Effect of gravity columns on mitigation of drift concentration for braced frames
Effect of gravity columns on mitigation of drift concentration for braced frames
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DOI：
10.1016/j.jcsr.2009.07.003
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发表时间：
2009-12-01
影响因子：
4.1
通讯作者：
Nakashima, Masayoshi
中科院分区：
文献类型：
--
作者：
Ji, Xiaodong;Kato, Mikiko;Nakashima, Masayoshi
在强震事件中，多层同心支撑钢框架（CBF）在层内支撑屈曲和屈服后容易形成层倒塌机制。然而，通过增加连续重力柱以及它们提供的增加的横向刚度和强度，可以减少楼层漂移的集中并防止楼层倒塌。对三层CBF进行非线性动力分析，结果表明，当CBF受到50年内概率超过2%的一组大地震动时，漂移集中是不可避免的，特别是在第一层。提出了一个简化的理论公式来表征重力柱的影响。考虑两种情况：重力柱完全固定，以及重力柱固定在底座上。值得注意的是，可以实现漂移浓度的显着减轻，特别是当重力柱固定在底座上时。进一步进行非线性时程分析以验证理论观察结果并量化重力柱的刚度/强度需求，以避免漂移集中。分析结果支持从理论公式中获得的趋势和观察结果。最后以地震力折减系数Ds、支撑长细比x、层数为主要分析变量进行数值模拟。结果表明，少数（例如四个）固定底座重力柱可以在大地震动作用下实现合理设计的低层循环流化床的防倒塌作用。 (C) 2009 Elsevier Ltd. 保留所有权利。
In strong earthquake events, multi-story concentrically braced steel frames (CBFs) are prone to form a story-collapse mechanism after buckling and yielding of the braces in a story. With the addition of continuous gravity columns and the increased lateral stiffness and strength they provide, however, it becomes possible to reduce the concentration of story drift and prevent the story collapse. Nonlinear dynamic analysis is implemented for a three-story CBF, and it is demonstrated that a drift concentration is inevitable, particularly in the first story, when the CBF is subjected to a set of large ground motions with a probability of exceedance of 2% in 50 years. A simplified theoretical formulation is presented to characterize the effect of gravity columns. Two cases are considered: gravity columns perfectly fixed, and gravity columns pinned at the base. It is noted that significant mitigation of drift concentration can be achieved, particularly when gravity columns are fixed at the base. Nonlinear time-history analysis is further performed to validate the theoretical observations and quantify the stiffness/strength demands of gravity columns to avoid drift concentration. The analysis results support the trends and observations obtained from the theoretical formulation. Finally, numerical simulations are implemented with the seismic force reduction factor Ds, slenderness ratio of braces x, and number of stories, as major analysis variables. The results demonstrate that a few (e.g. four) fixed-base gravity columns can lead to collapse prevention for reasonably designed low-rise CFBs under the set of large ground motions. (C) 2009 Elsevier Ltd. All rights reserved.