Sway estimation of semi-rigid steel frames

Abstract

Inclusion of the inherent stiffness of the beam-to-column connections in the design practice would make the structure economical compared to those designed using the conventional 'pin' or 'rigid' frame assumptions. The overall behavior of the multistoried frames is highly dependent on the connection characteristics. Research on the semi-rigid sway steel frames indicates that the recommended limit on sway rather than the ultimate strength governs the design of these frames. This thesis contains a numerical study on the behavior of multi-storied semi-rigid steel frames. The finite element (FE) models developed here have been extensively verified against earlier research works. Frames ranging from five to thirty stories high having a wide range of connection flexibility have been analyzed with a view to get some simplified methods for calculating sway. Two independent methods, a graphical method using nomographs and an equation, have been proposed to estimate sway of regular steel frames. •• Non-regular frames are also studied and proposals have been made to include the sectional as well as geometrical irregularities while calculating sway of such frames. By studying the nonlinear moment-rotation behavior of semi-rigid steel connections, a method is proposed for hand calculation of connection stiffness. Most of the steel frames are partially flexible at the base as well as at beam-to-column connections. The extent of the effect of base flexibility on the sway of steel frames studied here and a nomograph is proposed to include the effect of base flexibility in the sway calculation. Worked examples are given to illustrate the proposed design methods. The findings are used to develop a unified design procedure for any semi-rigid steel frame possessing all possible variations within the specified range.