某带高位长悬挑桁架的超限结构设计

Design on an out-of-code structure with large-span and high-position cantilever truss

南京扬子江国际会议中心是海峡两岸企业家峰会永久会址,其C区单体外观和内部空间形态复杂多变,是具有6项不规则的超限结构。本单体4层至5层采用单斜拉腹杆布置的跨层钢桁架搭建悬挑12.9~14.6m的高位长悬挑空间。结构分析发现:时程法计算所得竖向地震系数可能大于等效静力法和反应谱法,需进行包络设计;在悬挑根部并沿向内跨延伸方向的楼板拉力较大,需对楼板进行加强,而改进施工次序后的无支撑安装法可以显著减小楼板拉力;悬挑侧桁架构件多由非地震工况控制,根跨构件多由地震工况控制;在通高桁架轴跨中部增加立柱可以增强悬挑桁架的空腹桁架作用,增强结构的防连续倒塌能力;合理布置TMD可以有效降低悬挑桁架的竖向振动加速度,从而满足舒适度设计要求。

Nanjing Yangtze River International Conference Center is the permanent site of the Cross-Strait CEO Summit. Building C of the project has a complex appearance and internal space, and is an out-of-code structure with 6 irregular items. A large-span and high-position cantilever space from the 4 th to 5 th floor of this building is built by a 12.9~14.6 m length steel truss with tensile diagonal web members. Structural analysis indicates that: the vertical seismic coefficient taken by time history method may be larger than that taken by the equivalent static method and the response spectrum method, and envelope design was required. The slab near the root of the truss and along the force direction of the inner span needs to be strengthened because of the large tensile force, and the construction sequence of unsupported installation method is improved to significantly reduce the floor tension force. The cantilever side members of the truss are mostly controlled by non-seismic load condition, meanwhile the root span members are by seismic load condition. The vierendeel truss effect of the cantilever truss can be improved by vertical columns placed in the middle span of the through-height truss, which increases the progressive collapse prevention ability of the structure. Reasonable arrangement of TMD can effectively reduce the vertical vibration acceleration to improve the comfort of the cantilever truss.