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This study evaluated the shear strength of a diagonally reinforced coupling beam with steel fibers subjected to cyclic loading through experiments. A total of seven specimens were examined using the amount of transverse reinforcement, concrete strength, and volume fraction of steel fiber as variables. The experiments showed that sufficient ductility and strength were ensured even when steel fibers were incorporated and transverse reinforcement was simplified. In particular, with a 2% volume fraction of steel fibers, the strength and ductility satisfied ACI 318-19 because steel fiber-reinforced concrete sufficiently replaced the transverse reinforcement to prevent buckling of the diagonal reinforcing bars. When evaluating the shear strength of steel fiber-reinforced coupling beams with regard to the ACI provision, the shear strength was predicted more accurately when the shear contribution of the concrete was considered and the diagonal reinforcement was properly confined. [ABSTRACT FROM AUTHOR]

Evaluation of the ultimate strength for the UHPFRC (ultra-high-performance fiber-reinforced concrete) flexural members was conducted. In this study, an experimental program about UHPFRC beams was conducted with the effect of fiber volume fraction, shear span to depth ratio, and compressive strength of matrix as the main variables. Among them, it was found that fiber volume fraction was the variable that had the greatest influence on the ultimate strength. The inclusion of 2% volume fraction steel fiber increases the shear and flexural strength of UHPFRC beams significantly. In particular, steel fiber inclusion changed the mode of failure of beams from diagonal shear failure into flexural failure. For the classification of failure patterns, the ultimate flexural strength and shear strength of UHPFRC members were evaluated using the current design code and UHPC guidelines. Flexural ultimate strength was affected by the size and shape of the stress block and consideration of the matrix's tensile strength. For the accurate shear strength prediction of UHPFRC beams, the tensile strength of the high strength matrix and the effect of steel fiber should be considered. [ABSTRACT FROM AUTHOR]

In this research, flexural performance was evaluated using macro-synthetic fiber-reinforced concrete (MFRC) in structural deck plates. Material tests were performed to evaluate the mechanical properties of the MFRC, and the flexural strength evaluation was conducted in two experiments, positive and negative moment tests. In the material test results, compressive strength and modulus of elasticity of the MFRC were increased compared with normal concrete. Flexural tensile tests showed that, after achieving maximum strength, the deck plates had sufficient residual strength until fracture. Structural tests showed that flexural strength and cracking load of all specimens increased according to macro synthetic fiber dosage. According to the experimental results, we proposed a flexural strength model of a steel deck plate containing macro synthetic fiber. The model showed greater accuracy than the current standard compared with the experimental results. In addition, since it was confirmed that the MFRC steel decks had greater flexural stiffness until yielding, it will be necessary to quantitatively evaluate the effect of MFRC on the effective flexural stiffness of steel decking in future studies. [ABSTRACT FROM AUTHOR]

This study was conducted to evaluate the applicability of concrete-filled steel tube (CFT) columns made from high-performance construction materials. KBC2016, South Korea’s current building code, limits the maximum compressive strength of concrete at 70 MPa and the maximum yield strength of steel at 650 MPa. Similar restrictions to material properties are imposed on major composite structural design parameters in other countries worldwide. With the recent acceleration of the pace of development in the field of material technology, the compressive strength of commercial concrete has been greatly improved and the problem of low tensile strength, known to be the major limitation of concrete, is being successfully addressed by adding fiber reinforcement to concrete. Therefore, the focus of this study was to experimentally determine the strength and ductility enhancement effects, which depend on material composition. To this end, we performed concentric axial loading tests on CFT stub columns made from steel with a yield strength of 800 MPa and steel fiber-reinforced high-strength concrete. By measuring the strain at the yield point of CFT steel during the test, we could determine whether steel yields earlier than ultimate failure load of the member, which is a key design concept of composite structures. The analysis results revealed that the yield point of steel preceded that of concrete on the stress-strain curve by the concurrent action of the strain increase at the maximum strength, attributable to the high compressive strength and steel fiber reinforcement, and the strain increase induced by the confining stress of the steel tube. Additionally, we performed parametric study using ABAQUS to establish the broad applications of CFT using high-performance materials, with the width-to-thickness ratio as the main parameter. Parametric study was undertaken as experimental investigation was not feasible, and we reviewed the criteria for limiting the width-to-thickness ratio as specified in the current building code. [ABSTRACT FROM AUTHOR]

Ultra-high-strength (UHS) fibre-reinforced concrete (FRC) has a much larger tensile strength than normal concrete and engineers should thus consider the tensile strength as a design parameter. However, in the current design codes, the tensile strength of concrete is not considered a major design parameter. It is therefore difficult to design UHS FRC structures using the current design codes. In this study, the indirect tensile strength of UHS FRC was investigated by tests and statistical evaluations. The tensile strength of UHS FRC was found to have a correlation with compressive strength and the content of fibre reinforcement. The indirect tensile strength, splitting strength and flexural strength were influenced by the compressive strength of concrete in an exponential form and also increased with increasing fibre contents. Using this observation and test data from the literature, the effects of compressive strength and fibre content on the indirect tensile strength increase ratio was investigated. Using regression analysis, prediction equations for calculating the indirect tensile strength of UHS FRC were developed, considering the concrete compressive strength and fibre content simultaneously. [ABSTRACT FROM AUTHOR]

In this paper, the effectiveness of steel fiber inclusion on the structural performance of steel fiber reinforced high strength concrete columns was investigated with test of 7-high strength concrete specimens with and without steel fiber. All test specimens were subjected to axial load and reversed cyclic lateral loads. It was shown that test steel fiber inclusion significantly increase the structural performance. Steel fiber inclusion was remarkably effective than the transverse reinforcement about structural performance such as strength and energy dissipation capacity. Steel fiber reinforcement was more effective with high volumetric ratio of transverse reinforcement. Compressive strength of matrix affect to the strength and ductility. High strength matrix column specimens showed better performance than normal strength matrix column specimens. In order to verify the safety of existing strength estimation equations, test results were compared with estimated values. Most of the estimation equations were over estimated the shear strength of concrete. Therefore, in this study, for the safe design of steel fiber reinforced high strength concrete columns, newly developed estimation equation was suggested. [ABSTRACT FROM AUTHOR]