Failure cause of bridge tie-down cables after 30 years of service

Abstract

The paper approaches the sensitivity to stress corrosion cracking of zinc-coated, high-strength, eutectoid steel wires extracted from collapsed prestressing strands after 30 years of service as tie-down cables of a cable-stayed bridge. The observed damage of wires consisting of pitting corrosion, cross-section losses and even failure, varied in intensity from one cable to another and allowed the assessment of the effect of damage level on the mechanical behavior of wires, as well as that of the susceptibility of the galvanized wires to aggressive environments. The results were obtained by performing fracture tests of service-damaged wires under constant load and under increasing load at low strain rate, while exposed to an aggressive media (ammonium thiocyanate - FIP solution). The SEM analysis of the fracture and lateral surfaces of the tested wires proved the similitude between the service and laboratory-induced damage. It also provided evidence of hydrogen embrittlement in the failure mechanism of the wires. Accordingly, the service ruptures were attributed to progressive cracking by environmentally assisted, hydrogen embrittlement propitiated by the partial dissolution and cracking of the zinc coating in the tensioned wires.