During the past decade, the progressive collapse of structures has received growing attention, and the study of member importance is a key step for investigating the progressive collapse resistance. However, traditional methods for evaluating the member importance usually employ a single indicator, and when multiple indicators are involved, different indicators may generate different member rankings. Moreover, the truss string structure is a multiple super-stationary structure with many members, and the current studies mainly focus on cable failure, which does not mean that other members are not important. In this study, the initial selection of important members is first performed based on concept evaluation, and then, the alternate path method is used to analyze the progressive collapse resistance of truss string structures; the slope degradation coefficient γ of incremental dynamic analysis curve, load capacity degradation coefficient β, and nested load capacity degradation coefficient β′ are introduced; and the sensitivity coefficient SI_j and fragility coefficient VI_i are defined with axial force as the structural response. Based on the above five indicators, two cases are conducted to evaluate the member importance. The analysis results show that the cable and the bottom chord member at the support are evaluated as the first-level important members. Through the analysis of different indicators, it is found that the regularity of the coefficient of each member is inconsistent for different indicators. The results could be one-sided if the important members were evaluated by a single indicator only. In addition, the second-level important members of truss string structures are evaluated by multi-indicator analysis. Finally, the nominal progressive collapse resistance of truss string structures is given based on the importance coefficient of the first- and second-level important members.

中文翻译：

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桁架弦结构重要构件的多指标评价方法

在过去的十年中，结构的渐进倒塌受到越来越多的关注，而杆件重要性的研究是研究渐进倒塌抗力的关键一步。然而，传统的成员重要性评价方法通常采用单一指标，当涉及多个指标时，不同的指标可能会产生不同的成员排名。而且，桁架弦结构是一种具有多个杆件的多重超固定结构，目前的研究主要集中在拉索失效方面，这并不意味着其他杆件不重要。本研究首先基于概念评价对重要构件进行初步选择，然后采用交替路径法对桁架弦结构的渐进倒塌抗力进行分析；引入了增量动态分析曲线的斜率退化系数γ、承载能力退化系数β、嵌套承载能力退化系数β ′；以轴力为结构响应定义灵敏度系数SI _j和脆性系数VI _i 。基于以上五个指标，通过两个案例来评估会员重要性。分析结果表明，锚索和支座下弦杆被评定为一级重要杆件。通过对不同指标的分析，发现各成员系数对于不同指标的规律性不一致。如果仅用单一指标来评价重要成员，结果可能是片面的。此外，还通过多指标分析对桁架弦结构的二级重要构件进行了评价。最后根据一级、二级重要构件的重要性系数给出了桁架弦结构的名义连续倒塌抗力。