Evaluation du coefficient d'orientation dans les betons renforces de fibres metalliques

Ultra high performance fiber reinforced concrete's (UHPFRC) offer exceptional mechanical properties and durability. However difficulties predicting the uniaxial tensile performance and the high cost limit its use in the construction industry. Fiber orientation, density and distribution can each influence its mechanical behavior. The goal of the research work presented in this Master's Thesis is to propose a methodology to predict the flexural behavior of UHPFRC beams considering only the fiber orientation factor.;First, an image processing program was developed on MatlabRTM. The program automatically determines the fiber quantity, distribution, and orientation within a concrete section.;Then an initial experimental phase of uniaxial tensile tests with different fiber orientations was performed. The fiber orientation within the tensile specimens was controlled using inclined separators during casting. The uniaxial tensile tests showed that depending on the fiber orientation, the tensile strength can range from 4,5 MPa to 12MPa and the length of hardening behavior can be reduced up to 95%. The results indicate that fiber orientation is the dominant factor affecting the UHPFRC tensile behavior. A direct tensile law for different fiber orientation factors was then developed empirically from this experimental phase.;A second experimental phase on beams in flexure was performed to study the local effects of forms and steel reinforcement on the fiber orientation factor. Core samples of reinforced and unreinforced beams demonstrated that the reinforcement bar and the forms do not affect the fiber orientation. Furthermore, the bending tests were used to validate finite element models where the tensile behavior of the UHPFRC was determined using the measured fiber orientation factor and the empirical formulas developed in the first experimental phase.;The finite element models reproduced the tensile behavior well. The models confirmed that using an average orientation factor is sufficient to predict the flexural capacity of UHFRC beams with 96% accuracy.