The International Information Center for Structural Engineers

On the interaction of partial interaction and shrinkage in composite steel-concrete t-beams

M. A. Bradford.
Book Title or Journal
Procedia Engineering
Number of pages
pages 396-401
The use of composite beams of steel and concrete joined by shear connectors goes back well over half a century, and they are now ubiquitous civil engineering structures. Their populaarity and efficiency derive from the fact that the concrete carries compression and the steel carries tension, thereby making best use of the two materials to enhance the strength and stiffness of the beam when the concrete slab is joined mechanically to the steel girder. Without considering long-term shrinkage and creep effects in the concrete, Newmark, Siess and Viest deriived the classic partial interaction solution in 1951, quantifying the increase in beam's stiffness as the stiffness of the mechanical shear connection increases; the solution being represented with hyperbolic trigonometric functions. With no shear connection between the concrete and steel, the deflection of the beam is based on the flexural stiffness of the two materials alone and any uniform shrinkage deformations of the slab will have no effect on the lateral deflection of the beam. On the other hand, if the shear connection between tthe concrete and steel is infinitely stiff, uniform shrinkage of the slab whose lever arm is eccentric the centroid of the transformed cross-section may lead to considerable shrinkage-based deformations, thereby negating the stiffening effects of the fully-composite action. In theory, a fully-composite beam may deflect more than one without any composite action because of shrinkage-based slab deformations. Using a rational technique based on virtual work, the paper presents a solution for a composite beam with elastic shear connection subjected to slab shrinkage deformations. Its focus is on identifying the competing and coupled influences of stiff partial interaction in reducing deformations, and high shrinkage deformations in causing beam deformations. The solutions may be used to optimise beam deformations, being suitable for deesign.