Mode shape construction for bridges from contact responses of a two-axle test vehicle by wavelet transform

Wavelet transform (WT) is theoretically studied to recover the bridge mode shapes from a passing two-axle test vehicle by using the correlation between the front and rear contact points. In this paper, closed-form solution is derived for the dynamic response of the bridge. To avoid the masking effect brought by vehicle’s natural frequencies on bridge’s natural frequencies, the wheel-bridge contact responses are used instead, which are derived from the vehicle responses considering the suspension effect. Next, the WT is employed to obtain the ridges of the bridge component response, based on which the bridge mode shapes are retrieved by using the correlation between the front and rear contact points. Conclusions made for this study include: (1) the contact responses for the two-axle test vehicle can be better used for frequency extraction than the vehicle responses; (2) the WT can be successfully used for constructing bridge mode shapes; (3) the procedures proposed for calculating the contact responses and for recovering the bridge mode shapes are robust with regard to the vehicle damping and speed for beam-type bridges; and (4) the mode shapes recovered by the proposed procedure are good even in the presence of pavement roughness with the aid of ongoing traffic.