考虑偏心距随机特性的矩形和箱形截面混凝土拱桥可靠度分析

Analysis of Reliability of Rectangular Sectional and Box Sectional Concrete Arch Bridges Based on Random Eccentricity

为研究偏心距随机特性对结构可靠性的影响,以自重荷载和车辆荷载组合作用下的混凝土矩形截面拱桥和混凝土箱形截面拱桥为研究对象,分析可靠指标的变化规律。根据《公路圬工桥涵设计规范》和《公路桥梁结构可靠度与概率极限状态设计手册》建立拱桥关键截面的失效方程。然后依据已有的永久荷载、汽车荷载和混凝土强度的概率模型,分析偏心距设计值在对应情形下具有的保证概率。采用Monte Carlo法,求解得到不同参数情形下两类截面混凝土拱桥的可靠指标。分析结果表明:当车辆荷载与永久荷载产生的轴压力的比值较大而两者产生的弯矩的比值较小时,两类截面混凝土拱桥在考虑偏心距随机特性后均会出现可靠指标低于规范校核结果的情形;在偏心距设计值较小时,箱形截面混凝土拱桥可靠指标随荷载效应比值变化的幅度比矩形截面拱桥要小。

To study the influence of random natures of eccentricity on structural reliability, taking concrete arch bridges with rectangular section and box section under the combined effects of dead load and vehicle load for examples, the variation regularities of reliability indexes are analyzed. According to the Code for Design of Highway Masonry Bridges and Culverts and the Manual for Reliability and Probability Limit State Design of Highway Bridges, the failure functions of critical sections of arch bridge are established. Based on the current probability models of dead load, vehicle load and concrete strength, the guaranteeing probabilities of the designed eccentricity are analyzed correspondingly. Using Monte Carlo method, the reliability indexes of concrete arch bridges with the 2 sections with different parameters are obtained. The result shows that （ 1 ） when the ratio of axial compression forces generated by vehicle load to that generated by dead load is larger and the corresponding ratio of bending moments is smaller, the reliability indexes of concrete arch bridges with the 2 sections considering random eccentricity are lower than those given in the codes; （2） when the designed value of eccentricity is smaller, the variation magnitude of reliability index of concrete arch bridges with box section varying with ratio of load effects is smaller than that of concrete arch bridge with rectangular section.