疲劳损伤下混凝土节段梁接缝承载力退化机理及评估方法研究

Precast concrete segmental bridges are becoming widely used in the railway and viaduct projects. However, the joint represents the location of discontinuity in segmental beams which may endanger the safety of the whole bridge structure. Currently, the combined shear and bending behavior of joints under static loadings and the resistance deterioration mechanism under fatigue loading have not been further researched. Therefore, the research about the residual resistance of the joints in segmental beams under fatigue loadings and service life safety assessment method will be carried out in this project. Firstly, an experimental research will be performed for the resistance of the joint in segmental beams under combined shear and bending. The effects of the joint type and span-depth ratio on the joint resistance will be analyzed, based on which the calculation formula will be proposed for calculating the resistance of the joint under static combined shear and bending; Secondly, the static loading experiment following the fatigue loading experiment will be carried out to study the residual resistance of the joint under fatigue damage. The deterioration models of the concrete compressive strength, equivalent cross section area of the prestressing tendons and the friction factor within the dry joint section under the fatigue loading are established. The calculation formula can be obtained for the residual resistance of the joints under fatigue damage. Finally, a fatigue damage index is proposed based on the monitoring strain data of the concrete. The relation is fitted between the fatigue damage index and the decreasing concrete strength, equivalent cross section area of tendons and friction force within the dry joint section based on data obtained from the fatigue loading experiment. According to the obtained formula for calculating the residual resistance of the joints under fatigue damage, the service life safety of the joint in segmental beams can be assessed. The main expected results of this research project will provide a theoretical foundation for properly designing the precast concrete segmental bridges and ensuring the service life safety.

预应力混凝土节段式桥梁在城市高架、铁路沿线的应用日渐广泛，而接缝作为主梁构造上的薄弱区域影响结构整体的安全性。目前对接缝局部区域在弯剪耦合作用下的破坏机理及疲劳荷载作用下承载力退化规律的研究不够深入。为此，本项目拟开展对疲劳荷载下节段梁接缝剩余承载力及其服役期安全性评估方法的研究。首先，开展静载下节段梁接缝的弯剪耦合破坏试验，建立不同接缝类型、剪跨比下弯剪耦合承载力分析计算模型；其次，开展疲劳损伤后节段梁接缝的剩余承载力试验，建立疲劳荷载下混凝土强度、钢筋等效截面积和干接缝间摩擦力的退化模型，提出考虑疲劳损伤的接缝剩余承载力计算分析模型。最后，采用混凝土疲劳应变监测数据表示疲劳损伤指标，基于疲劳破坏试验拟合损伤指标与混凝土剩余强度、钢筋剩余等效面积以及摩擦系数间的关系。结合剩余承载力计算模型对服役期节段梁安全性进行评估。本项目的研究成果将为混凝土节段式桥梁的安全运营提供理论和技术保障。

钢筋混凝土节段式桥梁具有工厂化预制质量保证率高、单节段体量小便于运输等优点，在公路及铁路桥梁工程领域具有广阔的应用前景。然而接缝作为节段式桥梁构造上的薄弱区域，其在弯剪耦合作用下的承载力安全性及对结构长期服役期性能的影响还缺少深入研究，阻碍了该桥型的发展。本项目针对上述问题，依次开展了静载作用下混凝土节段梁接缝的弯剪耦合破坏机理研究；锈蚀疲劳耦合下节段梁桥面板承载力退化机制研究；基于监测数据的混凝土节段梁性能评估方法研究，取得了一系列的理论成果。通过开展节段梁接缝截面纯弯、直剪和弯剪耦合承载力模型实验，获取了不同类型节段梁中接缝开展的情况及其对应的开裂荷载值，以及承载力失效时接缝截面的破坏形态及相应的极限承载力。探明了接缝弯剪破坏机理，建立了弯剪耦合作用下节段梁接缝承载力极限状态简化分析模型。针对混凝土节段梁桥面板易受到车载和环境腐蚀共同作用的情况，分析了混凝土桥面板由于车轮荷载作用导致的疲劳开裂的情况，揭示了车载疲劳裂缝对氯离子等环境腐蚀介质向混凝土内部扩散过程的影响，进一步获取了钢筋锈蚀引起的截面内力重分布对钢筋疲劳应力幅及其损伤过程的影响规律，建立基于锈蚀疲劳耦合作用机制的混凝土桥面板承载力分析模型。基于接缝损伤后节段梁接缝截面刚度出现明显的降低的试验结论，根据结构健康监测系统提供的环境温度及主梁挠度监测数据，建立了可考虑温度输入和结构响应输出时间滞后性的相关模型，在此基础上提出了一种桥梁主梁服役性能异常识别方法。本项目取得的相关研究成果能够为混凝土节段式桥梁接缝截面的承载力安全性设计、服役期的安全性评估提供理论依据，有望为混凝土节段式桥梁在公路及铁路桥梁工程领域的推广应用提供助力。