A Comprehensive Methodology to Estimate the Current Safety and to Predict the Remaining Useful Life of Suspension Bridge Cables

在美国，包括大跨度缆索悬索桥在内的各种运输系统，由于在维护和延长寿命技术方面的投资不足，特别是由于对结构评估和保护领域的研究支持明显不足，已经被允许恶化。对纽约大都会地区悬索桥主缆的深入检查发现，在悬索桥主缆内部和锚固处有相当数量的断缆，出现了大面积的劣化和脆性断裂。这些发现为确定现有桥梁主悬索的实际强度提出了困难的任务。悬索桥缆索的安全评价一直以缆索强度与计算极限荷载之比作为安全系数。然而，考虑到与电缆劣化模式和电线腐蚀机制有关的许多不确定因素，以及考虑到被检查和/或测试的电线比例相对较小，这种安全系数仅作为初步近似有用，而不适用于评估桥梁的整体安全性。采用可靠性或安全指标等概率指标是衡量主悬索整体安全性的更好、更合适的方法。如果没有一个明确的方法来评估现有缆索的剩余强度，吊桥业主机构就不清楚在缆索检查中要寻找什么，因此他们的维护计划主要基于以前的经验和反复试验的尝试。这笔拨款提议超越NCHRP项目10-57的目标，开发一种全面的方法，对现有悬索桥的电缆系统进行严格的安全评估。本研究的最终目标将集中在：1)根据缆线的检查和实验室测试结果估计悬索桥主缆的实际剩余强度和实际安全性；2)使用相同的结果预测悬索桥缆线的剩余使用寿命。这样，就可以直接比较不同桥梁的电缆的总体安全性。还将开发一种新的电缆模型，该模型考虑了腐蚀桥线的有限和不同的延展性，使用概率框架来考虑劣化模式的随机性。用于新预测模型的统计参数的确定将使用一组独特的检查和测试数据，这些数据是由哥伦比亚大学卡尔顿实验室收集的30多年的桥梁测试数据，以及当前研究项目的钢丝劣化结果。该项目将对桥梁工程界做出重大贡献，对现有悬索桥主缆的整体安全性和剩余使用寿命进行更严格的描述。

In the US, various transportation systems, including long-span cable suspension bridges,have been allowed to deteriorate because of inadequate investment in maintenance and life extension technology, and particularly because of clearly insufficient support for research in the area of structural assessment and protection. In-depth inspections of the main cables in the suspension bridges in the New York metropolitan area have found a quite large number of broken wires inside the cables and at the anchorage, showing extensive deterioration and brittle fractures. These findings pose the difficult task of determining the actual strength of main suspension cables in existing bridges. The safety evaluation of suspension bridge cables has always been done considering as a safety factor the ratio between the estimated cable strength over the computed ultimate load. However, in view of the many uncertainties involved with the cable deterioration pattern and with wire corrosion mechanisms, and considering the relatively small proportion of wires that are inspected and/or tested, such a safety factor is useful only as a first approximation, but not in assessing the overall safety of the bridge. A better and moreappropriate measure of the overall safety of main suspension cables is the use of probabilistic indicators such as the reliability or the safety index. Without a well-defined methodology for estimating the residual strength of an existing cable, suspension bridge owner agencies do not have a clear idea of what to search for in a cable inspection and so they base their maintenance program mainly on previous experiences and on trial and error attempts. This grant proposes to go beyond the objectives of the NCHRP Project 10-57 by developing a comprehensive methodology for a rigorous safety appraisal of the cable system in existing suspension bridges. The ultimate objectives of this study will focus on 1) the estimation of the actual residual strength and of the actual safety of main cables in suspension bridges based on results of inspections and laboratory testing of cable wires, and on 2) the prediction of the remaining useful life of suspension bridge cables using the same results. In this way, the estimated overall safety of the cables of different bridges can be directly compared. A new cable model that accounts for limited and different ductility of the corroded bridge wires will also be developed, using a probabilistic framework to account for the random nature of the deterioration pattern. The determination of the statistical parameters to be used in the new prediction model will be done using a unique set of inspection and test data, collected over 30 years of bridge testing by the Carleton Laboratory at Columbia University, and on the results of current research projects on wire deterioration. This project will make a significant contribution to the bridge engineering community with the introduction of a more rigorous description of the overall safety and remaining useful life of main cables in existing suspension bridges.