Fatigue crack sizing in steel bridge decks using ultrasonic guided waves

A baseline-free quantitative sizing methodology utilizing ultrasonic guided waves for fatigue cracks under welded stiffeners in steel bridge decks has been developed. An inverse wavefield extrapolation based formulation for obtaining the crack reflectivity and depth profile has been presented in the kernel of which, the presence of welded orthogonal stiffeners has been accounted for. Having conducted experiments on a test bridge deck subject to fatigue loading, it has been demonstrated that the crack profile can be estimated from the reflection coefficients obtained. In comparison with the reference measurements, the maximum crack depth estimation error turned out to be about 20%