Estimating the Mode Shapes of a Bridge Using Short Time Transmissibility Measurement from a Passing Vehicle

This paper reports on the analysis of the signals sent by accelerometers fixed on the axles of a vehicle which passes over a bridge. The length of the bridge is divided into some parts and the transmissibility measurement is applied to the signals recorded by two following instrumented axles. As the transmissibility procedure is performed on the divided signals, the method is called Short Time Transmissibility Measurement. Afterwards, a rescaling process is accomplished in order to estimate the bridge mode shapes. The numerical results indicate that the method can calculate the mode shapes of the bridge accurately. It is demonstrated that short time transmissibility method does not depend on the excitation characteristics contrary to the other related methods which assume that the excitation should be white noise. Generally, the bridge mode shapes may be invisible due to the excitation exerted by the road profile. This issue is also resolved by subtracting the signals from the successive axles. Finally, the signals are contaminated with noise and the robustness of the method is investigated.