Laser-Based Detection of Structural Vibrations of a Model Truss Bridge

Undesirable structural vibrations often result in fatigue damages of civil infrastructures. To facilitate structural health monitoring, measurements of dynamic response quantities like velocity and displacement of a structure are needed. This work involves developing a low cost non contact photonic sensor based on laser-photodiode pair that can capture the essential features of the vibrating object under test, in this case a truss bridge (built in-house). Further, we present an algorithm based on wavelet transformation to process the raw data from photodiode to estimate instantaneous velocity of truss bridge subject to impact loading. Finally, a set of twelve measurements involving three different impact loading points on truss bridge and four measurements done at each impact loading points is performed to validate our method. It is experimentally verified that the proposed laser system can detect the velocity associated with small vibration as low as $0.010 \mathrm{~mm} / \mathrm{s}$.