Vehicle Scanning Method for Bridges

6Effect of Road Roughness on Extraction of Bridge Frequencies

The vehicle scanning method for measuring bridge frequencies is a potentially powerful technique for its mobility, movability, and economy, compared with the conventional technique that requires vibration sensors to be directly installed on the bridge. However, road roughness may pollute the vehicle spectrum obtained and render the bridge frequencies unidentifiable. The objective of this chapter is to study such an effect. First, a numerical simulation is conducted using the vehicle−bridge interaction (VBI) element developed previously to demonstrate how the road roughness affects the vehicle response. Then, an approximate theory in closed form is presented, for physically interpreting the role and range of influence of road roughness on the identification of bridge frequencies. The latter is then expanded to include the action of two connected vehicles of identical frequency moving over the same roughness. It was found that by deducting the response of one vehicle from the other, the identifiability of bridge frequencies will be enhanced in the residue vehicle response. This chapter are based primarily on Yang et al. (2012a,b), with slight modifications on some equations according to Chapter 3.

6.1 Introduction

As previously described, the direct approach identifies bridge frequencies through vibration sensors deployed on the bridge. This approach is the one frequently adopted by researchers and engineers. In ...