Clarification of Unstable Behavior of Building Steel Frames Subjected to Repeated Loading and Development of Estimation Method of Safety

为了阐明框架结构的不稳定性，并建立一种安全性评估方法，本文进行了一系列的理论和数值研究。研究结果如下：1.通过对称极限分析，发现了一种新的H形单肢框架临界行为，并阐明了其出现的条件.多层多跨平面框架的一种新的临界行为，其特征是跨越一定层数的弓形柱挠度模态的循环增长。如果柱力超过一定的极限，这种临界行为是可能发生的，这可以通过对称极限理论来预测。从理论上阐明了柱挠度模态出现和周期指数增长的机理.对几个多层框架结构在简谐地震动和记录地震动作用下的动力反应进行了分析。结果表明，在重复地面运动的动力响应中，也可以出现与静力行为中观察到的柱挠度模式类似的柱挠度模式.动地震动反应中该临界行为的出现极限条件和变形模式与静力重复荷载下的临界行为的出现极限条件和变形模式一致.由于该极限状态仅由框架本身的参数决定，因此对框架结构的抗震稳定性评价和实际抗震设计具有一定的参考价值。

A series of theoretical and numerical studies have been carried out to clarify the unstable behavior of framed structure, which can not be captured with any simplified method of numerical analysis used in design practices, and to develop an estimation method of safety. The results obtained by these studies are summarized as follows :1. A new type of critical behavior in a H-shaped simple unit frame has been found and its appearance condition has been clarified by performing a symmetry limit analysis.2. A new type of critical behavior of multi-story multi-span planar frames, which is characterized by cyclic growth of a bow-shaped column deflection mode spanning a certain number of stories. This critical behavior is possible to occur, if the column force is in excess of a definite limit, which can be predicted by the symmetry limit theory. The mechanisms of the appearance and cyclic exponential growth of the column deflection mode have also been clarified theoretically.3. Dynamic response analyzes have been performed on some multi-story frames subjected to harmonic ground motions and recorded seismic ground motions. It has been shown that a similar type of column deflection mode to that observed in the static behavior can appear also in the dynamic response to the repeated ground motions.4. Both the appearance limit condition and the deflection mode of this critical behavior in the responses to the dynamic ground motions well coincides with those of the critical behavior under statically repeated loadings.5. Since the limit condition is to be determined by the parameters of the frame itself only, then it should be useful for the estimation of seismic stability and practical seismic design of framed structures.