Impact Loading of Circular Slabs Using Curvilinear Shear Reinforcement Under Different Support Conditions

Abstract The impact resistance and punching behavior of circular reinforced concrete slabs are critical for structures subjected to localized dynamic loading. This study experimentally investigates the failure mechanisms and punching capacity of circular slabs incorporating W-bent shear reinforcement and steel fibre reinforced concrete (SFRC) under repeated drop-weight impact loading. Circular slabs with diameters of 450 mm, 600 mm, and 750 mm were tested under simply supported and fixed boundary conditions to evaluate the influence of slab geometry, support restraint, and fibre reinforcement on impact performance. The experimental observations revealed that slab failure was governed by a combination of radial and circumferential cracking, flexural tensile stress development, and localized punching shear beneath the impact zone. Conventional concrete slabs exhibited brittle behavior characterized by wide radial cracks and pronounced punching cone formation. SFRC slabs demonstrated delayed crack initiation, distributed crack propagation, and reduced fragmentation due to the fibre bridging mechanism. The incorporation of W-bent shear reinforcement further enhanced the shear transfer capacity and restricted the propagation of inclined punching cracks. An impact energy balance approach was adopted to evaluate the energy absorption capacity of the slabs between the initial cracking and final failure stages. The results showed that increasing slab diameter, the presence of steel fibres, and fixed boundary conditions significantly improved the energy dissipation capacity and crack resistance ratio of the slabs. Based on the experimental findings, an energy-based analytical model was proposed to predict the punching capacity of circular slabs, incorporating the effects of energy dissipation, crack resistance, slab diameter, and boundary conditions. The proposed model demonstrated good agreement with the experimental trends. The results confirm that the combined use of steel fibres and W-bent shear reinforcement significantly enhances the impact resistance and punching capacity of circular slabs, making them suitable for structures exposed to severe dynamic or impact loading conditions.