Estimating Bridge Fundamental Frequency from Vibration Response of Instrumented Passing Vehicle: Analytical and Experimental Study

Driving velocity, natural frequency of vehicle and natural frequency of bridge are the main contributing factors to vibration of a vehicle when passing a bridge. By separating contributions of the first two factors, one can estimate the natural frequency of a bridge indirectly from vehicle acceleration response when it crosses a bridge. In this paper, we apply this concept to estimate the bridge fundamental frequency indirectly using the response of a passing instrumented vehicle. The paper first describes analytical formulation and finite element simulation to demonstrate the feasibility of the method. Afterwards, it describes an experimental verification as a proof-of-concept of the method on a full-scale simply-supported short span bridge by using a light commercial vehicle instrumented with accelerometer. Dynamic responses of the vehicle while passing the bridge are recorded and analyzed. Spectra analysis of the vehicle responses reveal that the first natural frequency of the bridge can be estimated with reasonable accuracy when the vehicle moves with constant velocity. The concept of indirect frequency estimation is useful for assessment of short and medium span bridges where permanent instrumentation and routine visual inspection can be too costly. In this method, one can use inspection vehicle instrumented with vibration sensor to conduct periodic measurements by passing the vehicle over several monitored bridges and estimate their fundamental frequencies. When significant change in frequency is detected, detail inspections can be further conducted to investigate the possible damage on the bridge.