国家体育场大跨度钢结构设计与研究

Design and research of large-span steel structure for the National Stadium

在国家体育场设计中,利用CATIA空间建模软件建立了国家体育场大跨度钢结构精确的三维空间几何模型与计算模型。为了使结构受力合理、减小构件加工制作难度与施工的复杂性,主桁架弦杆在相邻腹杆之间采用直线代替空间曲线构件,桁架柱腹杆尺寸与菱形内柱同宽。对于屋盖肩部的空间扭曲构件,在整体计算模型中用分段折线代替理想曲线,并对每段构件截面的主轴方向进行偏转。屋顶与立面次结构可以有效减小主结构弦杆面外的计算长度,提供ETFE膜结构、下弦声学吊顶与屋面排水系统的支承条件,并形成结构的抗侧力体系。在设计中运用将“死”单元逐次激活的技术,对钢结构在整个施工过程刚度和荷载的变化情况进行模拟。根据风洞试验确定风压分布,提出下风振系数的计算方法,确定大跨度结构的风振下压效应。采用新型国产高强钢材,并根据构件的重要性确定钢材的技术性能要求。在综合考虑工程的重要性、结构受力特点、施工偏差以及工程造价等多种因素的基础上确定构件应力比限值,进行构件优化计算。对恒荷载、活荷载、风荷载、温度作用、小震与中震及相应的工况组合进行计算,并对材料利用率与结构用钢量进行了分析统计。

In the design of the National Stadium, the precise 3D geometrical model and calculation model for large-span steel structure was established by use of CATIA dimensional modeling software. In order to rationalize loading of the structure, reduce the difficulty in fabrication of the members and complexity in construction, straight line members are adopted in primary truss chords to replace spatial curve members between neighboring diagonals. The diagonals of the trussed column are as wide as the diamond inner column. As for the dimensional twisted members at the shoulder of the roof system, sectionalized break lines replace ideal curve, and the main axis of the section of each member is deflected. Roof top and facade secondary structure can effectively reduce the out-of-plane calculated length of the primary chords, and provide support conditions for ETFE cladding structure, acoustic ceiling at the bottom chord and roof drainage system, forming the lateral force resisting system for the structure. The technique to reactivate the ＂dead＂ element step by step is employed in the design so as to simulate the changes in stiffness and load of the steel structure in the construction process. Wind pressure distribution is identified based on the result of wind tunnel test, and the calculation method for wind-induced oscillation coefficient is proposed to determine the compression effect of wind induced oscillation in large -span structure. A new type of domestic-made high-strength steel is employed, and the technical performance requirements are determined according to the importance of the members. Limit of stress ratio of the members is determined and member optimization calculation is made by taking into full consideration various factors such as the importance of the project, the loading feature of the structure, and construction error and project cost. Dead load, live load, wind load, temperature effect, minor earthquake, intermediate earthquake and related load combinations are calculated, meanwhile the utilization ratio of the materials and steel tonnage of the structure are surveyed.