装配式PC箱梁刚度退化及识别的足尺试验

为了明确装配式预应力混凝土（PC）梁刚度在损伤状态下的退化规律，针对3片30 m预应力混凝土箱梁开展了足尺模型试验研究。首先，建立了损伤梁的结构静动刚度识别模型，基于跨中挠度提出了结构等代静刚度计算式，基于自振频率提出了结构等代动刚度的计算式；其次，对足尺箱梁进行了多工况的静力逐级加载和动力交替试验，分析了箱梁裂缝、挠度、频率等特征参数随荷载的演化规律，研究了损伤状态对箱梁特征参数的影响；再次，通过有限元模型修正给出了箱梁动刚度衰减系数，研究了结构静动刚度随损伤状态的衰减规律，分析了静动刚度差异的原因；最后，建立了结构静动刚度衰减系数和裂缝特征参数之间的经验回归式，并与现有研究成果进行了对比。结果表明：初始损伤状况对箱梁受荷后的裂缝统计分布特征参数有一定影响；箱梁开裂后在相同荷载下的结构等代静、动刚度衰减程度并不相同，其中最终的静刚度衰减系数为0.30，最终的动刚度衰减系数为0.80；足尺梁与室内缩尺模型梁的静刚度衰减系数并不相同。所提出的静、动刚度衰减公式较为简洁，可用于实际损伤箱梁的结构性能评估。

Full-scale Experiment on Stiffness Degradation and Identification of Prestressed Concrete Box Girders

To study stiffness degradation under damaged conditions for prestressed concrete (PC) girders, a full-scale model test was conducted on three 30 m PC box girders. First, static and dynamic stiffness identification models of damaged beams were developed. The equivalent static stiffness was calculated based on beam deflections in the mid-section, and the equivalent dynamic stiffness was calculated based on its natural frequencies. Second, full-scale girders were loaded incrementally, and static and dynamic tests were conducted alternatively. The development of cracks, deflections, and frequencies of the experimental girders under different loads were then studied, and the effects of damage conditions on these parameters were analyzed. Third, the reduction coefficients of dynamic stiffness were derived using the finite element model updating method, and the relationship between static and dynamic stiffness with the damage conditions was analyzed. The difference between the static and dynamic stiffness was then explored. Finally, the regression formula of the reduction coefficients of the static and dynamic stiffness with crack feature parameters was established and compared with previous studies. The results show that the initial damage condition of the girder has an effect on the statistical distribution of the crack features. It also illustrates that the degradation of equivalent static and dynamic stiffness of the girder is not consistent, where the final reduction coefficients of static and dynamic stiffness are 0.30 and 0.80, respectively. The reduction coefficient of static stiffness between the full-scale and scale-down model tests is different. The study presents a simple method for the reduction coefficients of static and dynamic stiffness to assess damaged PC box girders in practical engineering.