中文摘要：

为了研究地震作用下钢框架结构的落层倒塌效应，根据相关文献提供的9层钢框架模型，利用非线性显式动力有限元程序LS-DYNA分析其在地震作用下的结构响应，同时模拟相关文献中的振动台结构倒塌试验，分析结果同文献对比较为吻合，验证了模型的合理性。对该钢框架在强震作用下的倒塌效应进行仿真，分析表明强震作用下首先由于结构中部薄弱层层间位移角发展达到1／10并持续增大，发生落层倒塌，上部楼层碰撞作用于下部楼层，使下部相邻楼层柱轴力突增，加剧该层P-4效应，导致下层倒塌；此外第1层层间位移角亦发展达到1／10并持续增大，继而导致钢框架整体发生连续倒塌破坏。分析了落层倒塌碰撞作用下，薄弱层相邻下层柱总轴力变化规律，其动力放大系数可能大于规范取值。加强薄弱层抗侧刚度可有效防止钢框架发生倒塌破坏；合理设计的钢框架结构当薄弱层层间位移角超过规范限值但未出现持续增大现象时，不出现倒塌破坏。

英文摘要：

A numerical model based on the explicit finite element package LS-DYNA was proposed to investigate the pancake collapse response of a 9-story steel frame under seismic action. The numerical model was validated by a shaking table collapse test for a spacial slab-column structure, and then the pancake collapse process of the steel frame was simulated and analyzed. It is found that the drift angle of the weak story expanding larger than 1/10 leads to pancake collapse, then the upper part of the structure moves downwards and collides with the lower part of the structure, and causes a large axial force in the sub-story column, which expands the P-A effect and leads to progressive collapse of the steel frame. The dynamic increase factor of the sub-story column may be larger than the proposed value in the code. It is indicated that the pancake collapse can be prevented by enhancing the lateral stiffness of the weak story, and the collapse would not happen by a reasonably design if the drift angles of the story converge though larger than the code limit.