abstract: This paper proposes an adjusted function for estimating the punching shear load-carrying capacity of concrete flat slabs without shear reinforcement according to the Brazilian standard code. The Adjusted function considers the influence of the steel fiber content. Data from 68 steel fiber reinforced concrete slabs (SFRC slabs) were used, simulating the connection of flat slabs with square section columns. These slabs were obtained from a study conducted by 14 different researchers. The parameters used for the adjusted function were the fiber content and the compressive strength of the concrete. The adjusted function was obtained by curve-fitting. The result from the adjusted function shows a relation in the order of 1.3 between the experimental rupture load and the calculated load, a value close to that already obtained by the normative text when the calculation is for conventional concrete. This shows that the proposal presented here keeps the same level of security with a confidence index of 96% in comparison with other authors’ models presented in this study.

resumo: Este trabalho propõe uma função para estimar a capacidade de carga com ruptura na punção de lajes lisas de concreto sem armadura de cisalhamento de acordo com a norma brasileira. A função considera a influência do teor de fibra de aço na adição do concreto. Foram utilizados dados de 68 lajes de concreto armado com fibras de aço, simulando a ligação de lajes lisas com pilares de seção quadrada. Essas lajes foram obtidas a partir de um estudo realizado por 14 pesquisadores diferentes. Os parâmetros utilizados para a função foram o teor de fibras e a resistência à compressão do concreto. A função foi obtida por ajuste de curva. O resultado da função ajustada mostra uma relação da ordem de 1,3 entre a carga de ruptura experimental e a carga calculada, valor próximo ao já obtido pelo texto normativo quando o cálculo é para concreto convencional. Isso mostra que a proposta aqui apresentada mantém o mesmo nível de segurança com um índice de confiança de 96% em comparação com os modelos de outros autores apresentados neste estudo.

Vegetable fibres have been shown to be promising as reinforcement in composites because they are abundant, renewable, and low cost. However, the fibre-matrix interaction can be damaged by dimensional variation of vegetable fibres, due to moisture variations. The alkaline medium of cementitious matrix is aggressive to natural fibres, compromising their durability. The aim of this study was to modify sisal fibres (Agave sisalana) by esterification with acyl chlorides to improve their stability and compatibility with the cementitious matrix in order to optimize the performance and durability of composites. The esterified fibres were characterized by moisture absorption, tensile tests, Thermogravimetric Analysis (TGA), and Scanning Electron Microscopy (SEM) and the composites by bending tests and SEM. The results showed that esterification changed both the morphology and physical properties of sisal fibres. The composite produced using esterified fibres with octanoyl chloride maintained the properties of 28 to 90 days of age, which represented an improvement in the fibre stability compared to natural fibre composite.