Two-axle test vehicle for bridges: Theory and applications

A closed-form solution is presented for the dynamic response of a two-axle asymmetric vehicle moving over bridges, along with potential applications highlighted. First, by modeling the vehicle as two concentrated loads moving over the bridge, closed-form solutions for the responses of the contact points are obtained. Second, by treating the vehicle as a two degree-of-freedom (DOF) system, closed-form solutions for the coupled vertical and rotational responses of the vehicle due to contact-point excitations are obtained. From vehicle's frequency response functions (FRFs), various phenomena are studied, including coupling, uncoupling, beat, resonance and cancellation. Resonance occurs when any excitation frequency coincides with any of the vehicle frequencies. No cancellation is observed when the two-DOF asymmetric vehicle degenerates into the uncoupled mode or a single-DOF vehicle. The results obtained are verified by an independent finite element analysis with virtually no assumptions. The advantage of using the two-axle asymmetric vehicle to scan the frequencies of the sustaining bridge is explored theoretically and numerically.