Study on the dynamic properties of a suspended bridge using monocular digital photography to monitor the bridge dynamic deformation

This study makes use of monocular digital photography, based on the IM-STBP (image matching-space time baseline parallax) method, to monitor bridge dynamic deformation to study bridge dynamic properties. A bridge was first photographed when traffic light was red (i.e., when the bridge was not influenced by dynamic vehicle load) to generate the zero image (a.k.a. the reference image), and then photographed every 3 s when the traffic light was green (i.e., when the bridge was influenced by dynamic vehicle load) to produce image sequences as successive images. Relative deformation values of deformation points were obtained based on the IM-STBP method. The results show that the measurement accuracy of the IM-STBP method reaches a sub-pixel level (0.445, 0.470 and 0.705 pixels in the X, Z and comprehensive directions, respectively) and that maximal deflections of the bridge monitored by cameras 1 and 3 (37.22 and 47.40 mm, respectively) are within bridge deflection tolerance (75 mm). The monocular digital photography presented in this study has proved effective in monitoring bridge dynamic deformation even when the photographing direction is not perpendicular to the bridge plane and useful in assessing the situation of a bridge by monitoring the instantaneous dynamic global deformation of a bridge when the traffic light is green. Deformation curves in real time can also provide warning of any possible danger on the bridge. These global deformation curves of a bridge play a key role in studying the dynamic properties of a bridge influenced by dynamic vehicle load.