Comparative Study of Drop Panels, Stirrups, and Stud Rails for Enhancing Punching Shear Resistance under Seismic Actions

Abstract

Problems with punching shear failure at slab-column joints have remained one of the major problems in RC flat slabs, especially where there is a combination of loadings from both gravity and lateral forces acting on the slab. This paper presents a numerical study of the use of drop panels and shear reinforcements in improving slab-column joints using nonlinear FEM with the CDP approach. Ten models (C25-C34) were considered while considering the two grades of concrete (M35 and M40), three types of reinforcement systems (unreinforced, with stirrups, and with stud rails) under static and Lateral loading conditions. The numerical results suggest that drop panels increase initial stiffness and Peak lateral load (for seismic analyses) capacity of slab–column joints. But, without geometric enhancement, the brittle punching behaviour under Lateral loading could not be prevented. The unstiffened configurations showed substantial loss of strength and higher deformations. Stirrups had been introduced to provide better confinement and post-peak stability. The systems with stud rail reinforcement had the best numerical response when measured in terms of load-carrying capacity, residual strength and ductility. The presence of a stirrup gives the added advantage of increased lateral load capacity of about 330% as well as good post-peak behaviour. The stud rail system exhibits the best overall behaviour, where the lateral load capacity can be increased by about 400%. The grade effect of concrete reveals that more the strength, the higher the stiffness and capacity and the lower the ductility in non-reinforced applications. The sensitivity analysis proves that the most important parameter that controls the performance is the shear reinforcement type. A comparison with codal provisions such as IS 456, ACI 318, and Eurocode 2 indicates that the existing formulations do not adequately capture the effect of reinforcement and the post-peak structural behaviour. The numerical results indicate that, out of all the examined configurations, the use of both drop panels and stud-rail reinforcement would yield the most favourable structural response. These results, however, are based on finite element simulation and require experimental validation in the future.