Size Effect in Shear for Steel Fiber-Reinforced Concrete Members without Stirrups

At the member scale, very few previous tests reported for shear-critical steel fiber-reinforced concrete (SFRC) members have examined specimens with depths greater than 300 mm (11.8 in.), preventing a detailed assessment of the so-called size effect in shear for SFRC. This paper reports on laboratory results of 12 SFRC specimens with an overall height from 308 to 1000 mm (12.1 to 39.4 in.), and a constant shear span-effective depth ratio of 3. Specimens contained normal or high-strength SFRC with 1% volume fraction of hooked-end steel fibers and different longitudinal reinforcement patios, but no stirrups. The test results show that the steel fibers increase the shear capacity relative to geometrically similar reinforced plain concrete members. The normalized shear stress at, failure, however, was observed to decrease as the member depth increased, indicating that a size effect in shear occurs in SFRC members without stirrups. Modifications to the ACI 318-11 provisions for shear in SFRC members are proposed.