Finite Element Investigation of Reinforced Concrete Flat Slab-Column Connections under Static and Seismic Loading

Punching Shear failure is a severe Limit condition that controls the seismic behavior of Reinforced Concrete (RC) flat slab-column connections. Such critical structural connections are widely used in modern construction due to economic design benefits and aesthetic appearances, which reduce the floor height in the absence of beams. The study identifies the key parameters that influence flat slab column connection failures, including punching shear, inadequate reinforcement, and poor detailing. Previous studies have revealed that the punching shear failure is the primary cause of Flat slab column connection failures, strongly influenced by concrete grade and reinforcement detailing. This work is a Finite Element Analysis (FEA) exploration of twelve flat slab-column connection models in FEA software to assess the effect of concrete grades M25 and M30, utilizing different types of reinforcement, including stirrups and stud rails, and loading for both static and seismic conditions. Concrete Damaged Plasticity (CDP) was used to model the nonlinear material behaviour of concrete, and the seismic shear demand was applied as required by the IS 1893. Unstiffened flat slabs in the shear region were brittle and exhibited rapid post-peak strength that declined, resulting in low residual capacity. Conversely, a stiffened flat slab in the shear region has demonstrated significant improvements in mass-carrying capacity, ductility, and energy-dispersing capabilities. Stirrups increased confinement, and stud rails offered better stability at the post-peak by maintaining residual strength and increasing the time to evolve damage. A higher concrete grade increased stiffness and maximum resistance, whereas the type of reinforcement was a key factor in determining ductility. A relative comparison with IS 456, ACI 318, and Eurocode 2 design provisions revealed that the predictions of punching shear using these codes are always conservative compared to those obtained through numerical methods. In general, the results emphasize the significance of reinforcement detailing in increasing the seismic resilience of flat slab systems, with stud rails proving to be the most promising form of reinforcement.