Creep and shear-lag coupling in steel-concrete composite beams

ABSTRACT Under the assumption of linear viscoelastic behaviour for the concrete slab and linear elastic behaviour for the steel beam, a model for analysing the shear lag effect in steel-concrete composite beams, is proposed. By supposing that the slab loss of planarity is described by a fixed warping function, the vertical and longitudinal displacements of the generic cross section and the intensity of the warping (shear lag function) are assumed as unknowns of the problem. Integrating by parts the global balance condition obtained by the virtual work principle, three linear integral differential equations (expressing local equilibrium) with the relevant boundary conditions are obtained. Such a system is numerically solved by a step-by-step procedure combined with the finite differences method. Some applications on beams subjected to static actions show the practical uncoupling between creep and shear lag.