Experimental Studies of Extracting Bridge Mode Shapes by Response of a Moving Vehicle

Abstract

Bridge inspections performed by the response of the moving vehicle have been widely studied because of its mobility and efficiency, whereas mode shapes extracted by the moving vehicle have low order and limited accuracy in existing studies. In this study, experimental studies are conducted in which a stationary shaker is used to excite the steady-state-forced vibration of the bridge, and the bridge vibration is collected by an accelerometer installed on a moving vehicle. Accurate multiorder mode shapes are obtained by extracting the vehicle acceleration envelope. First, a theoretical derivation of the method is provided, and an extraction process for field tests is proposed. Then, a model test of a three-span continuous beam bridge and a field test of a two-span continuous girder bridge are conducted. To verify the accuracy of the mode shapes extracted by the moving vehicle, reference data are obtained by finite-element modal analysis and by using the hammer test. Through a difference analysis of accelerations between the parked vehicle and the bridge deck under the test vehicle, the ability of the designed test vehicle to collect bridge vibration in different frequency bands is evaluated. Finally, the first five mode shapes of the bridge model and the first six mode shapes of the field bridge are extracted by a moving test vehicle, and the effects of vehicle speed and excitation amplitude on mode shape extraction are analyzed. The results show that multiorder mode shapes can be accurately extracted by a moving test vehicle.