Effect of Road Surface Roughness on Extraction of Bridge Frequencies by Moving Vehicle

Measuring the bridge frequencies indirectly from a test vehicle passing the bridge is featured by its mobility, economy and promptness, compared with the conventional technique that requires vibration sensors to be mounted directly on the bridge. However, the road surface roughness may pollute the vehicle spectrum, rendering the bridge frequencies invisible. This paper is aimed at studying such an effect. First, a numerical analysis is conducted using the vehicle-bridge interaction element to demonstrate how the surface roughness affects the vehicle response. Then, an approximate theory in closed form is presented for physically interpreting the influence of surface roughness on the identification of bridge frequencies. To reduce the effect of surface roughness, two connected, identical vehicles are allowed to travel the bridge, with the response recorded and synchronized for one vehicle subtracted from the other. It was demonstrated that the visibility of the bridge frequencies can be greatly enhanced in the residue response.