公轨两用双层连续钢桁梁桥体系可靠度分析

System Reliability Analysis of Rail-road Double-deck Continuous Steel Truss Bridge

为提高大跨度连续钢桁梁桥静力体系可靠度计算效率与准确度,基于改进向量投影响应面法(IVPRSM)建立了体系可靠度计算模型。通过优化向量投影响应面法的取样过程,实现钢桁梁构件功能函数的高效拟合和验算点的精确捕捉,形成构件可靠指标的高效改进算法;应用修正的β分支约界法识别失效历程中的候选失效单元,采用IVPRSM计算随结构拓扑模型改变而更新变化的构件可靠指标,搜寻桁梁结构主要失效模式,建立桁梁桥失效树;在确定各失效模式等效线性功能函数和失效模式相关系数的基础上,利用改进的微分等价递归算法实现结构体系可靠度计算。通过3个数值算例的可靠度分析,验证IVPRSM的正确性和有效性;以主跨300 m的双层连续钢桁梁桥为工程实例,采用提出的体系可靠度计算模型,分析失效历程各阶段桁梁结构关键构件可靠指标的演化规律。研究结果表明:IVPRSM的计算效率和计算精度均优于传统方法;承载能力极限状态下,各类关键构件的可靠指标最小值为4.1~4.8,桁梁主跨中支点处下弦、300 m主跨1/4处上弦与腹杆、主跨跨中处加劲竖杆失效风险大;搜寻获得承载能力极限状态主要失效模式20个,计算该双层桁梁桥体系可靠指标为4.6。建立的基于IVPRSM的静力体系可靠度分析方法可支撑双层钢桁梁桥体系可靠性设计。

A system reliability analysis model is developed using an improved vector projection response surface method(IVPRSM)to enhance the efficiency and accuracy of calculating the static system dependability of long-span continuous steel-truss bridges.A novel approach was developed to enhance the efficiency of computing the component dependability index by optimizing the sampling process of the vector projection response surface technique.The limit state functions of steel truss bridge components can be effectively rebuilt,the design points can be promptly searched,and the failure probability of the components can be evaluated using the IVPRSM.The candidate failure components can be screened using theβ-unzipping method.Considering the structural topology model was modified by assuming failure in the potential failure elements,the reliability indices of the remaining components were calculated using IVPRSM.Therefore,identifying the primary failure modes of steel-truss bridges and constructing a fault tree is possible.The structural system reliability index was determined using the differential equivalent recursion technique,which relied on the equivalent linear functions of the failure modes and the correlation coefficients between the failure modes.The efficacy and precision of the IVPRSM were confirmed through a reliability study of three numerical arithmetic cases.Considering a double-deck continuous steel truss bridge with a main span of 300 m as an engineering example,the proposed system reliability analysis method was used to calculate the reliability indices of the key components of the steel truss bridge in each failure stage.The study findings demonstrate that IVPRSM exhibits superior computational efficiency and accuracy compared with conventional approaches.At the ultimate limit condition of the load-carrying capacity,the reliability index for all types of critical members ranges from 4.1 to 4.8.The lower chord at the pivot of the main span of the truss girder,the upper chord and web member at approximately 1/4 of the main span(300 m),and the strengthened vertical bar in the center of the main span pose a significant danger of failure.Consequently,twenty primary failure modes affecting the load-carrying capability of the steel truss bridge were identified,resulting in a system dependability index of 4.6.This study proposes an IVPRSM-based reliability method for the static systems of continuous steel truss bridges.This algorithm may assist in designing continuous steel truss bridges by considering system reliability.