Punching Shear Behaviour of Reinforced Concrete Flat Slabs with Openings: Mechanisms, Failures, and Strengthening Strategies: A Review
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Abstract
Reinforced concrete flat slabs are widely used for their architectural flexibility and construction efficiency, but they are vulnerable to punching shear failure—a sudden collapse at slab-column connections. Openings for stairs, elevators, and utility ducts worsen this vulnerability by removing concrete and reinforcement from critical regions.
This review synthesized studies from 2007 to 2025 to evaluate punching shear behavior in slabs with openings and the effectiveness of strengthening techniques. Findings showed that openings adjacent to columns reduced punching shear capacity by 29% to 65%, with circular openings causing less damage than rectangular ones. Openings beyond four times the slab thickness had minimal effect.
Strengthening methods proved highly effective. Externally bonded CFRP sheets restored or enhanced capacity by 22% to 77%. ECC applied around columns increased punching capacity by 34% to 38% and transformed failure from brittle to ductile. Super elastic Shape Memory Alloy (SMA) stirrups improved energy absorption by over 100%. Sustainable alternatives like geopolymer concrete with CFRP strengthening achieved up to 77% capacity improvement, while basalt-FRP bars reached 89% of steel-reinforced slab strength.
Traditional design codes like ACI 318 were overly conservative, whereas Artificial Neural Network models provided more accurate predictions with only 9% average error.
This review confirms that while openings severely weaken flat slabs, modern strengthening techniques effectively restore performance.
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