OTREC-RR-11-08

Frequently traveled roads in Oregon are in seismically active areas. Many of our bridges were designed and built to lateral demands that were assumed to be less than the current expectation, due to improved awareness of seismic hazard and enhanced understanding of the non-linear response of bridges. This vulnerability to earthquakes can result in not only immediate damage, but also in the potentially lingering economic impact of disrupted traffic and freight. Fragility curves were constructed assuming lognormal capacity and demand distributions. Probability of failure was determined for slight, moderate, extensive, and complete damage. Statistical values were compared to the median and dispersion values proposed by other researchers, and calculated using guidelines from the HAZUS Technical Manual. Older multiple-span bridges were found to be significantly more fragile than the models. Through this modeling and analysis, the relative fragility of the modeled typical 3-span and 5-span bridges was determined.