ABSTRACT
There are two recognized methods for the evaluation of the remaining strength of cables based on internal inspection findings and testing results, NCHRP Report 534 Guidelines (Report 534) and the BTC method. Report 534 provides visual-based assessments of the corrsion on wire surface. The Guidelines assign a proportion of the cable cross-section to each of the stage of corrosion observed in the wedge openings. The evaluation of Report 534 then proceeds with the evaluation of remaining strength based on wire sample test results and the hypothized proportions of the stages of corrosion in the cable cross-section. The BTC method provides a reliability-based evaluation of the remaining strength and residual service life of cables. The method includes random sampling without regard to wire appearance, mechanical testing of wire samples, determining the probability of broken and cracked wires, and fracture-based analysis of cracked wires. The probabilistic-based method forecasts the residual life of the cable by predecting the increasing rate of detrioration and strength degradation. The BTC method is published in the latest FHWA Primer for the Inspection and Strength Evaluation of Suspension Bridge Cables. The BTC method is currently being applied alongside Report 534 Guidelines at the Forth Road Bridge in Scotland. The dual application of the two methods provides the bridge owners with high level of confidence in the estimated cable strength.
