冻融损伤混凝土的弯曲疲劳寿命可靠性分析

Flexural fatigue-life reliability of frost-damaged concrete

为了研究冻融损伤效应对混凝土弯曲疲劳寿命的影响,通过三点弯曲疲劳试验研究经快速冻融法水冻至不同损伤程度的混凝土小梁疲劳寿命;并用两参数威布尔分布函数对弯曲疲劳寿命试验数据进行拟合和检验;对混凝土弯曲疲劳寿命的可靠性进行分析并建立具有不同可靠性概率的P-S-N曲线.研究结果表明:混凝土的静弯曲强度、疲劳强度和疲劳寿命都随着冻融循环(FTC)次数的增加而急剧减小.K-S检验结果表明:混凝土弯曲疲劳寿命能很好地服从威布尔分布;利用矩估计法获得的威布尔分布参数的混凝土弯曲疲劳寿命的分散性随应力水平的增大而减小,随冻融作用次数的增加而增加.可靠性分析结果表明:混凝土弯曲疲劳寿命的可靠性概率随着冻融次数的增加而有所降低,对混凝土弯曲疲劳寿命(强度)进行设计和验算时应适当增大受冻融损伤混凝土的可靠性概率(安全系数).

The three-point bending tests were conducted on concrete beam specimens which were first frostdamaged by the rapid frozen-thaw method in order to investigate the effect of frost-damaged on flexural fatigue life of concrete.A two-parameter Weibull distribution model was introduced to describe the experimental flexural fatigue life and the reliability probability analysis was carried out to calculate the theoretical flexural fatigue life for the frost-damaged concrete.Based on the experimental and theoretical studies,the relationship of the fatigue life-fatigue strength and the P-S-N curve was obtained.It is shown that static flexural strength,flexural fatigue strength and life significant decrease as the number of freezethaw cycles(FTC)increase.The tested results of the K-S test indicate that the two-parameter Weibull distribution function can appropriately describe the probability distribution of flexural fatigue life.Results of the estimated shape parameter of the Weibull distribution by the method of moments show that the scatter of the flexural fatigue life increases with the increase of the number of FTC.Reliability analysis results indicate that the reliability probability(safety factor)of the flexural fatigue life for the frost-damaged concrete decrease as the number of FTC increase.For the concrete structure service in cold climate regions,it is necessary to increase the value of safety factor of the flexural fatigue life(strength)to resist the fatigue loading.