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.