Because of the complexity of the technical information presented in NCHRP Report 534, the FHWA published a Primer for the Inspection and Strength Evaluation of Suspension Bridge Cables in May 2012 to supplement NCHRP Report 534. The Primer, with much of the information taken directly from NCHRP Report 534, offers an initial resource for agencies planning and performing inspections, metallurgical testing, and strength evaluations of suspension bridge main cables. The Primer also presents “BTC Method for Evaluation of Remaining Strength and Service Life of Bridge Cable” in the appendix as an alternative methodology to that provided in the NCHRP Report 534, for the evaluation of bridge cable remaining strength and its residual life. In addition, the Primer states that the AASHTO LRFR method is not yet applicable to the rating of suspension bridge cables since LRFR calibrations have not been performed to date for suspension bridges. The other concern is that the current LRFR calibration is designed for bridges with dead load to live load ratios generally not higher than about 2 to 1. For major suspension bridges, however, the dead loads may be higher than the live loads by a factor of 5 or more.
The objective of this research is to improve the current industry practice in inspection and strength evaluation of existing suspension bridge main cables in the following areas: (1) optimization of the main cable opening frequencies and wire sampling methodologies to minimize the potential damage to existing cable wires; (2) resolving the discrepancies in evaluating the main cable remaining strength when using alternative methods such as the BTC Method and the Random Field-Based Approach to increase the confidence in predicting the main cable remaining strength; (3) adopting a reliability-based evaluation methodology consistent with LRFD and LRFR philosophy to verify that the cable target failure probabilities are not exceeded with the consideration of the main cable remaining strength as well as the applied load effects; and (4) advancing the state-of-the-art NDE and SHM techniques to reduce our dependence on cable opening and wire sampling in main cable inspection and strength evaluation.