基于FOSM法的预应力钢桁架系统可靠性分析

基于一次二阶矩法(FOSM)建立了索张拉预应力钢桁架任意单元失效模式可靠性指标的计算模型,并分别根据点估计法和窄界限法得到了整体结构失效概率的计算公式,随机内力统计特性-均值和标准差则根据随机摄动理论确定.该计算模型中的基本随机参数包括任意折线索单元和桁架单元的截面面积 (或综合刚度) 、张拉钢索的预拉力、外荷载及弹性约束刚度等.利用本文计算模型编写的计算程序对工程中普遍采用的结构形式进行了可靠性分析,并对影响结果的有关参数进行了讨论,为索张拉预应力钢结构整体可靠性设计奠定了一定的基础.分析表明,窄限法得到的整体可靠性指标与点估计法(PNET)所确定的基本一致, 这是因为本文计算模型中各失效模式间的相关系数较小之故.此外,随机变量的相关性对预应力钢结构不同阶段可靠性指标有不同的影响,其中加载阶段影响更大.

Reliability analysis of prestressed steel structural system on FOSM

The method of First-Order Second-Moment is used to establish the computational model of reliability index of each element of prestressed steel trusses,and the reliability index of the structural system is further obtained with the method of PNET and Narrow Bounds.The random perturbation method is used to obtain the computational model of statistical characteristics of random internal forces of the structures with elastic restraint,in which the random parameters of areas of cross sections of all the elements,areas of cables, prestress of cables,external forces and stiffness of elastic restraint are considered.Finally,some computational examples of prestressed steel trusses which are common used in engineering are put forward and the results are discussed to obtain some useful conclusions,which can be used as basis for design of the prestressed steel structural system.The reliability index of the structures obtained with the method of narrow bounds are well identified with the results given by the methods of PNET,which is related to the fact that relevant coefficients of failure models with each other are quite small.It is also concluded that relativity of random variables has different effect on reliability index of the structure in different stages,and the effect in loading stage is much greater.