Influence of fiber orientation on the behavior of fiber reinforced concrete slabs

After several decades of research studies, design rules for fiber reinforced concrete (FRC) are now available for several structural elements. Starting from standard tests, it is possible to determine design parameters and constitutive laws to perform simplified sectional verifications and/or numerical analyses. However, one of the main issues still open is represented by the fiber orientation in the real structure that could be different from the one present in standard tests. For this reason, building codes take into account orientation factors to modify the standard material properties. The present paper aims to shed some new lights on the effects of the orientation of steel and macro-synthetic fibers on the local variability of FRC residual strength properties in slabs made with two concretes: Vibrated (slump of 80 ± 20 mm, V-FRC) and self-compacting concrete (slump flow diameter of 700 ± 50 mm, SC-FRC). In V-FRC slabs, the orientation of polymer fibers was more influenced by pouring and compaction process compared to steel ones. In SC-FRC slabs, the flow and wall effects resulted more significant when long steel fibers were used. The post-cracking performances locally determined in different points of slabs were compared against the ones obtained on standard beams as well. Finally, the global response of these slabs was numerically studied by considering two different support configurations: simply-supported slabs and slabs on grade.