This paper focuses on the evaluation of the seismic vulnerability of pre-1990 highway concrete bridges, based on the development of analytical fragility curves. The parameters considered are the span length, column height, lap splices, reinforcement yield strength, and concrete compressive strength. Nonlinear response history analyses using 3D models were conducted for each set of bridge samples subjected to earthquake ground motions with different intensities. Moreover, this study analyzes the influence of the earthquake fault type on the seismic vulnerability of the bridges, using as a performance parameter the displacement ductility demand of the piers. Based on this parameter, to support future seismic-risk mitigation efforts fragility curves are utilized to assesses the seismic vulnerability of typical concrete bridge classes in Iran. The selected suite of seismic records originates in strike-slip and reverse fault seismic sources. The bridges subjected to reverse fault records present pier demands and seismic vulnerability larger than the bridges subjected to strike-slip accelerograms. The study shows that the span length, lap splice, column height, and seismic fault type have significant effects on the seismic vulnerability of bridge piers. Additionally, the results are useful to identify and prioritize retrofit actions of the most seismically vulnerable bridges.

Bridge damages during the past earthquakes caused several physical and economic impacts to transportation systems. Many of the existing bridges in earthquake prone areas are pre-1990 bridges and were designed with out of date regulation codes. The occurrences of strong motions in different parts of the world show every year the vulnerability of these structures. Nonlinear dynamic time history analyses were conducted to assess the seismic vulnerability of typical pre-1990 bridges. A family of existing concrete bridge representative of the most common bridges in the highway system in Iran is studied. The seismic demand consists in a set of far-field and near-field strong motions to evaluate the likelihood of exceeding the seismic capacity of the mentioned bridges. The peak ground accelerations (PGAs) were scaled and applied incrementally to the 3D models to evaluate the seismic performance of the bridges. The superstructure was assumed to remain elastic and the nonlinear behavior in piers was modeled by assigning plastic hinges in columns. In this study the displacement ductility and the PGA are selected as a seismic performance indicator and intensity measure, respectively. The results show that pre-1990 bridges subjected to near-fault ground motions reach minor and moderate damage states.