Analysis of semi-rigid steel frames and criteria for their design

Abstract

This paper reports studies on unbraced semi-rigid steel frames, carried out to determine criteria for their design. The analyses of the frames were performed by a computer program that uses a secant-stiffness approach to allow for the effect of semi-rigid connections on frame behaviour. A parameter entitled ‘degree of flexibility’ is introduced as a measure of the effect of semi-rigid joints on the stiffness of the frame. Within the limits of the study, it is demonstrated that second-order effects will not be significant if the semi-rigid elastic critical load exceeds ten times the design load, and the degree of flexibility is less than 50%. This last requirement was satisfied by extended end-plate beam-to-column connections. It has also been found that, under combined loading, the serviceability limit on sway is likely to control design, rather than ultimate strength.