Shear Strength and Moment-Shear Interaction in Steel-Concrete Composite Beams

Steel-concrete composite beams are currently designed against shear by neglecting the contributions of the concrete slab and composite action, while the moment-shear interaction is not addressed in current structural codes of practice. This paper presents an experimental and numerical study on the shear strength and moment-shear interaction in simply-supported steel-concrete composite beams. Fourteen composite beams and one steel beam were tested under combined bending and shear. The effects of partial shear connection and shear reinforcement in the slab were also studied. A nonlinear finite element model was developed and found capable of accurately predicting the behavior of the composite beams. Extensive parametric studies were then conducted using the validated numerical model. The results allowed for the derivation of a moment-shear interaction law for composite beams and highlighted the high degree of conservatism in current structural specifications. It is shown that both the concrete slab and the composite action contribute significantly to the shear strength of a composite section and that the main factors that influence the shear capacity of a composite beam are the slab thickness and the degree of shear connection. Based on the experimental and numerical results, a design model is proposed for a more efficient design of compact composite beams in regions where the acting shear is high.