抄録
According to AIJ-Specification for Steel Construction, the magnitude of the bracing strength must be taken as F≥0.02P where P is equal to compressive force and F is the bracing strength. However, in a case where a lateral support has nots sufficient stiffness, even though its strength is large enough, the compression member deflects excessively and its strength does not reach the expected strength P_<cr>, which is the strength of the fully braced member. Hence the lateral support with insufficient stiffness does not play a role of support. Up to the present, few precise studies on this problem have been done. Therefore, in this paper, we examined, first of all. the lower bounds of sufficient bracing strength and stiffness in order that compression members with initial imperfections, hinged at both ends and laterally supported at the center, can reach the expected strength P_<cr>. Then the following conclusion is obtained. "Even though the lateral support of a compression member has the larger strength than 0.02P_<cr>, the strength of the compression member cannot reach P_<cr> unless the stiffness of the lateral support k satisfies the following requirement, k/k_0≥0.7 where k_0=0.02P_<cr>/(L/1000). The above requirements are available when the slenderness ratios of compression members L/i are within the range, 20≤(L/2)/i≤200
