Monitoring fatigue cracks in rib-to-deck joints of orthotropic steel deck using ultrasonic Lamb waves

Fatigue cracks in rib-to-deck joints of orthotropic steel decks (OSDs) endanger the safety of bridges and are difficult to detect. This paper proposes to monitor fatigue cracks using ultrasonic Lamb waves. An OSD specimen instrumented with ultrasonic sensors was fabricated and tested to crack under fatigue loads. Ultrasonic Lamb waves were measured to detect, locate, visualize, and evaluate fatigue cracks using a probabilistic inspection of damage method. A finite element model was developed to understand wave propagation and crack growth process, and utilized to perform parametric studies on the type, position, and severity of cracks. The results indicated that fatigue cracks were effectively monitored by ultrasonic Lamb waves. Errors of crack positions were less than 5 mm. The damage probability distribution increased with the crack depth and crack length. The ultrasonic Lamb waves are more sensitive to toe-deck and root-deck cracks than other modes of cracks in rib-to-deck joints.