REINFORCED CONCRETE FLAT SLABS: REVIEW OF STRUCTURAL PERFORMANCE, PUNCHING SHEAR BEHAVIOUR, AND DESIGN PROVISIONS

In buildings, flat slabs reinforced directly on columns without beams are still preferred floor system, as they do not require additional storey height, make formwork easier, and allow designers to be more flexible in floor planning. However, the lack of beams does focus the transfer of shear and moments on a small area around each column, so that the resulting punching failure is abrupt and with little warning. This paper synthesizes the published understanding of structural performance of the flat slab system under gravity and lateral loads, the mechanics and governing parameters of punching shear, and how the published understanding is reflected in the specific design provisions in the various design documents (ACI 318-19, Eurocode 2 and fib Model Code 2010). The procedure for an interior column is explained by giving a worked example. The review demonstrates the differences between codes only in the treatment of size effect, flexural reinforcement, and slab rotation, and that Critical Shear Crack Theory, which is depended on rotation, provides most physically consistent explanations of test results. Open questions are pointed out, such as the answer to the problem of the response of slabs under combined gravity and cyclic drift, the post-punching robustness, openings near the columns, and use of recycled or fibre-reinforced concretes