With drivers in the United States taking 178 million trips across bridges annually according to ASCE’s 2021 Report Card for America’s Infrastructure, ensuring bridge safety is critical. Bridges in the U.S. are tested every 12-48 months depending on the type of bridge, traffic, and age. The welds (or connections) on steel bridges are the most susceptible to fatigue and are also difficult to detect visually. To avoid disrupting operations, inspectors use nondestructive testing on steel bridges, combining quality assurance with materials science. Methods include radiographic testing, ultrasonic testing, acoustic emission testing, and eddy current testing. Using the principle of electromagnetic induction, ECT can detect and evaluate the stress state and microstructure evolution in steel structures. There have been some studies using ECT for bridges, but the conclusions have been inconsistent. 

In this study, researchers Junyuan Xia, Zhiyuan Yuanzhou, Bohai Ji, and Xiao Jiang developed a metal crack eddy current detection system. In their paper, “An Eddy Current Testing Method Based on Magnetic Induction Intensity for Detecting Cracks in Steel Bridge Decks,” in the Journal of Performance of Constructed Facilities, the authors studied the influences of crack width and depth on the detection system’s ability to identify defects by conducting crack tests on simulated bridge decks made of steel specimens covered with rubber layers (simulated asphalt) of various thicknesses. Their findings provide a basis for the crack testing of steel bridge decks using electromagnetic induction. Learn more about this research at https://doi.org/10.1061/JPCFEV.CFENG-4235. The abstract is below.


Steel bridge decks are prone to fatigue cracking due to long-term wheel loading with high cyclic stress. Fatigue cracks threaten the safety of the bridge and even cause collapse, making crack detection very important. Crack detection with little influence on traffic is difficult due to the pavement. To confirm the feasibility of eddy current testing (ECT) for steel bridge fatigue cracks, the key parameters were calculated. The validity of the parameters was verified preliminarily using the finite-element method. An eddy current movement detection device was set up, and a prefabricated crack test was conducted. The influences of crack size and barrier thickness on the detection signal were discussed. The results show that the sampled signal of magnetic induction intensity is more obvious than voltage, and can be used for crack detection. When the direction of a crack is perpendicular to the direction of detected motion, the amplitude of magnetic induction intensity is positively correlated with the width and depth. Crack detection with a 20-mm-thick barrier layer is possible. The barrier layers weaken the strength of the sampled signal, but the variation law of the intensity with crack parameters is consistent with that of no barrier.

Learn more about this new crack detection technique in the ASCE Library: https://doi.org/10.1061/JPCFEV.CFENG-4235.