Multi-indicator evaluation method of important members of truss string structures

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 gamma of incremental dynamic analysis curve, load capacity degradation coefficient beta, and nested load capacity degradation coefficient beta ' are introduced; and the sensitivity coefficient SIj and fragility coefficient VIi 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.