FSM-Monitoring of Fatigue Crack in Lattice-Stiffened Steel Plate Deck for Bridge Structure

Abstract

For elucidating applicability of FSM (field signature method) on detection of fatigue crack initiation and monitoring of its propagation, a series of fatigue tests on steel plate decks (4,625 × 2,250 mm2) stiffened in lattice-shape by longitudinal and lateral ribs was carried out by using a wheel load traveling test machine. The fatigue crack was observed by visual inspection at the weld toe between the deck plate and the longitudinal rib when the number of wheel load traveling repetition was around 210 thousands. The response of FSM-monitoring, which was the potential difference change between the sensing pins (pair), became clear when the number of the repetition was around 190 thousands. The fatigue crack initiation could be detected by FSM considerably earlier than visual inspection. The fatigue crack propagation such as the direction could also be monitored even though the distance of the sensing pins was extended to 230 mm. On the other hand, the electric field analysis for the virgin situation without any cracks was carried out. The results of analysis indicated that 60 mm length of crack which could not be confirmed by visual inspection could be detected by FSM.