Effective Length Factor Of Column In Steel Plain Frames With Semi-rigid Connections

As important parts in steel frame, beam-to-cloumn connections play a vital role in transferring of moments and shearing forces, and their behaviors directly affect the overall behavior of steel frames. Most beam-to-column connections used in franes are semi-rigid joints, whose behavior lies between perfectly-rigid and ideally-pinned. The effect of connection behavior can be described by beam-to column connection moment-rotation curve.According to the column effective length concept of steel frames stability design and applying displacement method, the formulas for effective length factor in both braced frames and unbraced frames with semi-rigid connection are established, which are derived by taking partial frame as an analysis element, using a rotation spring which has variable stiffness to model flexibility of beam-column connection and introducing a modified stiffness factor of semi-rigid connection. The format of the formula expression regresses to that of the effective length factor of column in rigid jointed frames. The method established in this paper is easy to use. In comparison with the condition of rigid connection, the influence of semi-rigid connection to effective length factor of columns has been analyzed quantitatively.By considering semi-rigid connection with moment-rotation nonlinear behavior in whole loaded range, finite element models of steel frames with semi-rigid and rigid connections are established using ANSYS program. Nonlinear finite element analysis of steel frames with bolted and welded joints, web plate joints, T-Stub connections, two web and top-seat angles are conducted in this paper. The paper adopt the method of practical engineering match case,Through bucking analysis of sway and braced steel frames with semi-rigid connections, the effective length factor of sway and braced steel frames is derived, which considers nonlinear rotation of bolted and welded joints, web plate joints, T-Stub connections, two web and top-seat angle joints.And the effective length factor of sway and braced steel frames is derived by regression parameter considering bolted and welded joints, web plate joints, T-Stub connections, two web and top-seat angle joints.