Seismic fragility of concrete bridges designed to current and older Aashto specifications

Bridges are essential components of transportation systems and their unacceptable performance following a disaster may lead to disruption to relief operations. Many existing bridges all around the world were designed based on early editions of seismic codes and the performance of some old bridges following seismic events has revealed that they are seismically vulnerable. This paper provides a comparison of the seismic performance of reinforced concrete (RC) bridges designed according to recent code editions and according to earlier provisions. To this end, a probabilistic seismic safety assessment of RC bridges was conducted. Non-linear response history analyses were performed for each set of bridge samples subjected to earthquake ground motions with different severities employing three-dimensional models. The effect of the earthquake focal mechanism on the seismic vulnerability of the bridges was investigated. Moreover, fragility curves were developed for RC bridges designed according to the latest edition of the American Association of State Highway and Transportation Officials (Aashto) specifications (so-called new bridges) and those designed based on pre-1980 specifications (so-called old bridges). The fragility curves are presented in terms of the geometrical specifications of the bridges and the focal mechanism associated with input motions for both new and old bridges.