分析了目前既有结构时变可靠度计算理论和现行规范计算公式,考虑混凝土损伤和钢筋锈蚀以及材料强度随时间劣化的情况,建立了既有钢筋混凝土梁(单筋矩形截面、双筋矩形截面和T形截面)的时变抗力计算模型,给出了既有钢筋混凝土梁的时变可靠度指标,并通过工程实例对既有钢筋混凝土梁进行了加固前计算分析。结果表明:实例结构动态可靠度指标为1.56,承载能力属于d级,这与现行可靠性鉴定标准的评级相吻合,因此,计算模型合理可靠。 The existing time-varying reliability theory and current standard calculation formula are analyzed. Considering the damage of concrete and corrosion of reinforcing steel and the deterioration of material strength with time, the existing reinforced concrete beams (single-bar rectangular section, double-bar rectangular section And T-shaped cross-section), the time-dependent reliability index of the existing RC beams is given, and the existing RC beams are calculated and analyzed before and after reinforcement by engineering examples. The results show that the dynamic reliability index of the example structure is 1.56 and the carrying capacity belongs to d level, which agrees with the current rating of reliability appraisal standard. Therefore, the calculation model is reasonable and reliable.