Effective Length Factor Of Columns In Two Web And Top-seat Angle Semi-rigid Connected Steel Frames

Most beam-to-column connections used in frames are semi-rigid joints, whose behavior lies between perfectly-rigid and ideally-pinned. The effects of connection behavior can be described by beam-to-column connection moment-rotation curve. In order to describe the effects with two web and top-seat angle connections, this paper introduces the three-parameter power model of moment-rotation curve. The initial secant stiffness (R_i0 )and effective stiffhess(R_b) of connections are used in the analysis of effective length factor of columns in non-sway and sway frames respectively.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.Nonlinear finite element analysis of steel frame with two web and top-seat angle connections is conducted in this paper,and the buckling loads of this frame are gained, The results shows good degree with the resusts caculated by theoretical formulas ,thus the appropriation of theoretical formulas are verified.