Weak-End and Frequency Detection of Elastically Supported Bridges by Contact Residual Response of Two-Axle Test Vehicle in a Round Trip

The two support bearings of an elastically supported (ES) bridge may be unequal in stiffness due to aging or other factors. This paper proposed an effective technique of using the contact residual response (CRR) generated by a two-axle test vehicle in its round-trip movement to detect the weak end and frequencies of the bridge. First, the round-trip CRR is presented in closed form. It is featured by three facts: (1) the CRR is given in terms of the vehicle-bridge "contact" response and thus is free of the annoying vehicle's frequency; (2) being created as the "residual" of the responses of the two axles, the CRR is immune to the disturbance of the surface roughness; and (3) by letting the vehicle move in "round trip," the weak end of the bridge can be detected, while all the bridge frequencies are enhanced. A procedure is presented for calculating the CRR considering the discrete nature of field measured data recorded by the test vehicle. In the numerical study, the closed-form solution is validated using the finite-element method (FEM). The results from a realistic example demonstrated that weak-end amplification can be clearly recognized for the CRR (both temporal and spectral) for the vehicle moving in a round trip. Such a feature enables the weak end of the bridge to be easily detected. The other advantage is that more bridge frequencies of higher orders can be identified using the CRR generated by the vehicle moving from the weak end.