abstract
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 farfield 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.
7. Conclusions
The seismic assessment of an existing Italian RC bridge with portal-frame piers, designed for gravity loads only has been presented. A simple yet efficient methodology for the sample bridge is proposed as well. Such procedure is versatile and sound for the implementation in codes of practice. Two structural limit states were defined: the damage limit state (DLS) and the collapse limit state (CLS). The analysis scheme encompasses reliable capacity formulations for the transversal section of the structural elements. Therefore, adequate formulations for the evaluation of the structural capacity of the structural elements of the portal frames of the piers have been considered. A new definition for brittle DLS capacities is proposed, based on the CLS formulation.
The seismic response of the sample bridge structure has been investigated through dynamic non-linear analyses. Moreover, fragilities have been derived through comprehensive and efficient procedures, such as Cloud and IDA. Two sets of 30 strong motion records have been used to study the effects of far-field and nearsource strong motions. Moreover, for sake of completeness, an additional set of 60 strong motions obtained combining the two previous sets, has been adopted.
It was observed that the brittle failure of the transverse beams of piers governs the bridge response. Additionally, the comprehensive numerical investigations carried out in the present work show that, on average, the near-source strong motions tend to impose higher and more variable inelastic demand on fragile components of the bridge system than far-field records. Nevertheless, the fragility curves relative to the latter records exhibit higher probability of failure than the near-source strong motion counterparts. Such results comply with recent observations presented in the literature.
