loading mechanisms required to accurately predict the response of bridges in laterally spreading ground. However, many bridges were constructed decades ago when the hazard posed by liquefaction was not fully appreciated, and at a time before accurate engineering procedures had emerged for evaluating bridge response. The purpose of this research project is to develop fragility functions that characterize bridge damage as a function of free-field lateral spreading ground displacement. The fragility functions are intended to reasonably capture the stock of approximately 13,000 bridges owned by Caltrans. A companion study was conducted to estimate lateral spreading hazard at Caltrans bridge sites. Results from these research studies will be directly useful for screening the large bridge inventory to identify the most critical subset of bridges for more systematic evaluation and possible retrofit.

The fragility functions are being generated using numerical simulations using the finite element software platform OpenSees. The input parameters are varied to reasonably capture the range of soil conditions ans structural configurations characteristic of Caltrans bridge stock. Engineering demand parameters such as curvature ductility in the piers, pile cap displacement, and abutment displacement are related to free-field ground displacement. Disaggregation of the input parameters identifies particular combinations of soil and structural conditions that are most susceptible to liquefaction- induced lateral spreading.


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