概率性能基础的使用寿命设计

氯盐环境下钢筋混凝土结构过早被破坏,很多因素影响混凝土的使用寿命,这些因素随着环境和时间而变化,是随机变量,应采用数理统计方法处理或采用荷载抗力分项系数法设计,在使用寿命设计中,输入一个代表值进行计算,如果这个数值是该变量的平均值,计算结果的使用寿命只有50%的保证率。如果按95%的分位数取扩散系数值,各影响因素(包括扩散系数)用分项系数来反映可靠指标,则可提高使用寿命保证率到95%,但目前使用寿命设计具有不确定性,在结构使用期间应对结构性能进行跟踪维护,对有关性能进行定期检验,据以进行使用寿命再设计,也许进行多次再设计,以确保结构有设计要求较长的使用寿命。

Probabilistic Performance Based Service Life Design

Reinforced concrete structures exposed to chloride develops premature failure and there are many factors influencing the service life of concrete.These factors vary with time and are random variables.Methods of mathematical statistics should be used to handle these factors or method of load resistance sub-parameters should be used to make calculations.In the service life designs,a representative value is input to make the calculations.If the value is a mean value of the variable,the calculated service life is only 50% of the assurance factor.If the diffusion coefficient is chosen from the quantile of 95% and the influencing factors(including the diffusion coefficient)are chosen as the sub parameters to reflect the reliability indexes,the assurance factor of the service life can be increased to 95%.But,the current service life designs are of uncertainty.As a result,the performance of a structure should be monitored and maintained during the service of the structure and periodic measurements shall be made of its relevant performance,on the basis of which,the service life should be redesigned and may be redesigned a number of times to ensure that the structure will have a longer design life as required.