中文摘要：

在平截面假定不成立的前提下,以钢筋混凝土Π梁为研究对象,探讨不同锈蚀率的钢筋混凝土Π梁极限抗弯承载力的变化规律,通过构造新的几何协调条件,提出既有钢筋混凝土Π梁的计算受压区高度随锈蚀率变化的计算公式,进而推导出既有钢筋混凝土Π梁的正截面抗弯承载力计算公式。在此基础上,结合服役约40 a的实桥试验材质检测参数及破坏荷载对承载力公式进行验证。研究结果表明：由本文推导的承载力公式所得计算结果与试验结果较吻合,说明所提出的既有钢筋混凝土Π梁的极限抗弯承载力计算方法正确、有效,可应用于指导工程实践。

英文摘要：

On the basis of the incorrectness of the plane-section assumption,reinforced concrete Π beams was taken as the research object and the variation law of the bearing capacity of beams was established with different corrosion rates.By constructing the new deformation compatibility,the calculation formula of the compression depth of existing reinforced concrete Π beams varying with corrosion rate was presented,and the calculation formula of normal section capacity of existing reinforced concrete Π beams was derivered.Based on these analyses,the presented formula verifies the calculation formula of the flexural capacity using the experimental data for perimeters of material quality and damage loads obtained from a real bridge that served for about 40 years.The results indicate that the computational results of the calculation formula are in good agreement with the experimental results,which shows that the calculation formula of flexural capacity is effective and can be applied in engineering practice.