Effect of Different Steel Fiber Type and Content in Flexural Behavior of Ultra High Performance Fiber Reinforced Concrete

In the research study, the effect of different fiber contents to flexural behavior of the Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) was investigated experimentally. Various prismatic beam specimens with a dimension of 100×100×400 mm including two types of end-hooked steel fibers (aspect ratios: 30/0.55 and 60/0.75) in macro forms and one short straight steel fiber (aspect ratio: 13/0.16) in micro form were produced. The beam specimens corresponding to a total of 18 mixtures having two different volume fractions (1% and 1.5%) were subjected to series of four-point bending tests in accordance with the ASTM standard C 1609. The experimental test results were discussed in terms of the cracking patterns, flexural strengths and toughness (energy absorption ability). In addition, a parametric research was conducted to ensure an appropriate homogenous UHPFRC mixture as well as good workability for the steel fiber volume fraction of 1.0%. Hence the prism and cubic samples were produced by modified of the composition of matrix mixtures (i.e. aggregate, water/binder, cement, superplasticizer). The performance of mixtures was evaluated in terms of the slump flow, T 500, compressive strength and workability. It is apparent from the test results, the use of micro steel fiber significantly improves the flexural performance of the UHPFRC comparing to that of the macro form. It was also noted that the fiber type is decisive in characteristic of the load- deflection curve while the volume content amplifies it with an increasing trend after the first cracking region. When evaluating all UHPFRC matrixes, some of the mixtures under consideration ensured good fiber distribution, workability as well as target compressive strength

Investigation of Parameters Affecting the Equivalent Yield Curvature of Reinforced Concrete Columns

In this study, the response quantities affecting the equivalent yield curvature, which is important in the deformation-based seismic design and assessment of structural systems, are investigated for reinforced concrete columns with a square cross-section. In this context, the equivalent yield curvatures were determined by conducting moment–curvature analyses on various column models, in which the axial load level, cross-section dimension, longitudinal reinforcement ratio, and concrete compression strength were changed parametrically, and the independent and/or combined effects of the relevant parameters were discussed. Depending on the axial load levels of P/Agfc′ < 0.3, P/Agfc′ = 0.3, and P/Agfc′ > 0.3 for the considered columns, the yielding of reinforcement, yielding of reinforcement and/or concrete crushing, and concrete crushing governed the yield conditions, respectively. It can be noted that the cross-section dimension and axial load level became the primary parameters. Even though the independent effects with regard to particular parameters remained at minimal levels, the combined effects of them with the axial load became important in terms of the equivalent yield curvature

Steel Fiber Use as Shear Reinforcement on I-Shaped UHP-FRC Beams

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