车辆超载与氯盐侵蚀复合作用下钢筋砼梁桥的疲劳时变可靠度分析

Traffic overload and chloride-induced corrosion are the main problems for highway bridges in China. Combinational action of overloads and chloride-induced corrosion will lead to accelerate deterioration of fatigue performance for existed Reinforced Concrete (RC) beam bridges, and shorten its service lifetime. This project will use "corrosion → overload→ corrosion"or "overload → corrosion→ overload" model tests to reveal accelerated deterioration mechanism of fatigue performance for material and key element of RC beam bridge.Stochastic characteristics of factors afecting fatigue performance are analyzed.Then probabilistic fatigue deterioration models of key material and elements of RC beam bridge are built. Overload-induced fatigue lifetime prediction method of RC beam bridge under chloride ingress can be developed. A random process mdoel of overload effect is proposed based on bridge weight system. Taking contionuous actions of environmental variables and discontionuous load of overloads into accounts, generalized integral theory based computional method for reliability index is developed. Then the fatigue reliability assessment method of RC beam bridge under chloride environments is proposed considering traffic overload effect. This work will provide a theory basis for maintenance and management of bridges under overloads.

车辆超载和环境侵蚀是我国公路桥梁面临的现实问题。车辆超载和环境侵蚀的复合作用将导致公路桥梁疲劳性能退化加剧、服役寿命缩短。本项目以量大面广的公路钢筋砼梁桥为工程背景，选取氯盐侵蚀为环境侵蚀代表因素，统计并建立随机超载疲劳荷载谱；结合"腐蚀→超载→腐蚀"和"超载→腐蚀→超载"等试验研究和理论分析，揭示车辆超载和氯盐侵蚀复合作用下钢筋砼梁桥的材料和构件疲劳性能的退化规律，分析其影响参数的时变随机特征，从而建立桥梁材料和构件疲劳损伤退化概率模型；提出车辆超载和氯盐侵蚀复合作用下钢筋砼梁桥疲劳寿命预测方法；考虑环境变量的连续作用特征和超载车辆的间歇反复作用特征，提出相应的疲劳时变可靠度实用计算方法，为我国现有超载状况下桥梁的服役安全评估和科学维护管理提供理论基础。

针对RC梁桥在车辆超载与环境侵蚀介质复合作用下疲劳性能退化的问题，本课题基于车辆荷载长期监测数据，提出一种优化高斯混合概率建模方法。在此基础上采用影响线法和极值外推理论，对服役期RC梁桥的荷载效应水平进行了预测，从而得到试验所需的疲劳荷载水平。研究了混凝土抗压强度在不同侵蚀环境下的退化规律和破坏模式。在试验分析基础上，构建了混凝土剩余强度在腐蚀及疲劳荷载作用下的退化模型。将分形维数及尺度系数相结合，得到了锈蚀钢筋表面特征参数，并在此基础上给出了三维腐蚀形貌表面特征参数的计算方法。根据特征参数可以表征锈蚀形貌且不会忽略细节特性的特征，寻找特征参数与极限强度、屈服强度、疲劳寿命间的函数关系，建立了基于分形理论的锈蚀钢筋本构关系模型。基于材料层面的疲劳剩余强度退化规律及理论分析，通过建立疲劳次数与锈蚀程度与钢筋及混凝土剩余强度的方程，得到了材料在锈蚀与疲劳复合作用下的剩余强度计算模型。