Monitoring for fatigue crack geometry in orthotropic steel bridge decks by application of reflected Lamb waves

Orthotropic steel bridge decks (OSDs) have been widely used as a crucial load-bearing structures in long-span bridges,. However, the weld connections in OSDs are susceptible to fatigue crack initiation due to the high stress cycle caused by vehicle loads. Reflected Lamb waves have potential in the monitoring of crack geometry, and different sensor arrangements are employed for different crack types in OSDs. Three full-scale specimens were fabricated and tested with the recommended sensor arrangements to continuously monitor two types of cracks in tests. Finite element models were also established and verified by the experimental results. Parametric studies were conducted to investigate the effects of sensor arrangements, crack lengths and angles on monitoring results. A wavelet transform algorithm was applied to analyze reflected waves and extract standardized wave features, based on which the crack geometry was evaluated. The experimental results reveal that the standardized wave features from the reflected Lamb waves change significantly with the increase of fatigue life, indicating that the features are sensitive to fatigue crack growth. The simulation results reveal that the standardized wave features effected by crack geometry are positively correlated with projected crack lengths perpendicular to the direction of wave propagation. The optimal arrangements of wave sensors for crack monitoring at deck-to-rib connections are to place excitation and reception sensors at 200 mm and 60 mm from the welds at crack initiation plates, respectively; while for cracks at rib-to-floorbeam connections, excitation and reception sensors are located at 200 mm and 50 mm distant from the horizontal welds at cut-out, respectively, and all sensors are 50 mm distant from vertical welds.

Automated summary

This study investigates the monitoring method for fatigue cracks in orthotropic steel bridge decks (OSDs). Experimental and numerical simulation results show that reflected Lamb waves have potential in monitoring crack geometry. The sensor arrangements and crack dimensions have effects on the monitoring results. Standardized wave features are sensitive to fatigue crack growth.