# Limit State Design of Sway Frames

*A significant feature of multistorey sway frames is the drastic effect of horizontal deflections on their stiffness. This applies particularly with tall and irregular frames, where controlling the sway, to satisfy limit state recommendations, is more difficult than satisfying strength and instability requirements. In this paper a simple, but accurate, method is presented for the design of these frames. An equation is first derived to define the most economic profile of a frame in its deformed position. A practical design method is then presented in which the member sizes are calculated so that the storey deflections, as given by the profile, are satisfied exactly. The method is fast because it does not depend on the analysis of the frame with preselected sections and thus removes the need for the explicit solution of any simultaneous stiffness equations. Instead, it proportions the members in the most economic manner, using current market prices, and calculates the required column sections. A design procedure is given so that all the recent BSI recommendations for the limit state design of steel sway frames are satisfied. The results of an investigation into the design of sway frames are then reported, in conjunction with a number of examples.
Professor K.I. Majid and S. Okdeh*