网架结构屋盖在体育场馆、剧院等公共建筑和工业厂房中应用广泛。然而，近年来，网架结构屋盖倒塌事故时有发生，因此确保整体结构具备良好的抗连续倒塌能力尤为重要。本文以一主体为钢筋混凝土框架结构，带有网架屋盖体系的实际工程为背景，建立三维有限元模型，采用备用荷载路径法，研究不同位置构件初始失效，剩余结构在竖向荷载作用下的抗连续倒塌能力，并计算采用非线性静力分析方法时的动力放大系数；另探讨该结构在地震作用下的抗连续倒塌能力，分析杆件加固对结构抗连续倒塌性能的影响。主要研究内容及结论如下：

建立结构整体弹塑性分析模型，基于应力敏感性分析计算杆件的敏感性指标和重要性系数，确定结构的关键杆件，结果表明，结构的关键杆件为跨中及支座处的上弦杆，跨中下弦杆和支座处的腹杆。

采用备用荷载路径法，拆除网架结构不同位置的关键杆件和下部框架柱，对剩余结构进行抗连续倒塌分析。结果表明，单根跨中上弦杆和短边中柱的初始失效会引起网架结构的连续倒塌破坏，单根下弦杆、支座处上弦杆或腹杆以及角柱和长边中柱的初始破坏不会造成剩余结构的连续倒塌。双根跨中下弦杆或支座腹杆的连续失效会使结构发生连续性的倒塌破坏。

通过与非线性动力分析结果比较，对采用非线性静力分析方法时的动力放大系数取值进行了研究。结果表明，支座杆件、跨中下弦杆、角柱和长边中柱失效情况下，动力放大系数分别取1.2、1.3、1.3和1.4时，非线性静力分析和动力分析结果最为接近。

采用增量动力分析法对结构进行了单向、双向和三向地震作用下抗连续倒塌分析，研究了杆件加固对结构抗连续倒塌性能的影响。结果表明，结构在单、双、三向地震作用下的破坏皆由上部网架屋盖倒塌引起，倒塌临界荷载分别是1.4g、0.9g、0.9g。网架结构在地震作用下的倒塌为杆件塑性发展导致的强度破坏，左下角区域腹杆为结构的薄弱部位。杆件加固后，在竖向荷载作用下，网架节点最大竖向位移比原结构减小了6.33%，极限承载力提高了8.57%，在单向、双向和三向地震作用下的倒塌临界荷载分别提高了14.29%、22.22%、22.22%，杆件加固能有效提高结构的抗连续倒塌能力。本文所取得的结论对保证网架结构的安全性具有积极的工程意义。

Grid structure roofs are widely used in public buildings such as stadiums, theaters and industrial plants. However, in recent years, collapse accidents of grid structure roof have occurred frequently, so it is particularly important to ensure that overall structures have good resistance to progressive collapse. In this paper, a three-dimensional finite element model has been established based on the actual engineering of a reinforced concrete frame structure with a grid roof system. The alternate path method has been employed to investigate the progressive collapse resistance of the remaining structure under vertical load due to the initial failure of members at different positions, and to calculate the value of the dynamic increase factor used in the nonlinear static analysis method. Additionally, the study has explored the progressive collapse resistance of the structure under seismic actions and analyzed the impact of member strengthening on the progressive collapse resistance of the structure. The main research contents and conclusions are as follows:

(1)The overall elastic-plastic analysis model of the structure has been established. Based on the stress sensitivity analysis, the sensitivity index and importance coefficient of members have been calculated, and the key members of the structure have been determined. The results show that the key members include the mid-span upper chords, support upper chords, mid-span lower chords, and support web members.

(2) The key members and lower frame columns at different positions of the grid structure have been removed by using the alternate path method, and the progressive collapse resistance of the remaining structure has been analyzed. The results show that the initial failure of a single mid-span upper chord and short side middle column will cause the progressive collapse of the grid structure, while the initial failure of a single lower chord, upper chord or web member at the support, corner column and long side middle column will not cause the progressive collapse of the remaining structures. However, the continuous failure of double mid-span lower chord or support web members will led to structural collapse.

(3) Through comparison with nonlinear dynamic analysis results, appropriate dynamic increase factor has been determined for nonlinear static analysis. The results indicate that under the failure scenarios of support members, mid-span lower chord, corner columns, and middle columns along the long side, the nonlinear static analysis results most closely align with dynamic analysis outcomes when dynamic increase factors of 1.2, 1.3, 1.3, and 1.4 are adopted, respectively.

(4) The progressive collapse resistance of the structure under unidirectional,  bidirectional, and tri-directional seismic actions has been analyzed by using the incremental dynamic analysis method, and the influence of member strengthening on the progressive collapse resistance of the structure have been studied. The results show that structural failure under all three seismic loading scenarios is primarily triggered by the collapse of the upper grid roof. The critical collapse accelerations are determined as 1.4g, 0.9g, and 0.9g for unidirectional, bidirectional, and tri-directional seismic actions, respectively. The collapse mechanism under seismic loading is attributed to strength failure caused by plastic development in members, with the diagonal web members in the lower-left corner identified as the structurally vulnerable zones. After the reinforcement of the members, the maximum vertical displacement of the grid nodes is reduced by 6.33% compared to the original structure under vertical load, and the ultimate bearing capacity is increased by 8.57%. The critical collapse accelerations under unidirectional, bidirectional, and tri-directional earthquake action are increased by 14.29%, 22.22%, and 22.22%, respectively. Member reinforcement can effectively improve the structure's ability to resist progressive collapse. The conclusions drawn in this paper have positive engineering significance for ensuring the safety of grid structures.

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