SEISMIC PERFORMANCE OF STONE MASONRY AND UNREINFORCED CONCRETE RAILROAD BRIDGE PIERS

Railroads in the United States have numerous bridges that are at least 100 years old. With upgrading aged bridges, there is a push to reuse existing substructures while replacing entire superstructures. Often these substructures are unreinforced masonry (URM) or unreinforced concrete (URC). In order for the URM or URC elements to be incorporated into modernized bridges, they must be evaluated for their ability to withstand seismic loading. The U.S. railroad design code hypothesizes that the restraining effect of rail track reduces bridge damage during earthquakes. A structural modeling scheme for the ballast deck bridge and the open-deck girder bridge are proposed in SAP2000 using nonlinear link element to simulate the behavior of bearings and ballast structure under the lateral push. The experimental data from previous studies are used to calibrate and verify the proposed modelling scheme. The equivalent spring stiffness of the rail track system obtained by the modelling analysis is intended to be used in the subsequent small-scale shaking table experimental study which investigates the dynamic response of column shape rigid body specimens with spring restraint on top. Several parameters are considered in the test matrix such as stiffness of restraint spring, height/breadth ratio, ground excitations and single-body or multi-body configuration. The testing data prove the restraining effect of rail track applied on the top of the bridge piers. Coefficient of restitution is an important index to evaluate the kinetic energy loss during the impact for a rocking block. The models and expressions proposed by Housner and other researchers are reviewed comprehensively. A hypothetical model that includes three coordinates and consider the possible bouncing up scenario of the rigid block is proposed. A unified expression is developed in study