Collapse resistance of steel beam-concrete slab composite substructures subjected to middle column loss

Abstract

An energy-based method is proposed to determine the structural responses of composite beam-slab substructures under middle column removal scenarios. A tri-linear resistance-displacement curve is proposed. Three factors contributing to the internal energy dissipation are accounted for, including the extension of reinforcing bars and steel beams, the additional bending moment induced from membrane forces in the slab and tensile forces in beams, and sectional bending moment along yield lines of the slab. Parametric studies are conducted based on validated finite element models to investigate the effect of slab planar aspect ratio, slab thickness, slab reinforcement ratio and beam section height on the behavior of composite beam-slab substructures subjected to middle column loss. The numerical results show that these four parameters have limited effects on the yield displacement of the substructure. The accuracy and effectiveness of the proposed method are verified against numerical results with errors less than 15%. It is found that the first two factors considerably contributed to the collapse resistance of the substructures at large deflections, by accounting for more than 65% of the total energy dissipation capacity. At the collapse limit state, the contribution from the slab is mainly influenced by its reinforcement ratio. The beam height has little effect on the beam contribution to the collapse resistance of the substructure.