Probabilistic seismic performance assessment of an existing RC bridge with portal-frame piers designed for gravity loads only

The present analytical work illustrates a thorough assessment of the seismic performance of an existing reinforced concrete (RC) bridge with framed piers designed for gravity loads only. The seismic response is investigated through advanced, comprehensive and efficient dynamic non-linear analyses. The evaluation of the seismic performance for ductile and fragile components has been carried out with simplified yet reliable formulations, either based on codes or experimentally derived, partially validated with numerical simulations. The effects of far-field and near-source strong motions on the seismic response of the sample bridge have been assessed and discussed in details. Fragility curves are derived using both Cloud analysis and Incremental Dynamic Analysis (IDA) and considering two limit states, i.e. damage limitation and collapse. The outcomes of the refined numerical simulations show that the near-source strong motions tend to impose higher inelastic demand on fragile components of the bridge system than far-field records, nevertheless fragility curves relative to the latter records exhibit higher probability of failure than the near-source strong motion counterparts. For the damage assessment, it is found that the Cloud analysis lead to fragility curves similar to those derived through the IDA procedure. Finally, a new approach facilitating the preliminary identification of the weakest link of the bridge, namely the pier-by-pier fragility, is presented.