During an evaluation of the cables on the Severn Bridge in the United Kingdom (UK), modifications to the cable strength equations given in the NCHRP Report 534, “Guidelines for Inspection and Strength Evaluation of Suspension Bridge Parallel-Wire Cables” were made to better evaluate the cable strength. The corrosion of the wires was advanced, with as many as 163 broken wires being observed in one of the panels. When an isolated panel is inspected, as is common in a first inspection, nothing is known about adjacent panels, and the Guidelines require that the number of broken wires in the adjacent panels be assumed to be the same as in the inspected panel. This can lead to underestimating the cable strength when a large number of broken wires is found. A modified algorithm was developed to eliminate this underestimate. A further modification was made in which the actual calculated coefficient of redevelopment is used to calculate the stress that is redeveloped in a broken wire, unlike the single value of this coefficient corresponding to the effective development length assumed in the Guidelines. When this modification is used, the calculations will show that some wires have a redeveloped stress greater than the failure stress of the entire cable, and an additional correction is introduced for this condition.An example is given, and guidance for the conditions under which these modifications should be used is also given. These modifications will be of interest to cable evaluators when a severely deteriorated cable is found.
Abstract