Seismic fragility assessment of Chilean skewed highway bridges

Abstract

The 2010 Maule, Chile earthquake demonstrated that many bridges were highly vulnerable to seismic demands. Among these bridges, skewed multi-span prestressed concrete girder bridges supported on non-anchored elastomeric bearings were the most vulnerable ones. After the 2010 Maule earthquake, several damaged skewed bridges were repaired and retrofitted using an updated seismic design criterion. Therefore, this study aims to compare the seismic performance of typical Chilean skewed highway bridges in their original design (prior to 2010) and in their repaired condition (post 2010). With this aim, three-dimensional (3D) nonlinear finite element models of four skewed bridges, which were damaged during the 2010 Maule earthquake, are developed and analyzed. Nonlinear static and incremental dynamic analyses (IDAs) are conducted, and fragility curves are obtained to evaluate the short-term evolution of the Chilean design practices. Additionally, the influence of the skew angle, vertical seismic bars, modelling assumptions and anchorage of elastomeric bearings, on the seismic performance of Chilean skewed highway bridges is analyzed through IDAs and fragility curves. The results of this study show that repair measures considered after the 2010 Maule earthquake improve the seismic performance of skewed bridges and effectively prevent span unseating. However, the adopted measures do not significantly improve the performance at slight to moderate damage states. It is also demonstrated that the skew angle and deck-abutment pounding have significant influence on the seismic performance. Finally, the results show that an adequate modelling of vertical elements, such as elastomeric bearings, must be considered to avoid underestimating displacement demands.