Vehicle Scanning Method for Bridges

5EMD‐Enhanced Vehicle Scanning of Bridge Frequencies

The method previously proposed for extracting the bridge frequencies from a passing vehicle works mainly for the first frequency. In order to extract bridge frequencies of higher modes, the vehicle response will first be processed by the empirical mode decomposition (EMD) to generate the intrinsic mode functions (IMFs), and then by the fast Fourier transform (FFT) to extract the bridge frequencies. One feature with the EMD technique is that frequencies of higher modes can be made more visible by the sifting process. To verify the feasibility of such an approach, the vehicle response generated by the finite element simulations will first be analyzed, with results compared with the analytical ones. Then the same procedure will be adopted to extract bridge frequencies from the recorded response of a passing vehicle, and the results will be compared with those from an ambient vibration test. It was demonstrated that using the IMFs computed from the vehicle response, rather than the original vehicle response, bridge frequencies of higher modes can be successfully extracted. The materials presented in this chapter are based primarily on Yang and Chang (2009a), but with slight modifications according to Chapter 3.

5.1 Introduction

The frequency of vibration is an important parameter for bridges, since it relates closely to the overall stiffness of the bridges. A drop in the frequency of vibration reflect on the structure’s health, ...