Tailoring SFRC to mechanical needs: Full-scale experiments with optimized hybrid SFRC composition and fiber alignment to stress path

Steel fiber reinforced concrete (SFRC) is widely used in structural applications due to its residual tensile strength, crack control and durability. Its performance can be optimized through two strategies: 1) positioning a higher-performance SFRC only in the zones of maximum stress and 2) orienting fibers to align with principal stress directions. This study introduces a novel optimization strategy to enhance SFRC structural elements: the above mentioned optimization is carried out through an innovative casting device and methodology that ensure directional control of fiber alignment, leveraging the material's anisotropic properties, and allow casting different SFRC materials in a monolithic structural element. The effectiveness of this approach is assessed through six full-scale plates subjected to concentrated loads, three with standard reinforcement solutions and three optimized SFRC specimens, including curved strips of high-performance SFRC with oriented fibers, following the tension isostatic lines. Results indicate that optimized SFRC specimens exhibit up to a threefold improvement in crack control with respect to traditional rebar reinforcement and a 40 % increase in bearing capacity as compared to traditional SFRC. Additionally, direct comparison of residual performance and fiber orientation – measured with an electromagnetic induction method – is carried out between standard beams (cast according to EN 14651) and beams cut from the tested plates, showing the effectiveness of the casting device in steering fiber orientation and suggesting a good correlation between performance and orientation.