考虑氯离子侵蚀与混凝土碳化的公路桥梁时变可靠度分析

基于国内外对氯离子侵蚀和混凝土碳化环境下钢筋锈蚀速率的最新研究成果,建立了混凝土构件在氯离子侵蚀下考虑坑蚀和在混凝土碳化下考虑平均锈蚀的弯曲抗力退化模型,用Monte Carlo方法和统计回归法编制了退化钢筋混凝土构件及系统的时变可靠度计算程序。以北京地区一座公路桥为算例,结果表明:在氯离子侵蚀下考虑坑蚀的桥梁承载能力时变可靠度在30年左右即下降到设计目标可靠度,在混凝土碳化下考虑平均锈蚀的桥梁承载能力时变可靠度在50年左右即下降到设计目标可靠度,从而需要补强,这表明考虑主筋锈蚀后我国钢筋混凝土公路桥一般达不到100年设计使用期;对因主筋锈蚀导致混凝土保护层胀裂而言,构件达到抗裂正常使用极限状态远远早于达到承载能力极限状态,建议将混凝土保护层开裂时间作为桥梁检查/维修参考点。

ANALYSIS OF TIME-DEPENDENT RELIABILITY OF RC HIGHWAY BRIDGES CONSIDERING CHLORIDE ATTACK AND CONCRETE CARBONATION

Based on the results of other researchers on the corrosion rate of tensile reinforcement steel, moment resistance deterioration models of reinforced concrete girder bridges due to steel corrosion induced by chloride attack or concrete carbonation are developed with pitting corrosion being considered for chloride attack and average corrosion being considered for concrete carbonation. A computer program for time-dependent reliability assessment of highway concrete bridges based on Monte Carlo method and statistic regression is also developed. A concrete girder bridge in Beijing area is taken as an example. The results show that the ultimate limit state reliability of the bridge due to chloride attack reduces to the design target reliability at the 30th year or so and the reliability due to concrete carbonation to the value at the 50th year or so. Therefore, the bridge can not work through the presumed working life of 100 years without major repair. The results also show that cracking time of concrete cover induced by corrosion of tensile reinforcement is much earlier than the time when the ultimate limit state reliability reduces to the target value. This is important for bridge inspection/repair schedule.