Simultaneous Identification of Fundamental Frequency, Mode Shape, and Damping of a Bridge by a Passing Vehicle-Trailer System

Abstract

A theoretical framework is proposed to identify fundamental frequency, mode shape, and damping of a bridge simultaneously by a passing vehicle-trailers system with only accelerometers. The framework is the first attempt to use indirect method to identify all fundamental modal properties of a bridge simultaneously without shaker, laser sensors and pre-known information. The vehicle performs as both “tractor” and “excitor” and the trailers perform as “message carriers”. The residual response defined as the response difference of one trailer to another one was usually adopted in the previous studies to remove the adverse effect of road roughness; however, it lacks theoretical support. Instead, the residual response of one trailer–bridge contact point to another one is used in this study, and theoretical analysis proves that it can effectively eliminate the adverse effect of road roughness. Different from previous studies, the residual response of contact point in this study is obtained in the frequency domain rather than the time domain. Frequency and damping can be evaluated by applying single degree-of-freedom (SDOF) model-based curve fitting technique to several discrete values from the Fourier transform of the residual response. Mode shapes can be reconstructed by dividing the Fourier transform of one residual response at the natural frequency by another one without time lag. The proposed framework is validated by independent finite element (FE) analysis and it shows great performance. Parametric study including vehicle speed, measurement noise, calibration error, road surface roughness and boundary condition has also been conducted to check its feasibility in various scenarios.