Remote sensing of a cable stayed bridge through displacement influence line

In this paper, non-contact sensing is adopted to monitor the health state of a cable-stayed bridge. Displacement influence line (DIL) of the bridge is remotely identified through several field investigations under the live load tests. DIL is simultaneously obtained for a discrete number of target points once the bridge is in its intact condition. Three different remote sensing techniques including, the laser scanning, terrestrial robotic total station and digital levelling are adopted for this purpose which provides a low-cost and easily deployable monitoring system. A damage is emulated on the bridge by locating a large stationary mass on the bridge to change the condition of the bridge. A drop of only 1% is observed in the fundamental frequency of the bridge as a result of the induced change. DIL of the damaged bridge is remotely identified and the change in DIL is employed as damage indicator. It is demonstrated that DIL is a robust indicator of change in bridge condition and can be used for detection and localization purpose. Further, three-dimensional finite element model of the bridge is established in ABAQUS platform; the model is calibrated using the measured static and dynamic responses of the bridge. Several damage scenarios are induced in the numerical model and it is further verified that the DIL is a robust indicator of damage in the bridge.