国家游泳中心“水立方”结构设计优化

Structural Design Optimization of National Swimming Center "Water Cube"

国家游泳中心“水立方”的墙体和屋盖结构创造性地采用了新型多面体空间刚架结构体系,该结构的弦杆选用矩形钢管、腹杆选用圆钢管,节点为焊接球节点。虽然结构的构成类似网架结构,但结构构件的受力状况完全不同于网架结构的二力杆,而表现为类似空腹网架的刚接梁。杆件内力包含弯矩、轴力、剪力、扭矩,弯曲应力大于轴向应力,所以结构的优化较为复杂。本文结合具体的结构设计,全面介绍了结构设计计算中的优化内容,包括:“强墙弱盖”优化,墙体杆件和屋盖杆件选用不同应力水平控制;截面类型优化,放弃加劲肋截面而改用紧凑型截面,充分发挥截面塑性,提高结构延性;几何构成“杂交”优化,将屋盖下弦贯通内墙,为减小屋盖与墙体交界处杆件过大的弯曲应力而附加少数腹杆,形成局部汇交力系;“铰接”优化,采用铰接计算处理策略,将少数弯曲应力较大无法满足规范要求的杆件两端处理为铰接,加强其周围相关杆件,再刚接迭代计算,较好满足承载力要求;“强节点弱杆件”优化,提高结构延性,确保杆端焊缝破坏晚于杆件屈服。

Polyhedron space frame structure is created and adopted in the National Swimming Center “Water Cube” for the first time in the world. In which, rectangular hollow sections are used as chords, circular hollow sections are used as web members and welded hollow balls are used as joints. Although the form of the new structure is like space truss, the member behavior is entirely different from the truss member which mainly bearing axial force, the polyhedron space frame member is like the beam with rigid connection in Vierendeel truss. The joints are rigidly-connected nodes and the members are space frame elements. Element forces contain bending moment, axial force, shear force, torsional moment, the moment stress is larger than axial stress. The main optimizations of the structural design is presented in this paper as follows. “Strong wall and weak roof” optimization, in which the control stress levels in wall members are lower than those of the roof members. Section type optimization, that is instead of using the original section with longitudinal stiffener, the compact section is adopted, and the plastic property of compact section is utilized so as to enhance the section ductility. Hybrid optimization of geometric constitution, that is to decrease the bending stresses of members near the boundary of wall and large span roof, some web members are added to form a local joining force system. “Pin” connection release calculation strategy, that is to set end release to the elements with large bending stresses, to strengthen the corresponding around members, then calculating as rigid connections by iteration with software autormtically. Robust joint details avoid the weld crack occurring earlier than member yielding.