Steel bridges are susceptible to fatigue cracking, and long cracks can potentially lead to catastrophic accidents. The timely detection of fatigue crack and real-time assessment of fatigue crack length are important for bridge health monitoring. This study developed a grid coating sensor for crack monitoring in steel bridges, which is prepared by air spraying technology and can be applied to three-dimensional fatigue details. The grid coating sensor was designed with three components including driving, sensing, and protective layer. The positions of the sensor electrical measurement points were rationally selected in case of unknown crack direction. The response law of the grid sensor to the crack is analyzed by an analogous analysis of the steady electric field and the anti-plane shear force field, which was verified by the finite element model. The impact of geometric parameters and spatial angles of the sensor on the crack-monitoring performance was investigated. Moreover, fatigue tests were conducted to validate the accuracy and applicability of grid coating sensors for crack monitoring in complex structures. Finally, electrical signal stability of sensors is tested in changing temperature environments. The sensor can effectively monitor fatigue cracks in complex steel structures under temperature changes and dynamic loading environments, and has important practical value.
