AUGUST 13, 2014 – 10:10-10:50 HALL 1
BTC Method for Evaluating Service Life of Bridge Cables
Cable–supported bridges are essential transportation links for regional, national and international commerce and lifelines. As these strategic structures advance in age, they must undergo in-depth evaluations todetermine their condition and load-carrying capacity. Therefore it is essential to have a comprehensive methodology to estimate service life of main cables and to take proactive maintenance steps to extend their service life. This keynote address presents the BTC method; a comprehensive state-of-the-art methodology for evaluation of remaining strength and residual life of bridge cables. The BTC method is a probability-based, proprietary, patented, and peer-reviewed methodology, which applies to parallel and helical; either zinc-coated or bright wire of suspension and cable-stayed bridge cables. The BTC method includes random sampling without regard to wire appearance, mechanical testing of wires, determining the probability of broken and cracked wires, evaluating ultimate strength of cracked wires employing fracture mechanics principles and utilizing the above data to assess remaining strength in each investigated length of the cable. The probabilistic-based BTC method forecasts remaining service life of the cable by determining the rate of growth in broken and cracked wires proportions detected over a time frame, measuring the rate of change in the effective fracture toughness over same time frame, and applying the rates of change to a strength degradation prediction model. The BTC method provides sensitivity analysis to identify the key inputs, which influence the estimated cable strength and assist decision-making process. Dr. Khaled Mahmoud, PE; inventor of the BTC method, is a noted bridge engineer who took part in the design, construction and strength assessment of several landmark cable-supported bridges all over the world. The BTC method has been published, in 2011, in NYSDOT Report C-07-11, cosponsored by the U.S. Federal Highway Administration (FHWA), New York State Department of Transportation (NYSDOT) and New York State Bridge Authority (NYSBA). In 2012, the U.S. Federal Highway Administration included the BTC method in Publication No. FHWA-IF-11-045, “Primer for the Inspection and Strength Evaluation of Suspension Bridge Cables.” The BTC method was applied to determine load carrying capacity of main suspension cables at the Bronx-Whitestone Bridge in New York City, Mid-Hudson Bridge in upstate New York, and the Forth Road Bridge in Edinburgh, Scotland.