Dynamics of multi-span continuous straight bridges subject to multi-degrees of freedom moving vehicle excitation

The paper presents an analytical approach to the problem of vehicle–bridge dynamic interaction. Starting from early studies based on a simply supported beam interacting with a lumped mass moving at constant speed, in recent years researchers have improved the models of both the bridge and the vehicle. On this basis, the bridge is modelled here as a multi-span continuous isotropic plate; its response to external loads is defined by applying the mode superposition principle and takes into account both flexural and torsional mode shapes, the latter being usually neglected in the literature. The plate is considered proportionally damped and its modes are computed by means of the Rayleigh–Ritz method. The scheme adopted for the vehicle consists of a seven degrees-of-freedom system moving at constant speed over the isotropic rough bridge surface. The numerical investigation, based on these analytical models, refers to a three-span bridge and includes the importance of torsional mode shapes, of road surface irregularities and of vehicle speed.