Abstract Previous studies on steel frames cannot consider the effect of concrete slabs on the collapse behavior of structures, while recent experimental studies on steel-concrete composite frames fail to fully mobilize the tensile membrane action in slabs and catenary action in beams which have great influence on the failure mode of the frame. Large-scale experiments are conducted in this study on steel frames with flat concrete slabs to investigate the resistance mechanisms and typical failure modes of the structure. An edge-column removal scenario is used to consider a worse condition than an internal-column removal case. The resistance-vertical displacement relationship at the column-removal location, horizontal displacements at the structural edges and final failure patterns of main structural components are reported. Parametric studies are conducted using a validated numerical model to further quantify the effect of concrete slab thicknesses, reinforcement diameters, and beam section dimensions on the collapse resistance of composite structures. A simplified calculation method is also proposed to predict the resistance-displacement curve of composite framed structures under an edge-column loss scenario. The experimental results show that even without external horizontal restraints, tensile catenary action and membrane action can significantly develop in the steel beams and concrete slabs, respectively, at large deflections of structures under an edge-column loss scenario. Positive yield lines are found to distribute diagonally in the slab extending from the column-removal location to the two corners of the slab, while negative yield lines elliptically distribute along the edges of the slab. The numerical results highlight that the contribution of tensile membrane action in concrete slabs to the collapse resistance is less significant than that of catenary action in steel beams. Moreover, increasing the section height of beams guarantees a greater plastic bearing capacity of composite structures, but it fails to always provide a larger ultimate bearing capacity due to a poorer ductility.