Influence of embedment length on the pullout behavior of steel fibers from ultra-high-performance concrete

Single fiber pullout behavior has been investigated extensively at various embedment lengths, and to generalize the test results of the existing studies, the implication of embedment length on the pullout behavior needs to be analyzed. To this end, experiments were conducted with two types of steel fibers in ultra-high-performance concrete (UHPC) at three embedment lengths and two inclination angles. The effect of embedment length on the pullout behavior was more significant in the half-hooked fiber than the straight one. Its pullout performance was also better than that of the straight fiber up to an embedment length of 10 mm; however, the effectiveness decreased with an increase in the embedment length. At the longest embedment length of 15 mm, the pullout energy and equivalent bond strength obtained for the half-hooked fiber samples were poorer than those obtained for the straight fibers. Therefore, its maximum length is suggested to be below 30 mm at a diameter of 0.375 mm to prevent premature rupture in UHPC.