钢筋混凝土梁的时变可靠度实用分析方法

考虑服役期内的抗力退化和评估使用年限缩短,采用实用方法分析钢筋混凝土梁受弯承载力的时变可靠度.首先,考察了不考虑抗力退化时结构累积失效概率的发展规律,证明“累积失效概率与服役年数成正比”的规律总体成立.其次,以二次曲线近似表达混凝土梁受弯承载力的退化过程,比较了不同抗力退化率下结构累积失效概率及可靠指标的发展过程,同时分析了等时段内结构失效概率及可靠指标的变化,并发现如下规律:抗力退化不严重时,分段可靠度的乘积接近设计或评估使用年限内的可靠度,但抗力退化严重时这个规律不存在.最后,对采用抗力退化系数-荷载效应折减系数比较的近似法与可靠度法的计算结果进行了比较,结果表明近似法总体上更能反映抗力退化与使用年限缩短引起的结构时变可靠度变化规律,便于工程应用.

A Practical Analysis Method for Time-Variant Reliability of Reinforced Concrete Beam

The time-variant reliability of bending capacity of a reinforced concrete beam was analyzed by using a practical analysis method considering resistance degradation in service life and shortening of assessed working life.Firstly,the development law was studied for the structure cumulative failure probability without consideration of resistance degradation,and the general rule was proved that the cumulative failure probability was proportional to the number of service years.Secondly,the bending capacity degradation process of concrete beam was expressed approximately by a quadratic curve.The development process of structure cumulative failure probability and reliability index were compared under the different conditions of resistance degradation ratio.The change of structure failure probability and reliability index in the equal time duration were analyzed.A law was found that when the resistance degradation was not very serious,the product of reliabilities of each time duration was close to the reliability within the design working life or assessed working life.When the resistance degradation was significant,the above law did not exist.Finally,calculation results of the approximate method comparing the resistance degradation coefficient with the load effect discount coefficientwere compared with that of the reliability method.It was shown that the approximate method could reflect the time-variant reliability variation law of the structure caused by the resistance degradation and the shortening of assessed working life.The approximate method was convenient for engineering application.