Evaluation of orientation factors influencing the shear and flexural behavior of elements in steel fiber reinforced concrete

The structural design of Fiber Reinforced Concrete (FRC) elements should take into consideration fiber orientation since the residual properties of FRC strongly depend on the inclination between fibers and the crack plane. Designers must be aware of the possible negative influence of fiber orientation, but they may also take advantage of its positive effect. Current standards, such as the fib Model Code 2010, the German Committee for Structural Concrete DAfStb, and Annex L of the new Eurocode 2, introduce an orientation factor that should transform the mechanical properties determined from standard beams (EN 14651, ASTM 1609) into mechanical properties representative of the real structure. Unfortunately, there is still a lack of studies for a proper determination of the orientation factors for different structural elements. In this context, the present paper reports the results of an experimental program aimed at evaluating the influence of fiber orientation on the shear and flexural behavior of beams in steel fiber reinforced concrete (SFRC). Nine full-scale beams (410 cm long, 70 cm high and 15 cm wide) were cast using vibrated and self-compacting concrete, following the most common casting procedure adopted in practice. Thirty-six small specimens were extracted and tested from three full-scale beams to evaluate the local residual properties of SFRC, while the remaining six full-scale beams were tested under shear loading. Fiber density, orientation number at the cracking surface (assessed through image analysis), and tomography analysis were also evaluated. Based on the findings, orientation factors to be adopted in the structural design of SFRC elements are proposed for both shear and flexural design.