SAFETY ANALYSIS OF SUSPENSION-BRIDGE CABLES - WILLIAMSBURG BRIDGE

The Williamsburg Bridge crossing New York City's East River has been attacked both by engineering critics who consider it a clumsily oversized design and by the harsh salt-air environment around the island of Manhattan, which has infiltrated and corroded its steel main suspension cables. At one point in 1988, the bridge was judged to be irreparably damaged by corrosion and in need of full replacement. This paper presents a methodology to estimate the current safety factor of the main suspension cable, based on wire samples extracted from the cable and tested in a laboratory for tensile strength and elongation. The methodology estimates the cable safety factor using the ductile wire and the ductile-brittle wire models, following two different approaches within each one model: a Monte Carlo simulation approach and an extreme-value-distribution approach. It is concluded that the ductile wire model in conjunction with the extreme-value-distribution method provide the best estimate for the cable safety factor with the least computational effort. This estimate for the safety factor is in the range 4.19-4.23.