中文摘要：

箱梁容易在支座、1/4跨及跨中位置出现裂缝,箱梁开裂病害与箱梁过量下挠相互耦合,其作用机理较为复杂,评估箱梁过量下挠的难点在于箱梁裂后的刚度分布特性研究。为了有效评估箱梁裂后刚度,制作了大比例尺预应力混凝土连续箱梁模型,开展了反复荷载作用下的箱梁破坏性试验,分别采用两种方法开展了箱梁裂后刚度分布特性研究。第一种方法,结合试验数据,基于Levenberg-Marquardt优化算法,对已测试得到的不同开裂程度下的挠度进行刚度分布反演;第二种方法,基于模型试验测试的荷载挠度曲线直接建立刚度折减评估参数,对开裂后箱梁的刚度损伤分布进行统计分析。对比分析了两种方法计算得到的箱梁裂后刚度纵向分布特征,验证了评估结果的有效性。研究结果表明：箱梁裂后开裂区域的刚度折减系数以加载位置为参考点,其余部位的刚度损伤沿箱梁纵向呈线性分布。提出了箱梁裂后刚度损伤计算方法。该研究可对开裂后箱梁的服役性能评估提供了理论参考。

英文摘要：

Cracks normally appear at supports, 1/4 span and mid span of box girders. Box girder cracking was coupled with excessive deflection of box girders, and its mechanism was complex.The difficulty to assess excessive deflection of box girder was it＇s stiffness distribution characteristics after cracking. In order to evaluate the box girder cracking stiffness, a large scale model of a continuous prestressed concrete box girder is made, destructive tests under repeated loading are carried out on the model. Two methods are used to research stiffness distribution characteristics of the cracking box girder. In the first method, combined with experimental data, stiffness distribution inversion of deflection at different crack degree is computed based on the Levenberg-Marquardt optimization algorithm. In the second method, the stiffness reduction evaluation parameter is directly set based on the load-deflection curve from the model test. Statistical analysis on stiffness damage distribution of box girder after cracking is done. Effectiveness of evaluation results is verified through comparing and analyzing stiffness longitudinal distribution characteristics of box girder after cracking obtained by the two methods. The results show that： the loading position is a reference point of stiffness reduction factor in box girder cracking zone. Stiffness damages on other positions are linear distribution along longitudinal direction of the box girder. The cracking box girders＇ stiffness damage calculation method is proposed. This study can provide theoretical reference for service performance evaluation of prestressed concrete box girders.