The strength of biaxially loaded beam-columns in flexibly connected steel frames
This thesis describes the experimental appraisal of a series of 10 'non-sway' steel column subassemblages, each comprising a 6m long column with up to three 1.5m long beams, together with two full-scale 3 storey, 2 bay, single span, non-sway steel frames (typical overall dimensions 9m x 10m x 3.5m). The subassemblages tests were conducted in the Department of Civil and Structural Engineering at the University of Sheffield whilst the much larger frame tests were carried out at the Building Research Establishment. In all cases, the beam and column elements were connected using 'simple' bolted steelwork connections. The aim was to investigate the effect of the inherent rotational stiffness (semi-rigid characteristics) of such connections on the behaviour of steel frames in which the columns were loaded biaxially and were not restricted to in-plane deformation. The appraisal of the results from these experiments clearly shows that the stiffness of even the most modest connection can have a significant influence on the distribution of bending moments, the ultimate column capacity and deflection of frame members. The experimental data were subsequently used to validate the predictions of a sophisticated finite-element computer program which was developed specifically to analyse 3-dimensional column subassemblages employing semi-rigid connections. This thesis documents this validation and reports the findings of an extensive parametric study which was then conducted to investigate the influence of semi-rigid connection behaviour on a wide range of subassemblage configurations. Comparisons with the experimentally observed and analytically predicted ultimate capacities of the subassemblage and frame tests showed that 'commonly used' methods of frame design are unduly conservative. The author has therefore proposed a number of design approaches for both ultimate and serviceability limit state loading conditions which take into account the inherent benefits of semi-rigid joint action.