Progressive collapse resistance of RC beam-slab substructure under two-adjacent-edge-columns removal scenario

Abstract

The progressive collapse resistance of reinforced concrete (RC) frame structures has attracted much attention following a series of catastrophic accidents of collapse in the history. Of the numerous studies conducted in the past, the majority devoted to single-column removal cases. However, more than one column may initially fail when the structures are subjected to accidental actions. Meanwhile, the peripheral edge-columns of the structures are most vulnerable to threats due to their accessibility to the public. To this end, this study aims to investigate the progressive collapse resistance of the RC frame structures after removing two-adjacent-edge-columns. First, a quasi-static push-down experiment was performed on an RC beam−slab substructure under the scenario of two-adjacent-edge-columns removal. The experimental results found that the resistance of the beam−slab substructure at the beam mechanism stage was mainly provided by the flexural action (FA) of the beams and slabs, as well as the compressive arching action (CAA) of the beams and the compressive membrane action (CMA) of the slabs along the edge direction. The resistance increased again after entering the catenary mechanism stage, which mainly benefited from the development of the catenary action (CTA) of the edge-beams and the tensile membrane action (TMA) of the slabs along the edge direction. Second, a validated numerical model was employed to further investigate the collapse-resistant mechanism of the substructure. The numerical results indicated that the contribution of the CTA in the edge-beams to the progressive collapse resistance was approximately 51 % at the ultimate state, which was greater than that of the TMA of the slabs. Thereafter, parametric studies were conducted to quantify the contribution of the slabs and the influence of the number of removed columns on the progressive collapse resistance of the substructure. It was found that the ultimate resistance of the beam−slab substructure was 61 % higher than that of the substructure without slab, and the equivalent uniform load that the substructure could resist in the case of two-adjacent-edge-columns removal was about two-thirds of that in the case of one edge-column removal. Finally, the first peak resistance of the RC beam−slab substructure was predicted using yield-line method, resulting in a conservative result because the CAA of the beams and the CMA of the slabs were not considered.