Study On The Effective Length Factor Of Concentrically Braced Member With Gusset Plate Connections

In order to develop the plastic rotation capacity of the gusset plate, the out-of-plane buckling of the bracing member has to be ensured in the concentrically bracing frame with gusset plate connections, which means that the low-cycle ability of the connection can be fully used. The out-of-plane slenderness ratio should be greater than the in-plane slenderness ratio to ensure the out-of-plane buckling of the bracing member. However, in GB50017-2003, the constraint condition of the bracing member is assumed as hinged joint, which stipulates that the out-of-plane effective length factor is 1.0, and the in-plane effective length factor is 0.8, considering the in-plane stiffness of the gusset plate. This method is obviously conservative, which means that it is difficult to determine the critical value to ensure the out-of-plane buckling of the bracing member.In this paper, the integrated model was established by ABAQUS, the effective length factor(in-plane and out-of-plane) of concentrically braced member was calculated by eigenvalue buckling analysis. And the critical models which the bracing member fluctuated between out-of-plane buckling and in-plane buckling were established to determine the matching ratio of the out-of-plane effective length factor and the in-plane effective length factor, to ensure the the out-of-plane buckling of the bracing member, and to provide reference for design. The main contents are as follows.1. The integrated model was established, and the effective length factor of concentrically bracing member was calculated by eigenvalue buckling analysis. Parameter analysis was done to gain the influence factor of the effective length factor when the slenderness ratio, the thickness of the gusset plate, geometric offset and the angle of the bracing change were taken into consideration. Suggested formulas which could envelope all the data were proposed based on the parameter analysis.2. Nonlinear analysis was done due to the model of eigenvalue buckling analysis to gain the bearing capacity which is compared with the value calculated according to the design code, verifying the feasibility of the model and the accuracy of the analysis method.3. Chevron bracing model and cross bracing model were established to obtain the effective length factor. Parameter analysis was made and the result was compared to single diagonal bracing member. Suggested formulas were therefore proposed based on the parameter analysis.4. Critical model was established and then the eigenvalue buckling analysis. The out-of-plane and the in-plane slenderness ratio were changed by changing the parameter of the bracing members. Moreover, the matching ratio of the out-of-plane effective length factor and the in-plane effective length factor is determined to ensure the the out-of-plane buckling of the bracing member.