Non-Contact bridge deflection measurement : application of laser Technology

Abstract

Structural deflections represent a critical response parameter often measured for structural health monitoring. Traditional measurement sensor technologies such as DCDTs, LVDTs, etc., require attaching the device between the point of measurement and a reference point. Generally, this requires connecting the sensor to the ground or a temporary structure such as scaffolding. Use of the traditional sensors for highway bridge deflection measurement poses many challenges as most of them are over either a road or a waterway. Because of these challenges, they are not often used and deflection is calculated either from indirect data such as girder end rotation or the structural parameters that contribute to deflection which is derived from measurements such as strain and curvature. Strictly speaking, measured displacements provide the best means for understanding structural behavior. Aiming at addressing the challenges of direct measurements of bridge deflections, this article will address the capabilities of two state-of-the-art non-contact measurement technologies. These technologies are: Laser Tracker and Laser Scanner. Laser Tracker records position coordinates at few discrete points while the laser scanner captures point clouds representing deformed and undeformed shapes of a structure. These two remote technologies present distinctive advantages, capabilities, limitations, and several challenges for field applications. The article will present a case study where laser tracker and laser scanner was collaboratively used to measure the deflection of a highway bridge under static truck loads. Further, the capabilities, limitations, and several challenges for field applications of these technologies will be summarized.