Issue 31

A. Abrishambaf et alii, Frattura ed Integrità Strutturale, 31 (2015) 38-53; DOI: 10.3221/IGF-ESIS.31.04 38 The influence of fibre orientation on the post-cracking tensile behaviour of steel fibre reinforced self-compacting concrete A. Abrishambaf, V.M.C.F. Cunha, J.A.O. Barros ISISE, Dep. Civil Eng., School Eng., University of Minho, Campus de Azurém 4800-058 Guimarães, Portugal. vcunha@civil.uminho.pt A BSTRACT . Adding fibres to concrete provides several advantages, especially in terms of controlling the crack opening width and propagation after the cracking onset. However, distribution and orientation of the fibres toward the active crack plane are significantly important in order to maximize its benefits. Therefore, in this study, the effect of the fibre distribution and orientation on the post-cracking tensile behaviour of the steel fibre reinforced self-compacting concrete (SFRSCC) specimens is investigated. For this purpose, several cores were extracted from distinct locations of a panel and were subjected to indirect (splitting) and direct tensile tests. The local stress-crack opening relationship ( σ-w ) was obtained by modelling the splitting tensile test under the finite element framework and by performing an Inverse Analysis (IA) procedure. Afterwards the σ-w law obtained from IA is then compared with the one ascertained directly from the uniaxial tensile tests. Finally, the fibre distribution/orientation parameters were determined adopting an image analysis technique. K EYWORDS . Fibre dispersion and orientation; Self-compacting concrete; Tensile behaviour; Splitting tensile test; Inverse analysis. I NTRODUCTION dding fibres to concrete provides several advantages, especially in terms of controlling the crack opening width and propagation, increasing the energy absorption capacity, as well as increasing the post-cracking tensile strength [1, 2]. In composites reinforced with low fibre contents, the contribution of the fibres mainly arises after the crack initiation. Crack opening in steel fibre reinforced concrete (SFRC) is restrained by the bond stresses that develop at the fibre / matrix interface during the fibre pull-out. Moreover, one of the most important properties of SFRC is its ability to transfer stresses across a cracked section rather uniformly, which depends on the fibre reinforcement effectiveness, i.e. fibre properties (their strength, bond and stiffness), and fibre distribution/orientation towards the active crack plane [3]. In order to optimize the fibre contribution to the post-cracking behaviour, it is important to enhance the distribution and orientation of the fibres at the crack plane. Since, fibres are more effective fairly aligned along the principal tensile stresses directions [4, 5]. The dispersion and orientation of fibres in the SFRC bulk hardened-state results from a series of stages, namely [6]: fresh-state properties after mixing; casting conditions into the formwork; flowability properties; and wall-effect introduced by the formwork. Among the aforementioned parameters, flowability of steel fibre reinforced self-compacting concrete (SFRSCC) is the most important one [7-9]. Having in mind that distribution/orientation of the fibres influences significantly the mechanical properties of the SFRSCC, it is important to control and consider both parameters, especially in terms of the design applications. A