Vehicle Scanning Method for Bridges

9Theory for Retrieving Bridge Mode Shapes

This chapter presents a theoretical framework for constructing the bridge mode shapes from the dynamic response of a passing test vehicle. Compared with the conventional approaches that only measure a certain number of points (with sensors) on the bridge, the current approach offers much more spatial information, and therefore higher resolution, in retrieving the mode shapes, as the test vehicle can virtually touch each point along its path on the bridge. Basically, only one or few sensors need to be installed on the test vehicle. Factors that affect the accuracy of this approach are studied, including the vehicle speed, random traffic, and road surface roughness. Through numerical simulations, the approach is verified to be feasible under the condition of constant and low vehicle speeds. The materials presented in this chapter are based primarily on Yang et al. (2014) with some modifications according to Chapter 3.

9.1 Introduction

Measuring the mode shapes of a bridge is a crucial task in bridge engineering, since the measured mode shapes serve as a useful index for many applications related to bridges, such as numerical model calibration and updating (Brownjohn et al. 2001; Jaishi and Ren 2005; Altunisik et al. 2012), structural health monitoring and damage detection (Doebling et al. 1998; Farrar et al. 2001; Chang et al. 2003; Carden and Fanning 2004; Chrysostomou et al. 2008), and so on. Conventionally, to measure the mode shapes ...