Structural Behaviour of Flat Slab-Column Connections Under Punching Shear in Typical Nigerian Building Practice

Punching shear failure at flat slab-column connections represents one of the most critical and often sudden failure modes in reinforced concrete structures, yet its design and detailing receive insufficient attention in many Nigerian building projects. This study investigates the structural behaviour of flat slab-column connections under punching shear, focusing on the adequacy of design and detailing practices observed in residential and commercial building projects across Oyo State in the South West geopolitical zone. Twenty sets of structural drawings from recently constructed flat slab buildings were reviewed and evaluated against the punching shear provisions of Eurocode 2, including requirements for shear reinforcement, column strip reinforcement concentration, and edge condition detailing. Additionally, four full-scale slab-column connection specimens were fabricated and tested to failure under concentric loading in the Civil Engineering laboratory at a public university in the zone. Results from the drawing review indicate that shear reinforcement was specified in only three of the twenty sets of drawings, with the remainder relying solely on concrete tensile capacity despite column-slab load intensity ratios that exceeded the threshold requiring reinforcement in eleven cases. Experimental specimens without shear reinforcement failed at loads averaging 1.18 times the Eurocode 2 predicted capacity, reflecting partial conservatism in the code model for Nigerian concrete mixes. Specimens with proprietary shear stud reinforcement exhibited forty-two percent higher ultimate load and significantly improved post-peak ductility. The study advocates for mandatory punching shear design documentation as part of building plan approval submissions. Keywords: flat slab, punching shear, column connection, Eurocode 2, reinforced concrete.