基于可靠指标的稳定安全系数探讨

The stability safety factor calibration based on the reliability index

桥梁结构当第一类稳定安全系数取4时,能否保证结构在更可能出现的第二类失稳发生时的可靠指标达到目标可靠指标值得研究。对单层单跨刚架桥分别进行了第一类和第二类稳定计算,以第一类稳定计算得到的临界荷载,取第一类稳定安全系数为4,采用一次可靠度方法编制程序得出可靠指标。进而采用第一类稳定可靠指标计算时的荷载效应和第二类临界荷载来计算第二类可靠指标。根据可靠指标探讨结构稳定安全系数取值的合理性。在此基础上,对两类稳定临界荷载进行了参数分析,研究临界荷载的变化对可靠指标的影响。结果表明:稳定分析应区分失稳状态,第一类稳定安全系数取4,但当结构发生第二类失稳时,有些情况下不足以保证可靠指标达到目标可靠指标。

When the bridge structure stability safety factor of the first type is 4,the research that whether the structure reliability index will reach target reliability index under the more-likely-to-happen collapse situation of the second type is necessary.The stability calculations of the first and the second type are made respectively for single layer and single span rigid frame bridge.Based on the critical load obtained from the stability calculation of the first type,the stability safety factor of the first type is taken as 4,and the first order reliability method is used to program and calculate the reliability index.Then,the load effect under the stability reliability index calculation of the first type and the critical load of the second type are employed to calculate the reliability index of the second type.The evaluation of structure stability safety factor is discussed according to reliability index.Based on the discussion above,parameter analysis of the stable critical loads of two types is made,and the influence of critical load change on reliability index is researched.The result shows that stability analysis should identify collapse state;when the stability safety index of the first type is 4,and the structure has the collapse of the second type,the reliability index cannot ensure to reach the target reliability index under some situations.