Load-Resistant Mechanism and Failure Behaviour of RC Flat Plate Slab-Column Joints Under Concentric and Eccentric Loading

Progressive collapse, usually caused by accidental or abnormal loading, is a structural failure disproportionate to its original cause. Reinforced concrete (RC) flat plate structures are vulnerable to brittle punching shear failure in the vicinity of slab-column joints, which may initiate disastrous progressive collapse causing significant economic, social, and psychological consequences. This paper presents a series of experimental investigations of twenty-one 1/3-scaled slab-column joint specimens with in-plane restraints, under opposite punching shear directions, and subject to concentric and eccentric loading conditions. Three design parameters (slab thickness, reinforcement ratio, and flexural reinforcement extension) and three strengthening methods (embedded beams, stirrups in punching area, and ring beams) were considered. The load-resisting and deformation capacities of the joints, as well as their punching shear and post-punching failure behaviours were examined in detail. In addition to the experimental studies, numerical modelling techniques were also developed to simulate the physical tests with emphasis on their load-displacement responses, punching shear and post-punching capacities and crack development. Results demonstrate that (1) the punching shear capacity is mainly governed by the geometrical dimensions of the slab; (2) the post-punching strength is primarily regulated by the integrity rebars going through the column. The continuous integrity rebars are imperative for activating tensile membrane action thereby enhancing post-punching capacity in progressive collapse events.