Detection of fatigue crack of steel deck plate by ultrasonic nondestructive testing

Fatigue cracking in the welded joints of the orthotropic steel deck plate is one of the most serious problems in Japan. Cracking of many of the bridges occurred after about 20 years of service period. Among fatigue cracks reported in the deck system, rib-to-deck crack is very important to detect, because the crack results in decrease of the serviceability to the traffic. Nondestructive technique is essential because the visual inspection is not possible in the closed rib. The objective of this study was to investigate the applicability of ultrasonic testing. Ultrasonic techniques applied in this study was the creeping wave technique and the horizontal shear wave (SH wave) technique, and surface (Rayleigh) wave technique. Fatigue tests were conducted by a specimen that had the same configuration as the actual orthotropic steel deck. After every some hundred thousand cyclic loading, the ultrasonic testing was conducted. The SH wave technique showed the best detection ability among those techniques. The ratio of detection for cracks of 2 mm or longer was 100 %. The creeping and surface wave techniques also showed a good performance. The ratios of detection for a crack of 2 mm or longer were 80 and 75 %, respectively.