Improved Fragility Functions for Bridges Susceptible to Large Ground Deformations and Liquefaction - 2572005

Project goals and objectives

The objective of this project is to improve fragility functions for bridges in liquefiable soil for assessing seismic risk of the San Francisco Bay Area transportation network. The need for improved fragility functions was identified through transportation network fragility analyses performed by Kiremidjian, which predicted that liquefaction would cause unrealistically widespread bridge damage and collapse. Liquefaction hazard was modeled using general guidelines inherent to the program HAZUS created by the Federal Emergency Management Agency, and the liquefaction hazard analysis was not specific to conditions in the Bay Area. A more careful region-specific consideration of liquefaction fragility is warranted since liquefaction was such a dominating factor in the transportation network analyses.

Topics that can be made more specific to the Bay area are:

1. Mapping of liquefaction triggering probability for a given level of ground shaking
2. Mapping of free-field ground displacement given liquefaction triggering
3. Estimating bridge damage state given a free-field ground displacement.

Each of these topics must specifically reflect conditions in the Bay area while remaining general enough to be implemented into the broad scope of the transportation network analysis program.

Role of this project in supporting PEER's mission (vision)

The improved fragility functions developed by this research will be utilized in a transportation network analysis that integrates all four aspects of the PEER PBEE framework (i.e. IM, EDP, DM and DV). It will demonstrate how improvements to a single component of the methodology can influence the global analysis results.

Methodology employed

This research consists of two primary tasks:

1. Utilize recent and ongoing efforts to map liquefaction in the Bay Area to develop probabilistic predictions of liquefaction triggering and ground displacement.
2. Perform suites of analyses in which ground displacements are imposed on bridge foundations to derive fragility functions relating bridge damage state to ground displacement. Uncertainty in the input parameters will be quantified and discrete event probabilities will be tracked for subsequent derivation of fragility functions.

Expected milestones & deliverables

Fragility functions for modeling the influence of liquefaction on bridges in the Bay Area designed to be used in conjunction with the analyses of the transportation network that have been performed using HAZUS (Kiremidjian PEER Project No. 3392003). Improved fragility functions will be provided 12 months following the start date for the project. A report detailing the work performed in this project will be provided to PEER at the end of the project period.