灾害风荷载下温室单层柱面网壳整体动力倒塌分析

该文针对大跨轻质单层柱面网壳在灾害强风天气下存在动力倒塌破坏的可能性,利用显式有限元分析软件ANSYS/S-DYNA及自编前后处理程序,综合考虑了几何非线性、材料非线性和接触非线性,建立了灾害风荷载下温室单层柱面网壳结构整体动力倒塌的数值分析模型,考察了单层柱面网壳的动力倒塌发展全过程。以节点位移和变形形态等几何特征响应对网壳结构进行了动力倒塌过程分析,将网壳结构倒塌过程依据其特性划分为轻度损伤阶段,倒塌形成阶段和整体倒塌阶段3个阶段;同时以杆件内力和截面塑性发展等力学特征响应对网壳结构进行了动力倒塌机理研究,指出网壳结构的风致动力倒塌原因是风压区压杆反复屈曲和拉杆依次失效相互作用的综合体现。对比分析考虑下部支承与不考虑下部支承单层柱面网壳的动力倒塌过程,结果表明,考虑下部支承柱时网壳结构动力倒塌对应的临界荷载系数发生了25%的明显降幅。该研究为温室网壳结构的抗风设计、工程应用和防灾评估提供了理论参考。

Global dynamic collapse analysis of single-layer cylindrical reticulated shell in greenhouse under disaster wind loads

Abstract: Single-layer cylindrical reticulated shell structures with the advantages in providing powerful transfer loads capability, large span space, excellent economic index, good light transmission performance and beautiful architectural style, not only are widely used in civil engineering, but also get more and more use in greenhouse construction because they can meet the requirement of rapid development of facility agriculture. Considering the high frequency of disaster winds in many regions of China, and the characteristics of reticulated shell structure including low overall stiffness, numerous vibration modes and great sensitivity to wind loads, the dynamic collapse may occur for single-layer reticulated cylindrical shell structure with large span and light weight in the weather of severe disaster winds. To analyze the collapse mechanism and the influence factor of this type of structure under wind loads is very important for the engineering design and theoretical analysis. In this paper, the analysis model of global dynamic collapse for single-layer cylindrical reticulated shell structure of greenhouse under wind loads was established by considering geometric nonlinearity, material nonlinearity and contact nonlinearity. In the numerical analysis, the effective plastic strain was defined to simulate the failure of tension members. To illustrate the influence of dynamic buckling of compression members on the collapse of the structure, each member was equally divided into 6 beam elements. The finite element explicit analysis software ANSYS/LS-DYNA was employed, and the dynamic buckling of compression members was considered. The collapse process of reticulated shell was analyzed and then was showed with the maximum nodal displacement, the deformed configuration and the plastic member distribution of the structure at different time. Based on the numerical analysis results and performance of the structure, the collapse process of reticulated shell was divided into 3 stages, which were named mild damage stage, collapse formation stage and overall collapse stage respectively. During the first stage (from the beginning to 21.7 s), the reticulated shell was generally in a deformation recoverable state with only a few members entering the plastic state in the compression area of the center and both ends of the structure. Therefore no local collapse occurred and little damage was produced to the structure performance. In the second stage (from 21.7 to 22.6 s), a series of dynamic buckling of members in the wind pressure zone from the bottom to the top of shell occurred, and a band-like buckling region was formed. At the same time, a number of tensile members entered the plastic state and gradually formed a plastic area. This weakened the stiffness of the structure, caused the structural vibration equilibrium position to deviate from its initial position, and finally caused the local collapse in the compression area of the structure. In the third stage (after 22.6 s), the plastic deformation of members in the buckling area of the reticulated shell reached its failure strain at first, and then the fracture failure of the members occurred. Under continuous dynamic forces, the collapse area rapidly expanded with the time, and finally led the shell to lose structural integrity completely at 24.8 s. In addition, considering most of the reticulated shell structures were supported with substructure, this paper also investigated the influence of substructure on the dynamic collapse performance of the upper reticulated shell under wind loads. The same reticulated shell model used above but without substructure was analyzed. The results of calculation showed that the load factor of the collapse of reticulated shell with substructure was reduced by 25% compared with that of the reticulated shell without substructure. The substructure would weaken the stiffness of the whole structure, and therefore reduce the wind loads bearing capacity of reticulated shell structure. It was necessary to consider the influence of substructure in the dynamic collapse analysis of reticulated shell structure under wind loads. Otherwise, the wind loads of the collapse of reticulated shell would be over-estimated. Based on the analysis results, some conclusions are drawn, which provide the basis theoretical reference for engineering analysis and further studies of reticulated shell structure in modern greenhouse.