合成ばり架構の弾塑性応答解析法および応答性状に関する研究

Abstract

This paper examined for the dynamic elastic-plastic response of framed structures composed of composite beams under the earthquake loading. The elastic-plastic incremental stiffness matrix of composite beams is derived based on the Newmark's differential equation and on the generalized hinge method. When the composite beams framed structure are subjected to the earthquake loading, both positive and negative bending moment act on beams, so that composite beams behave as varying cross section members. The elastic stiffness of composite beam is affected by the distance from end support to the point of zero bending moment and the shear connector stiffness, and so on. In this paper, the influence of these factors on stiffness are investigated, and the method of evaluating the elastic stiffness of composite beams are presented. Further, the plastic incremental stiffness is derived according to the concept of generalized plastic method. The member end moment vs. end rotation relationship of composite beam analized by this stiffness matrix is in Figure (3-7). Next, using the elastic-plastic stiffness matrix, the composite effects on the dynamic elastic-plastic response of multi-story multi-bay building frames are examined against earthquake excitation. The frames used in the analysis are designed according to the plastic design method. The results may be summarized as follows : 1. If shear connector stiffness per unit length is more than about 0.5 percent of Young's modulus of steel, the influence of slip between interacting elements on the elastic stiffness of composite beams can be ignored. 2. By using elastic-plastic incremental stiffness matrix, a reversed S-shaped type of hysteresis loops of composite beams can be shown (See Figure (3-7)). 3. The displacement response of frames composed of composite beams shows a tendency to become greater than that of steel frames, however this tendency is not so remarkable. 4. The collapse mechanism of the frames, which composite effect is not taken into account in design process, reduce to column yield type sway mechanism. And the displacement response of this type of frame tend to concentrate in the lower stories.