Punching Shear in RC Flat Slabs: A Comprehensive Review on Mechanics, Design Challenges, and Progressive Collapse Resistance

Reinforced concrete (RC) flat slab systems are a preferred choice in modern construction due to their architectural and economic advantages. However, their structural integrity is critically challenged by punching shear, a brittle failure mechanism at slab-column connections that can precipitate catastrophic progressive collapses. This review synthesizes recent research to provide a comprehensive overview of the factors influencing punching shear, the efficacy of predictive models, the evolution of shear reinforcement, and innovative strengthening techniques. The analysis consolidates findings on failure mechanics, highlighting the dominant role of concrete's tensile properties and the complex influence of time-dependent phenomena like creep and shrinkage. It examines a wide array of parameters, including slab depth (size effect), flexural reinforcement ratios, the presence of openings, load eccentricity, complex geometries like edge and re-entrant corners, column rectangularity, non-rectangular column grids, and the use of posttensioning and non-traditional materials like Glass Fiber-Reinforced Polymer (GFRP) bars. A critical assessment of design code provisions (e.g., ACI 318, Eurocode 2) against advanced numerical methods and new proposed standards (FprEN 1992, MC 2010) reveals significant limitations in current codes, particularly for slabs with low reinforcement ratios (flexure-driven punching), significant depth, or non-standard geometries. The review delves into the nuances of shear reinforcement, emphasizing how stirrup detailing—anchorage, inclination, and configuration—profoundly impacts structural performance. A significant focus is placed on the role of Nonlinear Finite Element Analysis (NLFEA), detailing the importance of model calibration and the capabilities of tools like the Concrete Damaged Plasticity (CDP) model, with particular attention to the influence of the dilatancy angle. Lessons from real-world building collapses underscore the imperative of integrating construction-phase analysis and robust design to prevent progressive collapse. Finally, the paper outlines key challenges and charts a course for future research to enhance the safety and resilience of flat slab structures.