摘要:
大跨度柔性及半刚性结构由于索单元的引入, 显著提高了结构的受力性能, 使得更多满足建筑创新要求的结构得以实现。近年来上述两种结构被广泛应用于大型体育场馆, 国内外学者对其进行了大量理论研究, 且研究成果已较好地用于实际工程中。因柔性和半刚性结构对索单元依赖程度的差异, 两种结构在竖向刚度及索力敏感程度方面产生了较大差异, 该差异对实际的设计及施工产生了巨大影响。为探究上述问题, 通过通用有限元软件ANSYS建立相同尺寸的大跨度轮辐式双层索网和辐射式张弦梁结构, 以竖向刚度和索力敏感程度为目标设立相应的对比参数, 包括等效竖向刚度系数G、索力敏感程度值TS1和索力敏感程度相对值TS2, 对多组不同跨度的两种结构进行对比分析, 以指导相似工程的设计工作。结果表明: 在外荷载不断增大的过程中, 索网结构的竖向刚度存在突变和缓慢增强的现象, 通过对环向索(构造索)的内力进行跟踪记录后发现, 在刚度突变点, 环向索内力逐渐由正值降为零(发生松弛), 说明环向索的松弛现象导致结构竖向刚度发生突变; 通过相关数据分析可知, 相比于荷载施加初期的刚度, 索网结构荷载施加末期的刚度增加约3.2%, 因增加量较小, 实际分析中可忽略不计。张弦梁结构的竖向刚度基本保持不变且不存在刚度突变现象。当跨度较小时, 索网和张弦梁的等效竖向刚度系数G较为接近, 随着跨度的增大, 两种结构均出现等效竖向刚度系数G下降的现象, 但索网结构下降速率远快于张弦梁结构。相同平面布置情况下, 索网结构的索力敏感程度值TS1、索力敏感程度相对值TS2均大于张弦梁结构, 表明索网结构对索力的敏感程度较小, 而张弦梁结构由于上部刚性杆件的存在, 整体刚度在较小索力的情况下已经形成, 使得该结构对索力敏感程度加强。在增大预应力或减小跨度的过程中, 索网和张弦梁结构均出现对索力敏感程度减弱的现象。对索网与张弦梁结构的索力敏感程度值TS1进行比较后发现, 两种结构的TS1比值稳定在2.43~2.55之间, 该结果可为相似工程提供参考。
Abstract:
Due to the introduction of cable element, the mechanical performance of long-span flexible and semi-rigid structures is significantly improved, so that more structures meeting the requirements of architectural innovation can be realized. In recent years, the above two kinds of structures are widely used in large stadiums and gymnasiums. Scholars at home and abroad have done a lot of theoretical research on them, and the research results have been well used in practical engineering. Due to the difference of the dependence of flexible and semi-rigid structures on cable elements, there are great differences in the vertical stiffness and the sensitivity of cable forces between the two structures, which makes large effects on the actual design and construction.In order to explore the above problems, large-span spoke double-layer cable net and radial beam string structures with the same size were established by using the general finite element software ANSYS, and the corresponding contrast parameters were set for the vertical stiffness and cable force sensitivity, including the equivalent vertical stiffness coefficient G, the cable force sensitivity value TS1 and the cable force sensitivity relative value TS2. Comparative analysis was carried out to guide the design of similar projects.The results showed that: in the process of increasing the external load, the vertical stiffness of the cable net structure had the phenomenon of mutation and slow enhancement. Through tracking and recording the internal force of the circumferential cable (structural cable), it was found that the internal force of the circumferential cable gradually decreased from positive value to 0 (relaxation) at the point of stiffness mutation, which indicated that the relaxation of the circumferential cable led to the mutation of the vertical stiffness of the structure. According to the data analysis, compared with the initial stiffness of the load, the final stiffness of the cable net structure increased by about 3.2%, which could be ignored in the actual analysis because of the small increase. The vertical stiffness of beam string structure was basically unchanged and there was no sudden change of stiffness. When the span was small, the equivalent vertical stiffness G of cable net structure and beam string structure was close. With the increase of span, the equivalent vertical stiffness G of both structures decreased, but the decline rate of cable net structure was much faster than that of beam string structure. Under the same plane layout, the cable force sensitivity TS1 and the relative value TS2 of the cable net structure were greater than that of the beam string structure, which indicated that the cable net structure was less sensitive to the cable force, while the overall stiffness of the beam string structure had been formed in the case of small cable force due to the existence of upper rigid members, which made the structure more sensitive to the cable force. In the process of increasing prestress or reducing span, the sensitivity of cable net and beam string structure to cable force decreased. After comparing the cable force sensitivity value TS1 of cable net and beam string structure, it was found that the TS1 ratio of the two structures was stable between 2.43 and 2.55, which could provide reference for similar projects.