Identification of Frequencies and Damping Ratios of a Highway Overpass by Automatic Probing of Free Vibration Responses

The highway overpasses are a particular type of bridge because they are subjected to traffic loads and ground vibrations. Since the ground vibration induced by a vehicle passing on the road below the overpass usually performs like an impulse due to the short duration, the dynamic response of the overpass contains free vibration responses, which are more reliable for identification of the frequencies and damping ratios. Hence, this study introduces an approach to automatically probe the free vibration responses of an overpass and therefore identify its frequencies and damping ratios. First, the dynamic response of an overpass subjected to a vehicle passing on the road below the overpass is analytically analyzed to illustrate the occurrence of free vibration responses. Then, an algorithm is proposed to extract the free vibration responses based on the cross-correlation coefficient. Finally, the frequencies and damping ratios are obtained by decomposing the extracted attenuation responses using Prony’s method. Numerical simulations by constructing 3D FE models are conducted to verify the derived dynamic response of the overpass, validate the proposed frequency and damping ratio identification method, and investigate the effects of vehicle mass, vehicle speed, vehicle route, etc. on the identification performance. Field measurements on the Z24 bridge in Switzerland and the Guankou Middle Road overpass in Xiamen, China, are also employed to validate the proposed method, and the results show that the proposed method can automatically extract the free vibration responses and then identify the frequencies and damping ratios with high accuracy.