End-plate connections and analysis of semi-rigid steel frames
The thesis examines the behaviour of end-plate connections and the related topic of analysis of unbraced semi-rigid steel plane frames with criteria for their design. The static moment-rotation behaviour is investigated for connections consisting of bolted flexible end-plates, flush and extended end-plates, between I-section members, where the beams frame into the flanges of the columns. Attention is focussed on moment-rotation characteristics as this is the most important influence on the response of either individual members or complete frames. The non-linear nature of these characteristics is identified and methods of representing moment-rotation curves for subsequent use in analytical procedures are presented. A data base for such types of connection is created. An established computer program for second-order frame analysis has been extended to frames with semi-rigid connections. Successive estimates are made of the secant stiffness of these connections to represent their effect on frame behaviour. The analysis program has been used to study the effects of semi-rigid joints on frame behaviour. Studies have been carried out to extend the Merchant-Rankine formula for the assessment of the ultimate load of frames with semi-rigid joints over the application range of which was until now restricted to frames with rigid joints. 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 the 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. Based on experimental and theoretical studies, it is recommended that the BS5950 simplified method should permit 20% end-restraint, which would improve significantly the attractiveness of the method.