ABSTRACT
It was early in the last century that laboratory studies (Young and Jackson 1934, Rathbun 1936) of the behaviour of practical forms of (riveted) beam to column connections for steel frames revealed that nominally pinned arrangements actually possess some degree of rotational stiffness. Research in this area (Benussi et al 1989, Anderson and Najafi 1994, Xiao et al 1994 and Li et al 1996), especially over the past two decades, has provided methods for estimating this stiffness for a number of practical arrangements. When it is recalled that the central deflection of a fixed-ended beam is only one fifth that of an equivalent simply supported beam, it becomes clear that allowing for even modest degrees of end fixity when estimating serviceability deflections should lead to worthwhile benefits. This is all the more important when it is realised that such benefits are achievable with no change to established practice-rotational stiffness is present in the joints even though it is not normally allowed for in the calculations. In this context it is of interest to note that when pre-cambering beams so as to offset dead load deflections, fabricators normally work to a figure
that is rather less than the full calculated simply supported deflection. However, the making of an explicit allowance for end restraint when conducting design calculations to estimate serviceability deflections is not normal practice.
