Vehicle Scanning Method for Bridges

2Vehicle Scanning of Bridge Frequencies: Simple Theory

The frequencies of bridge vibration represent a kind of information most useful to modal identification and health assessment of bridges. Traditional vibration tests aimed at measuring the bridge frequencies, known as the direct approach, require installation of certain vibration sensors and data logger on the bridge, which is not only costly but also inconvenient. The idea of using a moving test vehicle to extract the dynamic properties, particularly, the frequencies of a bridge was first theoretically attempted by Yang et al. (2004a). This approach was previously known as the indirect approach and renamed as the vehicle scanning method for bridge measurement. In this chapter, the simplest and fundamental theory for extracting bridge frequencies from a moving test vehicle is presented. In order to identify the key parameters dominating the vehicle‐bridge interaction (VBI) response, while unveiling the key phenomena involved, assumptions that lead to closed‐form solutions are adopted. Particularly, a vehicle is modeled as a sprung mass, and a bridge as a simply supported beam. Only the first mode of bridge vibration is included in the formulation. The concept of extracting bridge frequencies from a passing vehicle, however, is not restricted by these assumptions, as will be demonstrated in the finite element analysis with virtually no assumptions. The materials presented in this chapter are based primarily on the paper ...