Title: Rational Modelling of Shrinkage Gradients, Partial Interaction and Creep in Composite Beams

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Publication: CIA

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Date: 2/14/2011

Abstract:
Composite construction is characterised by three material models: those of concrete, steel and the shear connection. The structural behaviour of composite beams is influenced strongly by these three material components, and by their interaction. Deflections in composite beams are affected particularly by concrete long-term effects, and because of the preference for sacrificial steel deck formwork in lieu of flat plywood formwork, a condition of shrinkage gradient develops which can increase the beam deflections when compared with those with a bare flat slab concrete soffit. This paper presents a rational formulation used to model this common situation, based on the principle of virtual work. It arrives at a solution in closed form, for which the deflections (and stresses) in the composite beam are characterised by the creep coefficient, variation of shrinkage strain through the slab depth and the elastic stiffness of the shear connection, as would be obtained empirically from push tests. The solution is compared with finite element results reported elsewhere, and the accuracy is shown to be good. The solution allows for quantifying the beam behaviour in a form suitable for codification, and some illustrative examples are given to show the influence of various parameters on the deflections of composite T-beams.