Pullout response of inclined steel fibres under direct shear

Fibre-reinforced concrete (FRC) has been used as a structural material for many years, mainly in tunneling and industrial flooring. In recent years, new applications in which FRC can be partially or totally used in substitution of conventional steel reinforcement have appeared. Despite this, important issues regarding the behaviour and the design of FRC still have to be fully understood. For example, there is no direct analytical model universally accepted for design purposes to express and evaluate FRC behaviour under longitudinal shear. This paper therefore evaluates the response of single fibres under longitudinal shear to obtain information regarding the debonding and slipping behaviour of single fibres from the concrete matrix. Previous studies have been conducted with the fibres aligned with the load direction and perpendicular to the cracked plane. This arrangement however, is just one of an infinite number of possible arrangements that fibres could take up in any real application, where the fibres are likely to adopt a random distribution and orientation. Although models to predict the pullout response of fibres already exist (notwithstanding the inclination respect to the loading direction), these models were developed to model tensile behaviour. The objective of this study is therefore to propose a direct model to predict the pullout in shear of fibres embedded in a cementitious matrix. Therefore, one of the previous tensile models, is applied and extended to allow it to also describe the pullout behaviour of fibres under direct shear. This adapted model is compared with empirical data obtained from an existing experimental campaign on single fibres tested on direct shear. The results show a good agreement between the model and empirical data for displacements up to 10 mm, which represents an improvement in the capacity and accuracy of engineers to predict the behaviour of shear in FRC.