Growing attention has been focused on the design of structures resisting progressive collapse during the past decade. The cables of prestressed large-span space structures may fracture in complex service environments, triggering a progressive collapse of the structure. The objective of this study is to elucidate the failure mechanisms and modes of truss string structure (TSS) with alternate cables (TSSACs) under the breakage of the lower cable, to compare the effects of different alternate cable scenarios on the progressive collapse resistance of TSSs, so as to provide strategic guidelines and data support for the design and application of TSSs, and to establish a technique for the improvement of the anti-progressive collapse capacity of TSSACs. It is found that the anti-progressive collapse failure mechanisms and failure modes of different alternate cable scenarios are significantly different. The failure modes of TSSACs under mid-span cable failure are plastic hinge occurring on the right side of the 1/3 span with buckling of the strut in the mid-span; plastic hinge occurring in the mid-span with buckling of the struts on both sides; plastic hinge occurring on the left side of the 1/3 span; and plastic hinge occurring in the mid-span, respectively. Moreover, the cable failure location can also affect the failure mode of TSSACs. The arrangement of alternate cables can remarkably improve the resistance of normal TSSs to progressive collapse, with the most significant improvement of 44.4 % under mid-span cable failure. Whereas, the progressive collapse resistance increases by 123.6 % when the cable fails at the support. In addition, it is noticed that there exists an obvious turning point in the horizontal displacement time-history curves of the support, which signals the beginning of the progressive collapse of the structure. Furthermore, parametric analyses show that strain rate parameters, cable failure time, and dynamic increase factor have a significant effect on the anti-progressive collapse performance of TSSACs. The cable prestressing has a minor effect on the progressive collapse resistance. The effects of horizontal support stiffness on the progressive collapse-resistant performance of TSSACs are also discussed. The results show that increasing the support stiffness has a certain enhancement effect on the resistance against progressive collapse, and the larger the support stiffness is, the more obvious the enhancement effect is. It is also found that increasing the support stiffness can effectively reduce the mid-span deformation before the formation of the plastic hinge, as well as reducing the maximum displacement of the horizontal support. However, it is not favorable to the large-span space structure that increasing the support stiffness greatly raises the horizontal reaction force. Therefore, while strengthening the progressive collapse resistance of TSSs, it is inevitable to consider the adverse effects of excessive support stiffness during the structural design process.

中文翻译：

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交替索桁架柱结构的抗渐进式抗倒塌及破坏机理研究


在过去十年中，人们越来越关注抵抗渐进式倒塌的结构设计。预应力大跨度空间结构的索在复杂的服役环境中可能会断裂，从而引发结构的逐渐倒塌。本研究旨在阐明下部索断裂下交替索 （TSSAC） 的桁架柱结构 （TSS） 的失效机制和模式，比较不同交替索情景对 TSS 的渐进式抗倒塌性能的影响，以期为 TSS 的设计与应用提供战略指导和数据支持。 并建立一种提高 TSSAC 抗进行性崩溃能力的技术。研究发现，不同交替索情景的抗渐进式塌陷失效机制和失效模式存在显著差异。中跨索破坏下 TSSAC 的破坏模式为 1/3 跨右侧出现塑性铰链，跨中支柱屈曲;塑料铰链发生在跨中，两侧支柱屈曲;塑性铰链出现在 1/3 跨度的左侧;和塑性铰链分别出现在跨中。此外，电缆故障位置也会影响 TSSAC 的故障模式。交替电缆的布置可以显著提高正常 TSS 对逐渐塌陷的抵抗力，在中跨电缆故障下最显着的改进为 44.4 %。然而，当电缆在支撑处失效时，渐进式抗塌陷性增加了 123.6%。 此外，值得注意的是，支撑的水平位移时程曲线中存在一个明显的转折点，这标志着结构逐渐崩溃的开始。此外，参数分析表明，应变速率参数、电缆失效时间和动态增加因子对 TSSACs 的抗渐进式塌陷性能有显著影响。索预应力对渐进式抗塌性的影响很小。还讨论了水平支撑刚度对 TSSAC 的渐进式抗塌陷性能的影响。结果表明：提高支座刚度对抵抗进行性塌陷具有一定的增强作用，且支座刚度越大，增强效果越明显。研究还发现，提高支护刚度可以有效减少塑性铰形成之前的跨中变形，以及减小水平支护的最大位移。然而，对于大跨度空间结构来说，增加支护刚度会大大提高水平反作用力，这并不利于该结构。因此，在加强TSSs的抗渐进式抗倒塌性能的同时，在结构设计过程中不可避免地要考虑过大支护刚度的不利影响。