Seismic analysis of soil-pile-bridge-train interaction for isolated monorail and railway bridges under coupled lateral-vertical ground motions

Abstract

Most of the common monorail bridges in the world are non-isolated ones due to their low superstructure weight. Recently, a limited study on the innovative isolated monorail bridges demonstrated that seismic isolation systems can be beneficial to monorail bridges. In this study, a parametric analysis of soil-pile-bridge-train (SPBT) interaction during frequent earthquakes was performed to better understand the seismic behavior of the novel isolated monorail bridges compared to the traditional non-isolated monorail bridges and the conventional railway bridges. To evaluate the influence of train-bridge interaction (TBI) on the seismic response of bridges under the combined vertical and horizontal ground motions, Taiwan Railway Bridge (TRB), and Qom Monorail Bridge (QMB) with and without isolators were selected. A total of 2268 time history analyses, including different isolator shear modulus, train locations in two vehicle modeling approaches, pier heights, and ground motions in different directions, were performed using the substructuring method. The results were verified by comparing the 3D continuum finite elements. The observations indicated that when lateral and vertical excitations were applied simultaneously, for monorail bridges where the trains’ weight usually reached up to 50% of the weight of a couple of the guideway beams, the presence of the train led to creating the critical conditions. However, for the conventional railway bridges with relatively low train-to-deck weight ratios (less than 30%) ignoring the train could cause the most critical responses in the SPBT system, regardless of the vehicle modeling approach. It was also found that the efficiency of seismic isolation systems for conventional railway bridges is higher than that for monorail bridges.