Structural performance of composite beams: effects of continuity and slenderness ratio

Abstract An experimental study was conducted to investigate the performance of both simply supported and continuous steel beams acting compositely with reinforced concrete slabs using profiled steel sheeting and shear connectors. The study tested six steel–concrete composite beams with monosymmetric steel sections attached to 100-mm concrete slabs. All slabs were reinforced using mid-depth steel mesh. The six tested beams were detailed as follows: (a) Three simply supported beams with span 2.90 m were tested for comparison and to evaluate the steel section’s shear capacity on behavior and failure modes of composite beams, and (b) three continuous beams with two spans were tested to evaluate the impact of beam continuity and the span-to-span ratio on structural performance and failure modes of composite beams. Experimental results show that reducing steel I-beam web height — thereby decreasing shear capacity — promotes brittle failure in concrete slabs of simply supported composite beams. The research further establishes a direct correlation between beam slenderness (quantified by L/ r ₛ ratio) and effective composite width. The transition from simple to continuous beam system produced several notable effects such as reduction in effective composite width, fundamental change in failure mode from brittle shear to ductile flexural mechanisms, and 20% reduction in composite section moment of inertia. Increase in span-to-span ratio yielded reductions in composite efficiency. The reduction in stiffness of continuous composite beams across all loading stages verifies the reduction of composite action with increasing span-to-span ratio.