中心支撑钢框架顶部薄弱层地震倒塌现象

Phenomenon of seismic collapse of top weak story of CBSF

现行抗震规范和相关规范、规程对高层结构侧向刚度自下而上的减小幅度缺乏定量规定,仅通过非强制性条款进行了定性描述。文章通过具体算例证明了可能导致在某些设计中出现高层中心支撑钢框架顶部各层的刚度减小过快的情况,尽管满足了抗震规范和相关规范、规程的规定,但结构仍有可能出现顶部薄弱层倒塌现象;并指出应该定量地限制结构沿高度方向的刚度减小削弱幅度,以避免该类现象的发生。

Although there are some qualitative and non-compulsory regulations about the decrease of lateral stiffness of high-rise structure along height direction, the decrease ratio of lateral stiffness is not provided in the present seismic code and relative code. In this paper, it is illustrated that the defi ciency probably leads to the too fast decrease of top story stiffness of high-rise concentrically braced steel frames（CBSF） in some designs, and the top weak story possibly collapses when the other stories are still in rather safe state under strong earthquakes. Thus quantitative provisions about the decrease ratio of the lateral stiffness along height direction should be provided to eradicate the latent danger of top weak story collapse under strong earthquakes.