基于可靠指标的桥梁结构稳定安全系数研究

Study on Stability Safety Factor of Bridge Structure Based upon Reliability Index

桥梁相关规范规定,结构的第一类稳定安全系数不应小于4,但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则值得研究。以钢筋混凝土受压构件为例,分别进行弹性和弹塑性稳定计算,取第一类稳定安全系数等于4,采用一次可靠度方法FORM得出第一类弹性失稳时的可靠指标,利用计算该可靠指标时的荷载效应和弹塑性临界荷载计算第二类弹塑性失稳时的可靠指标。结果表明:某些情况下,当第一类稳定安全系数取4时并不足以保证结构发生第二类失稳时的可靠指标达到目标可靠指标。文中还讨论了结构参数变化对结构第一类和第二类失稳时可靠指标及稳定安全系数的影响,得出第二类稳定安全系数和可靠指标的关系,并给出第二类稳定安全系数的取值建议。

According to the terms of relevant bridge specifications , the first kind of stability safety factor should not be less than four .But when it is chosen to be four ,it is worth studying whether it is guaranteed that the reliability index of the structure under the instability of the second kind reaches the target reliability index . In this paper , taking the reinforced concrete compressive member as an example , the linear elastic stability and the elastic-plastic stability of it were calculated . Supposing the first stability safety factor was four , FORM was employed to calculate the reliability index under the instability of the first kind . Then the load effect used in the instability of the first kind and the collapse load were adopted to calculate the reliability index under the instability of the second kind . T he result show s that the reliability index under the instability of the second kind can not be guaranteed to achieve the target reliability index under certain situations w hen the first kind of stability safety factor is chosen to be four . In this paper , the influence of variations of structural parameters on the reliability index under the instability of the first kind and the instability of the second kind and on the stabil-ity safety factor was discussed so that the relationship between the second stability safety factor and the reliabil-ity index was found .Suggestions were also given on determining the value of the second kind of stability safety factor .