Experimental studies on pullout performance of anchor studs in high-performance concrete with hybrid steel fibers and synthetic fibers

Pullout performance of studs in high-performance hybrid fiber-reinforced concrete (HPHFRC) with varying proportions of steel fibers and TX12 synthetic fibers is investigated. A total of 24 unconfined anchor pullout tests were conducted, including eight scenarios of hybrid fiber combinations. The failure modes, ultimate tensile strength (Nu), and pullout load-displacement behavior of studs were analyzed. The incorporation of fibers significantly enhanced Nu and improved post-peak ductility. Hybrid fibers significantly enhance concrete performance compared to single fibers by improving crack resistance and creating a bridging network, leading to greater ultimate tensile strength, ductility, and toughness. Increased fiber content enlarges the bearing area, inducing an edge effect. This alters failure modes and anchorage performance, requiring greater clear distances to prevent radial cracking or splitting failure. A modified predictive model for Nu in HPHFRC is proposed, considering the influence of different fiber types. Compared to existing models, the proposed model demonstrated superior agreement with experimental data.