【作者】 徐俊；

【导师】 陈惟珍；

【作者基本信息】 同济大学 ， 桥梁与隧道工程， 2006， 博士

【摘要】 在斜拉桥结构体系中拉索寿命最短，斜拉桥在其设计基准期内需实施多次换索工程。因此有必要对退化拉索的承载力和剩余使用寿命展开分析，确定最佳换索时间。根据实桥检测研究，钢丝锈蚀和开裂是决定拉索承载力和剩余使用寿命的致命性因素，其它病害对拉索的影响都可以忽略。钢丝损伤的主因是锈蚀，因此将拉索承载力和剩余使用寿命分析过程分解为三个步骤：根据检测结果模拟拉索锈蚀分布；根据钢丝的锈蚀程度确定钢丝的承载力；根据钢丝的承载力评估整索的承载力和剩余使用寿命。为进行拉索锈蚀程度检测，首先根据钢丝外观将钢丝的锈蚀程度划分为8个锈蚀等级。为找出拉索的锈蚀分布规律，对实桥拆换下来的拉索进行了锈蚀程度检测，发现钢丝的锈蚀程度与到护套破损位置的距离有关。在拉索截面表层钢丝的周向上，钢丝的锈蚀程度随到护套破损位置的距离增加而降低；在拉索截面径向上，钢丝的锈蚀程度由外向内逐渐降低。比较相邻钢丝的锈蚀程度变化关系，发现在这两个方向上钢丝的锈蚀程度都是按指数形式递减的。根据以上检测规律确定了拉索截面锈蚀分布模拟方法：首先对护套破损位置暴露出的表层钢丝进行检测，确定这些钢丝的锈蚀程度；根据护套位置钢丝锈蚀程度模拟截面周向上其它钢丝的锈蚀程度；根据截面周向上的钢丝锈蚀程度模拟径向上的钢丝锈蚀程度。钢丝的损伤演化过程包括6个阶段：钢丝完好阶段、镀锌层锈蚀阶段、钢丝均匀锈蚀阶段、钢丝孔蚀阶段、钢丝腐蚀疲劳阶段和钢丝应力腐蚀阶段。在孔蚀阶段、腐蚀疲劳阶段和应力腐蚀阶段，钢丝都可能失效断裂。钢丝在各阶段的失效机理是不同的，但导致钢丝力学性能降低的原因是相同的：钢丝截面积降低或外形改变导致局部应力集中。因此可以用一个模型描述钢丝的损伤演化过程。这个模型包含两个参数：等效裂纹深度和等效截面直径。在钢丝进入腐蚀疲劳阶段以前，钢丝损伤演化模型的两个参数仅与钢丝的锈蚀程度有关，应根据钢丝的锈蚀程度推算。当钢丝达到腐蚀疲劳阶段后，结合锈蚀程度以及腐蚀疲劳裂纹扩展理论分析了等效裂纹深度的计算理论。为计算拉索的承载力，可将拉索简化成一个串并联系统：拉索由高强钢丝并联构成，而高强钢丝由不同锈蚀程度的钢丝单元串联构成。当拉索内锈蚀分布已知，首先根据钢丝损伤演化模型计算钢丝单元的力学性能，然后根掘串并联规律就可得到拉索的承载力。在研究过程中，还发现拉索的承载力不仅与钢丝的强度有关，还与钢丝的伸长率有关。随着拉索的伸长量不断增加，拉索的承载力经历一个先升高，后降低的过程。在这个过程中，极限伸长率低的钢丝不断地断裂失效。拉索的极限承载力由那些极限伸长率相对较高的钢丝提供。为评估拉索的剩余使用寿命，在拉索损伤演化模型中考虑钢丝锈蚀速度的影响，分析拉索在不同寿命下的极限承载力，认为当极限承载力低于拉索的失效判据时拉索就达到了剩余使用寿命。更多还原

【Abstract】 Stayed cables are vulnerable to rupture, which leads to high maintaining cost during the life time of cable stayed bridges. To ascertain the cable replacing, it is necessary to assess the remained strength and life of deteriorated cables.While all kinds of cable degradations are assessed, the wire degradation was found out to be the fatal cause which leads to the decreasing of cable life. Wire degradation mainly results from corrosion. The process of strength assessment of deteriorated cables includes three steps: simulating the corrosion distribution of wires, calculating the strength of corrosion wires, evaluating the strength and remained life of cables.In order to evaluate wire corrosion practically, 8 corrosion levers are developed according to the appearance of damaged wires. The corrosion distribution state of replaced cables was inspected and the results were provided. The corrosion degree of the wire is affected by the distance between the sheath breakage and wire. Both at the radial direction and at the tangential direction, the corrosion degree degrades exponentially while the distance increases. According to these rules, the corrosion distribution could be simulated with following steps. Firstly, evaluate the corrosion degree of wires at the sheath breakage; simulate the wires at the first layer of cross section; simulate the wires at the radius of cross section.The process of damage evolution of wires includes 6 steps: scatheless wire stage, zinc coat corrosion stage, general corrosion stage, pitting corrosion stage, corrosion fatigue stage and stress corrosion stage. The wire would rupture at pitting corrosion stage, corrosion fatigue stage and stress corrosion stage. At different stages, the deterioration mechanism is different, but the degradation of mechanical properties of wires come from the same reason: the cross section decreasing or stress concentration due to surface roughness. The course of wire deteriorating could be simulated by the damage evolution model of wires, which has two parameters: a, which is equivalent crack depth and d, which is equivalent diameter. Before the corrosion fatigue stage, a and d are influented by the corrosion degree alone, while after the stage, the two parameters are influented by the corrosion and load, which means that a should be calculated according to the CFCP theory.Stayed cable may be considered as a parallel series system in which the cable consists of parallel wires and the wires are formed of wire elements in series. After the corrosion distribution being simulated, the mechanical properties of wire elements could be calculated according to the damage evolution model of wires, so do the strength of cane according to the deteriorated cable model. The strength of cable is affect not only by the strength of wires, but also by the ultmost elongation of wires. The strength of cable experience a period which increase at first and, then decrease, while the elongation of cable increases. During the period, wires full breakage gradually when the elongations of wires are less than the elongation of cable.For the porpose of evaluation the service lives of cables, the ultmost strengths of cables in different stage are calculated when the corrosion rate is counted. The Cables will fall rustily when the strengths achieve the failure criterion.更多还原