Using vehicle–bridge contact spectra and residue to scan bridge's modal properties with vehicle frequencies and road roughness eliminated

Abstract

Both vehicle frequencies and road roughness are factors that may render the vehicle scanning method ineffective for bridges. In this paper, both factors will be eliminated via the skillful use of a two-axle test vehicle. Namely, the effect of vehicle frequencies is removed by using the vehicle–bridge contact (point) responses and road roughness by the residue of the front and rear contact responses of the two-axle test vehicle. Firstly, the contact responses for the two axles are derived from the vertical and rotational equations of motion for the test vehicle. Next, the contact response is processed by the variational mode decomposition (VMD) to yield the component response and then by the Hilbert transform (HT) to yield the mode shape. The parametric study has demonstrated that (1) more bridge frequencies can be extracted from the contact responses presented due to removal of vehicle frequencies; (2) the VMD-HT technique for recovering mode shapes is robust with regard to vehicle damping and speed; (3) the proposed procedure in its entity is good not only for single-span but for multi-span bridges; and (4) the residue of the axles' responses can effectively reduce road roughness in identifying bridge modal properties.