The influence of the steel beam‐concrete slab interaction on the robustness capacity of steel frames

Seismic resistant multistorey steel frames are expected to mitigate progressive collapse even when subjected to extreme loading events. The use of high redundant structural systems and ductile members and connections are key features that provide such structural robustness. The composite action between the steel beam and the concrete slab may also help increasing the robustness, but in practice it is difficult to quantify this contribution if the joint behaviour is not detailed. The paper presents the results of a numerical study that aimed to investigate the contribution of the composite action to the progressive collapse resistance of steel frame structures. The main parameters investigated in the study were the level of the composite action in beams and strength and stiffness properties of beam‐to‐column joints. The numerical model was calibrated using two reference experimental column loss tests, one with steel beams and one with composite beams. The model considers the interaction between the steel beams and concrete slab by means of shear studs and reinforcement detailing. The results showed that the contribution of the slab lessens the demands on the joints when compared with bare steel systems and provides and adequate behaviour at large deformation stage. The progressive collapse resistance may be further controlled by means of joint flexural and axial strengths.