预应力混凝土箱梁损伤后剩余承载力计算及变化规律研究

目前对在役桥梁进行技术状况评定时，往往需采用荷载试验的方法来反映桥梁结构实际损伤所产生的性能退化。然而，荷载试验方法存在费用高、耗时长等问题，进行荷载试验代价巨大，且对于存在损伤的结构具有一定的风险。因此，基于对一新建跨径30 m预制预应力混凝土箱梁进行的足尺模型试验结果，构造定义了2种不同的刚度损伤折减系数，结合规范给出的开裂构件抗弯刚度计算公式，提出基于刚度损伤折减系数计算构件实际剩余承载力的计算公式。结果表明：2种方法定义得到的抗弯刚度折减系数的变化趋势基本一致，箱梁在出现损伤后的刚度折减效应明显，从箱梁出现开裂损伤到承载能力极限状态刚度折减约40%，相邻两截面的刚度折减可近似呈线性分布；基于刚度损伤折减系数计算的剩余承载力与试验值的偏差都在5%以下；结合刚度折减系数沿箱梁纵向的分布规律，可计算得出在跨中截面出现损伤后，沿箱梁纵向各截面实际剩余承载力的分布规律。提出的基于刚度损伤折减系数计算实际剩余承载力的方法，可通过结构外观检查结果实现对带有损伤的预应力混凝土箱梁实际剩余承载力的准确计算，该方法简便可行、费用低廉，同时也可为出现损伤的在役桥梁技术状况评定及剩余承载力计算提供一定的借鉴。

Research on Residual Bearing Capacity Calculation Method and Changing Law of Damaged Prestressed Concrete Box Girder

At present, the load test method is frequently used to determine the performance degradation caused by actual damage of bridge structures in the technical condition assessment of bridges in service. However, this method is often costly and time-consuming, and there are several risks associated with the use of load tests on damaged structures. In this study, according to the ultimate bearing capacity test of a precast pre-stressed concrete box girder in 30 m span full-scale model results, the stiffness damage reduction coefficient of the test beam is given by two methods. Combining the defined stiffness damage reduction coefficient with the formula for calculating the flexural stiffness of cracked members given in the specification, the formula for calculating the residual bearing capacity of cracked members based on the stiffness damage reduction coefficient was obtained. The results show that the variation trend of the stiffness reduction coefficient calculated by the two methods is similar, and the stiffness reduction effect of the box girder after damage is obvious; the reduction in the stiffness is approximately 40% from the cracking to the ultimate state of the bearing capacity. The stiffness reduction of two adjacent sections can be approximately and linearly distributed, and the calculation results reveal that the deviation between the calculated bearing capacity and the test value of the two methods is less than 5%. Combined with the distribution law of the stiffness reduction coefficient along the longitudinal direction of the box girder, the distribution law of the residual bearing capacity along the longitudinal direction of the box girder can be calculated. As shown in this study, the residual bearing capacity of a prestressed concrete box girder with damage can be calculated accurately according to the degree of structural damage. This method is simple and inexpensive, and can be used to evaluate the condition of damaged bridges and provide a reference for calculating the ultimate bearing capacity.