钢框架高等分析中初始几何缺陷的考虑方法

Consideration of Initial Geometric Imperfections in Advanced Analysis for Steel Frames

结构整体和构件的初始几何缺陷是结构产生非线性行为的影响因素之一,在目前的高等分析中常按最不利的缺陷分布来考虑它们的影响。采用蒙特卡罗法可以考虑初始几何缺陷的随机遇合问题,能更加合理地确定初始缺陷的分布规律。通过统计分析得到柱顶侧移和梁跨中挠度的概率密度函数,可由此确定框架可能的最大变形。某一六层单跨框架的计算结果表明:当按缺陷的最不利分布来施加不同的初始几何缺陷时,对框架的极限承载力影响不大,但对框架的侧向变形影响较大:初始几何缺陷越大,框架的最终变形也越大。但按蒙特卡罗法考虑不同的初始缺陷时,与无缺陷框架相比,结构变形增加有限。算例还表明,当框架按高等分析的极限承载力设计时,相应标准荷载作用下的变形不能满足正常使用要求,因此,设计常受正常使用极限状态控制。

The initial geometric imperfections of global system and individual members,which is one of the factors contributing to nonlinear behavior of structure,should be taken into account by the most unfavorable combination of imperfections in advanced analysis generally. The distribution of initial imperfections could be determined reasonably by the Monte Carlo method,because the random combination of the initial imperfections between columns and beams can be considered reasonably; probability density functions of lateral displacement and mid-span deflection are proposed through statistics analysis,and the possible maximum deformation of frame is also obtained. The analysis results of the six-story frame indicate that the ultimate bearing capacities are roughly identical by taking different initial geometric imperfections under the most unfavorable combination,but the effects on the lateral deformation of frame are obvious. The larger the initial geometric imperfections,the more significant the lateral deformations of frame. The increment of the frame deformation by Monte Carlo method is little contrast with the results of the ideal frame. The analysis results also indicate that when the frame is designed by the ultimate capacity of advanced analysis,the deformation in the relevantly normal loading could not satisfy the requirement of the serviceability limit states. For this reason,the design of the frame should be controlled by the serviceability limit states.