Seismic vulnerability assessment and fragility curves for a multistorey gallery arch bridge

The masonry bridges on the Kalka Shimla Mountain Railway line, which have multiple arch galleries in the form of Roman aqueducts, are spectacular. The Kalka Shimla Mountain Railway line is situated in severe seismic zones (Indian Standard 1893:2016). This research assesses the seismic vulnerability of masonry arch Bridge No. 541 situated on the Kalka Shimla Mountain Railway line. This bridge is the tallest on the route. In particular, it assesses the seismic vulnerability of the bridge using finite element (FE) analysis. For this purpose, an FE model for the bridge is developed using the ABAQUS FE-based environment. The experimental field study conducted on the bridge using an ambient vibration test (AVT) and dynamic parameters (frequency and mode shapes) is evaluated by operational modal analysis (OMA). Further, the FE model is updated by modifying the elastic mechanical property of the stone masonry to match the analytical modal frequency with the results of the AVT and OMA. The updated model is then used to perform a pushover analysis and nonlinear dynamic analysis to estimate the seismic performance of the bridge. Furthermore, fragility curves are developed for the bridge to estimate the damage state for specific seismicity. The study shows that the bridge is vulnerable to Zone IV seismicity and needs some retrofitting in specific locations such as the pier–abutment joints.