Vehicle Scanning Method for Bridges

4Vehicle Scanning of Bridge Frequencies: Experiment

Following the theoretical development in the preceding two chapters, a single‐axle, two‐wheel cart towed by a light truck is used to scan the frequencies of vibration of the sustaining bridge, as a feasibility test of the idea presented. The truck excites the bridge through its movement at a constant speed, thereby serving as an exciter to the bridge. The vibration of the bridge is transmitted via the contact point and scanned by an accelerometer mounted inside the test cart. The bridge that is set into motion by the truck will dominate the vertical dynamic response of the test cart in movement, which, in turn, serves as a scanner or message receiver of the vertical oscillation or dynamic properties, i.e., frequencies, of the sustaining bridge. The response recorded by the accelerometer mounted on the test cart during its passage over the bridge is then processed by the fast Fourier transform (FFT) to extract the frequencies of excitation or vibration transmitted from the bridge. The feasibility in scanning the fundamental frequency of the bridge using the moving test cart is confirmed by the field tests conducted in a highway bridge located in northern Taiwan. The methodology developed for the first time herein is simple and efficient, and can be promisingly applied to scanning a wide range of bridge structures, if only the fundamental frequency is of interest. The materials presented in this chapter are based primarily on ...