Application of Laser Measurement to the Drive-by Inspection of Bridges

This paper introduces the application of laser vibrometer measurements to the drive-by inspection of bridges. Drive-by methods usually process the acceleration response measured from an accelerometer installed on a vehicle passing over a bridge. In this paper, two laser vibrometers and two accelerometers are installed on the vehicle to measure a rela-tive velocity between the bridge and vehicle and the vehicle acceleration. The vehicle velocity is removed from the relative velocity by subtracting the time integration of the vehicle accel-eration. It is shown by subtracting two following bridge spatial velocities at moving coordi-nates, that the spatial velocity of the road roughness can be removed. As a result, the bridge velocity at the moving coordinate is obtained. By applying the FFT to the bridge velocity, the fundamental frequency of the bridge is visible in the spectrum.