Heavy vehicles are often present on bridges during earthquakes, potentially affecting the seismic response of the structure. This study investigates the seismic behavior of a single span, two lane steel-concrete composite I-girder bridge subjected to vehicular loads specified by the Indian Roads Congress (IRC) in combination with seismic excitations. A finite-element model is developed using MIDAS Civil and validated in accordance with IRC provisions. Response spectrum analyses are conducted for Indian seismic Zones IV and V, along with linear time history analyses using recorded ground motions from the Bhuj (2001), Chamoli (1999), and India–Burma Border (1995) earthquakes. Stationary vehicular loads, including IRC Class A, Class AA, Class 70R, and Special Vehicle configurations, are applied at mid-span to obtain critical structural responses. The results indicate that stationary vehicles increase shear force, bending moment, and mid-span deflection, with heavier axle loads and closer axle spacing producing greater amplification. Seismic demands in Zone V are approximately 50% higher than those in Zone IV. Time history analyses show that the near-field Chamoli record generates responses up to three times greater than those from the Bhuj and India–Burma Border events. Overall, the findings demonstrate a non-linear relationship between axle load and seismic response, highlighting that both load magnitude and axle configuration significantly influence the dynamic demand.
