考虑车致循环徐变的大跨预应力混凝土箱梁桥时变可靠性评估

In current long-term performance analysis and time-dependent reliability evaluation of long-span prestressed concrete (PSC) box-girder bridges, the deterioration factors, such as static creep, shrinkage and steel corrosion, etc., are usually taken into account, while the cyclic creep of concrete due to frequent traffic loads is neglected. In order to accurately evaluate the working condition of long-span PSC box-girder bridges during their entire service period, this project intends to conduct in-depth study on the mechanism of cyclic creep and time-dependent reliability of long-span PSC box-girder bridges considering the coupled effects of multiple deterioration factors, which include: 1) The mechanism of cyclic creep of concrete is to be revealed based on experiments and the updated model for cyclic creep will be developed, based on which the time-varying effects of PSC box-girder specimens under repeated loads will be investigated. 2) A dynamic finite element model updating method, which takes into account the time-varying damage changes of structures, will be proposed based on continuously updated monitored data. 3) A dimension reduction method for random field simulation will be investigated based on the Karhunen-Loeve expansion. 4) A unified constitutive model will be constructed considering the coupled effects of multiple deterioration factors, and the evolution of long-term performance of long-span PSC box-girder bridges is to be revealed, based on which the theory and efficient calculation method for time-dependent reliability of long-span PSC box-girder bridges is proposed considering the coupled effects of multiple deterioration factors. The research results are expected to provide theoretical basis for the structural health diagnosis, maintenance and rehabilitation throughout the entire lifespans of PSC bridges.

目前在大跨预应力混凝土（PSC）箱梁桥长期性能分析及时变可靠性评估中，通常考虑混凝土静徐变、应力松弛及钢筋锈蚀等劣化因素，而忽略了频繁作用的车辆荷载产生的循环徐变效应。为准确评定大跨PSC箱梁桥服役期内的工作性态，本项目拟对混凝土循环徐变机理以及考虑多重劣化因素耦合作用的大跨PSC箱梁桥时变可靠性开展深入研究：1）基于试验揭示混凝土循环徐变机理，建立循环徐变修正模型；研究反复荷载作用下PSC箱梁的时变效应演化规律；2）基于桥梁长期监测数据，建立考虑结构时变损伤变化的有限元模型动态修正/验证方法；3）提出基于Karhunen-Loeve级数展开的随机场降维模拟方法；4）构建考虑多重劣化因素耦合效应的统一本构模型，并建立多重劣化因素耦合作用的PSC箱梁桥时变可靠度理论及高效计算方法。研究成果可为PSC桥梁结构的健康诊断及维护加固提供理论依据。

目前针对大跨箱梁桥时变可靠度的分析，通常考虑混凝土静徐变、收缩、应力松弛及钢筋锈蚀等因素，而忽略了随机场和车致循环徐变对结构时变性能和可靠性的影响。基于此，本项目对考虑循环徐变等多重劣化因素耦合效应的大跨箱梁桥时变可靠性进行了深入研究。首先，依据实测数据确定了随机场数字特征，探究了随机场参数对结构时变性能的影响，建立了考虑随机场的大跨箱梁桥可靠性评估流程；其次，考虑结构时变退化的影响，基于长期位移监测数据，并结合时域优化技术，建立了大跨箱梁桥有限元模型动态验证方法，为结构状态评定提供了基准模型；然后，依据试验研究，深入探讨了预应力长期损失的主要影响因素，基于按龄期调整的有效模量法，建立了考虑混凝土静徐变、收缩、应力松弛相互作用和普通钢筋影响的预应力长期损失计算模型，实现了长期损失的精确预测，完善了桥梁结构设计理论；依据速率型徐变定律，在DIANA软件平台，构建了考虑循环徐变、静徐变等多因素耦合效应的统一本构模型，实现了大跨箱梁桥时变性能的精细化模拟；最后，基于随机有限元法，并结合自适应重要抽样技术，建立了考虑循环徐变等多重劣化因素耦合效应的大跨箱梁桥时变可靠度高效算法，揭示了多重劣化因素耦合作用下大跨箱梁桥可靠度演化规律。本项目研究成果为大跨箱梁桥的状态评估、性能提升和优化设计提供了技术支撑，具有重要的理论指导价值和实践意义，推广潜力极大。