Damage tolerance and failure analysis of tie-down cables after long service life in a cable-stayed bridge

Abstract

The paper examines the damage tolerance of prestressing steel wire-strands failed after being exposed without protection to environmental action for 30 years as tie-down cables of a cable-stayed bridge. The influence of corrosion pitting, cross-section losses and possible assisted cracking on the tensile behavior of the Zn-coated prestressing steel strand-wires was experimentally determined, as well as their susceptibility to aggressive environments. A damage tolerance assessment was completed by performing fracture tests of as-received wire-samples exposed to an aqueous solution of ammonium thiocyanate while tensile loaded by applying a constant load followed by an increasing load at low strain rate. The fractographic analysis of the wires broken in-service and in-laboratory proved the induced damage to be very similar and provided evidence of environmental damage in some of the service ruptures. The damage tolerance assessment is in agreement with the two types of wire ruptures found in the failed wire-strands. These sequentially occurred over the 30 years of service, with the brittle ruptures of the mostly exposed peripheral wires being due to environmentally assisted cracking and preceding the ductile ones of the remaining wires by mechanical overloading.