Identification of bridge bearing disengagement by instantaneous frequencies extracted from the acceleration of a passing heavy vehicle

Bridge bearing disengagement is often observed from the continuous girder bridge, which has the largest number of bridges. This study proposes an indirect method to identify the bridge girder-bearing separation using the time-varying instantaneous frequency extracted from the dynamic response of a heavy vehicle passing over a continuous girder bridge. Firstly, the dynamic response of a dual-axle heavy vehicle passing over a two-span continuous girder bridge is derived, where the time-varying instantaneous frequency is incorporated by the frequency modulation technique. Then, the iterative variational nonlinear chirp mode decomposition (i-VNCMD) is proposed to extract the time-varying instantaneous frequency from the dynamic response of the passing heavy vehicle. When the heavy vehicle passes over the bridge without bearing disengagement, the instantaneous frequency curve shows a periodic pattern due to the bearings; however, when the heavy vehicle passes over the bridge with bearing disengagement, the periodic pattern is broken, and the instantaneous frequency when the vehicle is just passing over the separated bearing drops significantly. Numerical simulations validate the proposed method and investigate the effects of vehicle mass, vehicle speed, number of bridge spans, and road surface roughness, etc. on the proposed method. An experimental study on a three-span continuous bridge in the laboratory is also presented to validate the proposed method further.