On the use of a passing vehicle for the estimation of bridge mode shapes

This paper presents a novel algorithm for the estimation of bridge mode shapes using the response measured on a passing vehicle. A truck-trailer system is assumed, equipped with an external excitation at a frequency close to one of the bridge natural frequencies. The excitation makes the bridge response dominant at its natural frequency. The acceleration responses are measured on two following axles of the vehicle. It is shown that the amplitude of the signal includes the operational deflected shape data which can be used to estimate the bridge mode shapes. The energy of the responses measured on two following axles is obtained using the Hilbert Huang Transform. It is shown that the bridge mode shape can be estimated with high resolution and accuracy using a rescaling process. The presence of road roughness introduces additional contributions to the response measured on the vehicle, in addition to the bridge response. The concept of subtraction of the responses measured from two identical axles is used to remove the effect of road roughness.