Crack detection in steel girders of bridges using a broken wire electronic binary sensor

Abstract

North American infrastructure, including steel bridges, are aging and reaching the end of their service lives. Over time, environmental stresses and cyclic truck traffic over bridges may lead to crack formation and crack propagation in the steel girders used in bridges. Cracks in steel girders decreases the load bearing capacity of the superstructure and may lead to failure of the structure. Existing methods of crack detection can not be practically deployed over larger structures. There is a need for a low-cost distributed crack sensing system. Given the critical nature of bridges, a continuous monitoring system would be preferred. Available continuous monitoring systems, such as Fiber Optic Sensors (FOS) are expensive which makes them unfeasible to be used for most of the bridges. In this paper, a new low-cost and accurate Binary sensor for detecting cracks in steel girders is discussed. The Binary sensor is comprised of wire bonded onto the girder using an adhesive. When the girder cracks, the crack is coupled to the wire, via the adhesive, causing it to also crack. The sensing system detects the open circuit in the wire created by the crack. A critical figure of merit for this system is the minimum crack width required to cause the wire to break. In the present work, cracks of less than 0.2 mm width can be reliably detected on steel girders.