In the study, the effects of using ultra‐high‐performance fiber reinforced concrete (UHPFRC) on deflection and curvature ductilities, moment capacities, flexural stiffness, and cracking behaviors of beams were experimentally investigated. Eight singly reinforced beams with four tensile reinforcement ratios (0.009, 0.019, 0.028, and 0.043) were tested under four‐point loading to create a pure moment behavior in the mid region. The evaluations were made by comparing the UHPFRC beams and non‐fiber beams containing UHPFRC matrix without steel fiber. Straight micro‐steel fibers with volumetric ratio of 1.5% were used in the UHPFRC matrix. The results of study indicate that the use of UHPFRC for beams having especially high reinforcement ratios provides significant advantages in terms of the considered parameters. Especially high compressive strength and deformation capacity of the UHPFRC allow the use of high reinforcement ratios in beams which results in more economical sizes as long as the beam deflections ensure for both the serviceability and the ultimate limit states. In this study, however, the simplified numerical approach developed for the flexural design of fiber reinforced concrete was applied to the UHPFRC beams, as well.

No abstract

In this study, the effects of different fiber types on shear behavior (cracking pattern, shear cracking strength, ultimate shear strength, and post-cracking deformability) of ultrahigh-performance fiber-reinforced concrete beams were investigated experimentally. For this purpose, 15 ultrahigh-performance fiber-reinforced concrete beams including different steel fiber types (two straight, two hooked, and one double hooked) with three volume fractions (0.5%, 1.0%, and 1.5%) were casted without shear reinforcement and tested under four-point loading until the failure. In addition to the experimental program, three existing numerical models proposed for the shear capacity of fiber-reinforced concrete beams were investigated to show the applicability of these models to the ultrahigh-performance fiber-reinforced concrete beams. The experimental results demonstrated that the straight fiber of 13 mm is the most effective fiber type in terms of the considered parameters. However, the addition of 13-mm straight fiber with 1.5% by volume into the ultrahigh-performance fiber-reinforced concrete beam changed the failure mode from the shear to flexure without shear reinforcement.

ÖzetBu çalışmada, Ultra Yüksek Dayanımlı Beton'un (UYDB)

In the presented paper, the effectiveness of steel fiber use on the shear and flexure behaviors of ultra-high performance concrete (UHPC) beams and the feasibility of steel fibers in place of shear reinforcement were investigated experimentally. In this framework, a total of four I-shaped UHPC beams were produced for a high tensile reinforcement ratio of 2.2%. While two of them were non-fiber UHPC beams with and without the shear reinforcement to show the contribution of steel fibers, the remaining beams were made from the ultra-high performance steel fiber-reinforced concrete (UHP-FRC) having the short straight fibers with 1.5% and 2.5% by volume. The shear and flexural parameters, such as the load–deflection response, cracking pattern, failure mode, deflection, and curvature ductilities were discussed based on the four-point loading test results. While the reference beam without fiber and shear reinforcement failed by the shear with a sudden load drop before the yielding of reinforcement and produced no deflection capability, the inclusion of steel fibers to the UHPC matrix transformed the failure mode from shear to flexure through the fibers’ crack-bridging ability. It might be deduced that the moderate level of steel fiber use in the UHP-FRC beams may take the place of shear reinforcement in practical applications.