ABSTRACT
Fatigue cracking of the orthotropic steel deck system has been one of the serious problems. This study focuses on rib-to-deck weld of a trough rib. Nondestructive testing is necessary, because a fatigue crack is initiated at the weld root of a closed section, and visual inspection is practically impossible. Recently, the phased array ultrasonic test systems have been developed and applied in some fields This study aims at the development of a phased array system and investigates the applicability to the rib-to-deck weld of two types of fatigue cracks; one is deck crack and the other is bead crack. The system consists of two phased array transducers, fl w detector, personal computer, and a scanner. Two transducers were set on a deck plate and a rib plate to detect deck and bead cracks, respectively. The number of elements that can be excited and received at a time was 128. Two types of specimens considering deck and bead cracking were prepared. Fatigue tests were carried out. At every 100 kilocycles, the specimen was taken out of the test site, and ultrasonic tests were applied. In the next step, the amplitude of loading was changed in order to make beach marks. Those procedures were repeated until fatigue failure. After failure, a comparison between the actual propagation of a fatigue crack and the result of ultrasonic test was made. Relatively good agreement could be observed, and the result showed that the fatigue cracks of approximately 2 to 3 mm could be detected by the phased array ultrasonic test system.
