Fragility reduction for a simply supported multi-span prestressed rc bridge retrofitted with LRB

Current seismic hazard maps and code regulations impose a significant seismic demand to existing bridges, leading to the need of upgrading the seismic response of these structures and to mitigate the relevant seismic risk. One of the most adopted techniques to solve the problem in the field of bridge engineering is the use of isolation system that allow reducing the seismic actions on substructures by increasing the bridge fundamental period and by improving the dissipative capabilities of the structure. However, the use of this technique in case of simply supported decks usually requires the substitution of low thickness rubber pads with generally higher devices and the connection of simply supported spans through a kinematic chain. An alternative solution is the use of lead rubber bearings of low thickness, which does not require to modify the road altimetry, combined with nonlinear retaining systems located between the simply supported decks at supports, which prevent the pounding during the earthquake. The paper presents the fragility analysis of a bridge seismically retrofitted with this strategy in order to provide some insight into the effectiveness of the approach. The case study is a simply supported multi-span RC bridge located in Italy. A refined nonlinear finite element model of the bridge is developed, and results obtained from multiple-stripe analyses are presented in terms of fragility curves for the transverse response of the retrofitted bridge, focusing on its increasing in the seismic performance.