Dynamic Displacement Measurement of a Long-span Bridge Using Vision-based System

Displacement data under operational loads are an important aid for the estimation of structural performance, but accurate measurement of structural displacement remains as a challenging task, especially for long-span bridges. This paper describes a displacement monitoring test of a suspension bridge (Humber Bridge, UK) using vision-based system and GPS. A prefabricated planar target was attached to the mid-span of bridge to aid camera calibration. The target was tracked based on normalized grey-scale correlation (NGC) and super resolution techniques. The vertical and transverse displacement at mid-span in operation condition was recorded and the optical system was identified to be an effective way for measurement at very long range. The GPS measurement showed the accuracy of centimetre level, which was undesirable for the possible applications in structural identification. The exercises showed that better measurement of bridge displacement could be obtained by fusing GPS data with the collocated acceleration data using Kalman filter.