New testing approach for extracting the shear friction material properties of ultra-high-performance fiber-reinforced concrete

Shear friction (SF) theory governs the relationship between the stresses and displacements that occur due to sliding along a concrete-to-concrete interface subjected to varying degrees of lateral confinement. This theory is commonly applied to predict the transverse shear strength of reinforced concrete beams and slabs, the longitudinal shear capacity and behavior of precast connections, the size effect and confinement in compression members, and flexural failure in the compression region flexural members. The SF material properties required for this theory are commonly determined from tests where the confining force across the sliding plane is passively induced through transverse reinforcement and therefore difficult to quantify and isolate from the reinforcement dowel action. In this paper, a new test apparatus is presented to determine the SF properties of ultra-high-performance fiber-reinforced concrete (UHPFRC). The proposed setup has the following benefits: it removes the need for passive reinforcement by applying a normal stress hydraulically, thereby allowing confinement to be directly measured and controlled; it removes the effect of dowel action; and it allows the use of specimens manufactured from 200 × 100-mm cylinders, which is beneficial because they can be cored from larger specimens to investigate the influence of fiber orientation. To verify this new apparatus, a series of 16 tests were conducted on UHPFRC with a range of short straight and long hooked steel fibers as well as a range of normal confining stresses.