Prioritization of Bridges for Seismic Retrofitting

This report presents a prioritization method developed for seismic retrofitting of bridges. The method is used to identify bridges that are in most need of retrofitting and rank order these bridges based on the vulnerability and importance criteria.

Vulnerability assessment includes evaluation of the seismic hazard at the bridge site, classification of existing bridges into bridge classes and fragility analysis. Vulnerability is expressed as a function of seismicity in order to capture the direct effect of ground motion on damage. New bridge classes are defined based on the proposition that bridges with similar structural characteristics will experience similar damage under a given seismic loading. An expert system is developed to classify bridges into bridge classes. The need for the development of fragility curves for each bridge class is emphasized.

Importance assessment considers the attributes that relate the consequences of failure of a bridge to the public safety and socio-economic well-being of a community. The importance of a bridge is conceived to be closely related to its function within the transportation network system. Network analysis is used to evaluate the emergency response factor that assesses the impact of disruption of the available routes or the time delays due to destroyed components after an earthquake. A value model is developed to properly determine the multi-attribute importance criterion that depends on the decision maker and his or her objectives. The developed value model is also used to integrate the vulnerability and importance criteria.

A detailed review and critique of the existing prioritization methodologies is included. The developed methodology is illustrated by an example application conducted for the Palo Alto, California area.