Precast steel-fiber reinforced concrete (SFRC) on beams: Results from an experimental campaign

An experimental campaign on the use of steel fibers in reinforced concrete elements is developed to evaluate improvements in the mechanical properties of precast members. Distributed steel fibers can also enhance the production chain by reducing the assembling time of the standard reinforcements, especially stirrups. Indeed the production of stirrups requires a first post-processing for their forming and cutting and additional time for assembling phase. An optimization of the stirups amount in the production chain of precarst reinforced concrete (RC) elements can be useful. The experimental investigation is carried out both on the material scale and on the structural scale of small elements in 1:2-1:5 scale. First of all, a pilot campaign was carried out on the material scale with a different amount of steel fibers (20 kg/m3-Vf = 0.25 %; 30 kg/m3 Vf = 0.38 % and 40 kg/m3-Vf = 0.50 %) of fiber types 3D65/40GG and 3D80/60GG: the aim is to achieve the ideal percentage to be used without changing the original mix design. An appropriate set of beam specimens have been constructed with assigned content of steel fibers (40 kg/m3-Vf = 0.50 %) and traditional reinforcement such to achieve both shear and bending failure. A FEM analysis is calibrated to reproduce the results of tests. The bending and shear capacity of fiber-reinforced concrete beams are compared to traditional ones. The results are discussed by comparing Italian with German standards and considering Model Code 2010 highlighting significant difference among these standards. The results showed that the use of steel fiber in RC precast elements produced an increase of shear strenght greater than indicated by actual standards. Moreover the addition of fibers can modify the jerarchy of shear-bending failure. Finally, some design remarks, based on experimental evidence, are proposed to help designers and producers of precast RC elements to implement the present results in their precasted manufacts.