Numerical Analysis of Seismic Vulnerability and Dynamic Response of Underground Interchange Structures Under Traveling Wave Effects

The underground interchange structure is a crucial component of urban underground construction facilities. Its seismic performance in soft ground under the influence of traveling-wave effects has not yet been studied. If not addressed in a timely manner, it will pose serious construction safety risks. This study develops a two-dimensional finite element model of a representative underground interchange, employing the multi-linear kinematic–dynamic interaction model to capture nonlinear material behavior. Incremental dynamic analysis is integrated with probabilistic fragility assessment to examine damage evolution, deformation, internal forces, and stress responses under both uniform and non-uniform seismic inputs. Results indicate that the overall seismic performance is satisfactory, with a low probability of exceeding moderate damage. Plastic damage is concentrated in the central frame and the base of the right-hand wall. Compared with traveling-wave excitations, uniform inputs generally produce larger displacements, particularly in the lower structure. Although axial and shear forces show limited sensitivity to wave type or propagation velocity, they increase significantly under non-uniform input, with axial forces reaching up to 16.9 times those under uniform excitation. Non-uniform input also doubles stress extremes and intensifies stress concentrations at frame nodes. These findings underscore the need to incorporate traveling-wave effects into seismic evaluation and offer methodological insights for the design and reinforcement of underground interchanges in weak soils.