Splitting of concrete cover in steel fiber reinforced concrete: Semi-empirical modeling and minimum confinement requirements

The use of steel fiber reinforced concrete (SFRC) is becoming more and more common. Concerning bond of rebars to concrete, fibers provide passive confinement and not only improve bond performance but also affect the mode of bond failure. To analyze these aspects, a series of prismatic specimens have been subjected to the Pull Out Test, and an accurate model for predicting the mode of bond failure has been developed. The following factors have been considered: concrete compressive strength (30-50 MPa), rebar diameter (8-20 mm), concrete cover (between 30 mm and 5 times rebar diameter), fiber content (up to 70 kg/m3), and fiber slenderness and length. This model relates splitting probability to the factors considered. It has been proved that increasing fiber content restrains the risk of splitting failure. The favorable effect of fibers when preventing splitting failures has been revealed to be more important for higher concrete compressive strength values, which require higher concrete cover/diameter ratios for splitting failure to be prevented. Fiber slenderness and fiber length modify the effect of fiber content on splitting probability and therefore on minimum cover/diameter ratios required to prevent splitting failures.