Full-Response Prediction of Coupled Long-Span Bridges and Traffic Systems under Spatially Varying Seismic Excitations

A long-span bridge supports a large number of vehicles, which are usually present when an earthquake strikes the bridge site due to the low predictability of earthquake events. Existing seismic analyses of long-span bridges have failed to characterize the comprehensive coupling effects among the bridge structure, vehicles, and spatially varying seismic excitations. A new full-response prediction methodology for the coupled bridge–traffic interaction system under spatially varying earthquake excitations was developed by capturing the interaction effects not only between the bridge and moving vehicles, but also between the earthquake excitations and the coupled bridge–traffic system. Different from most existing bridge seismic analyses, in which only traditional earthquake loads in terms of inertial forces are applied on the bridge structure, the new formulation also incorporated the coupled earthquake forces on both the bridge and vehicles, which were expressed as functions of the bridge–traffic coupling matrices and earthquake displacement inputs. The proposed methodology was numerically demonstrated on a prototype long-span bridge and traffic system under spatially varying earthquake excitations. The full responses of the bridge and vehicles were predicted when the bridge–traffic system was subjected to earthquake excitations. Numerical results suggest that the coupled earthquake force as derived in the present study has notable influence on the dynamic performance of the bridge and vehicles under seismic excitations.