Avaliação da diferença de resistência à punição sob a metodologia da ABNT NBR 6118:2023 e do Eurocode 2 (2023)

Abstract

This study focuses on the analysis of punching shear resistance in flat reinforced concrete slabs, comparing the design criteria established by ABNT NBR 6118:2023 and Eurocode 2:2023. Punching is a critical phenomenon in structural design, characterized by a brittle and localized failure at the slab-column interface, which can compromise the overall stability of the structure. Although flat slabs offer architectural and economic advantages, they are especially vulnerable to this type of failure, requiring rigorous attention during the design process.The analyzed standards present distinct approaches: ABNT NBR 6118 adopts an empirical formulation based primarily on concrete compressive strength, while Eurocode 2 uses a mechanical approach grounded in the Critical Shear Crack Theory (CSCT), as proposed by Muttoni. To evaluate the impact of these methodological differences on structural performance, a case study was conducted based on the model proposed by Santos (2018) and extended by Silva (2022), using computational modeling in the TQS® software. The analyzed structure consists of square slabs with varying thicknesses (20, 30, and 40 cm), subjected to three levels of live load (1.5, 3.0, and 6.0 kN/m²). Nine structural models were defined, and the internal forces and reinforcement ratios were obtained from the TQS® simulations. Punching shear verification was performed according to each standard?s criteria, considering their respective critical control surfaces.The results show significant differences in the ratios between punching shear resistance and applied shear stress. While ABNT NBR 6118:2023 yielded higher resistance-to demand ratios, often eliminating the need for punching reinforcement, Eurocode 2 required reinforcement in all evaluated cases, indicating a more conservative approach. The percentage difference between the standards' resistance-to-demand ratios exceeded 10% across all models, influenced by slab thickness, load level, and each standard's methodological basis.It is concluded that both standards are effective but adopt different design philosophies: the Brazilian standard is more flexible, while the European standard is more conservative, imposing additional safety margins. [resumo fornecido pelo autor]