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Reports on an investigation on the behavior of high-strength concrete beams (with concrete compression strength equal to 11,600 psi or 80 MPa), with and without steel fiber reinforcement, to determine their diagonal cracking strength as well as nominal shear strength. Experimental data on the shear strength of steel fiber reinforced high-strength concrete beams are currently scarce to nonexistent. Twenty-two beam specimens were tested under monotonically increasing loads applied at midspan. The major test parameters included the volumetric ratio of steel fibers, the shear span-to-depth ratio, the amount of longitudinal reinforcement, and the amount of shear reinforcement. It was found that steel fiber reinforced high-strength concrete beams effectively resist abrupt shear failure. Such beams exhibit higher cracking loads and energy-absorption capabilities than comparable high-strength concrete beams without fibers. Empirical prediction equations are suggested for evaluating the diagonal cracking strength as well as nominal shear strength of steel fiber reinforced high-strength concrete beams.

It is well recognized that fiber reinforced concrete (FRC) exhibits a number of superior properties relative to plain concrete, such as improved strength, ductility, impact resistance, and failure toughness. These advantageous features of FRC can lead to novel structural applications, for which standard design and analysis procedures must be supplemented by numerical modeling (for example, the finite element method). This, in turn, makes necessary the development of satisfactory constitutive models that can predict the behavior of FRC under different load conditions, both monotonic and cyclic. In this paper, a constitutive model for FRC is developed loosely within the theory of mixtures. For plain concrete, an anisotropic, strain-based, continuum damage/plasticity model with kinematic and isotropic damage surfaces is developed. To represent the effect of the fibers, a simplified model that accounts for the tensile resistance of the fibers and the enhanced tensile resistance of the plain concrete is proposed. The predictions of the FRC constitutive model are compared to data from laboratory tests of steel fiber reinforced concrete (SFRC) specimens under uniaxial and biaxial loadings.

Partially prestressed beams contain both prestressed and non-prestressed reinforcement. Addition of steel fibers results in an increase in first crack moment and flexural strength and a decrease in deflection and reinforcement stresses. This paper presents an analytical method to compute the deformation of partially prestressed beams made with fiber reinforced concrete. A computer program was developed to evaluate the theoretical moment-curvature and moment-deflection relationships. It uses the linear and nonlinear stress-strain relationships of the composite materials. Strain compatibility concept is incorporated to obtain the stresses in concrete, prestressed steel, and non-prestressed steel. The cracking moment and the nominal flexural strength are also computed. The method can analyze prestressed sections of rectangular, T, I, and box shapes. The analytical predictions of the proposed method agree well with experimental results.

It is well recognized that steel fiber reinforced concrete composites exhibit improved resistance to fracture and impact loads. Both fracture and impact resistance are primarily governed by the toughness characteristics of the material defined by its energy-absorption capacity. Toughness can be measured by carrying out tests involving direct tension, compression, or flexure. However, flexural tests are favored for measurement of toughness because of their simplicity and also their close representation of the stress conditions under field conditions. The test procedures for the measurement of toughness indexes given in codes of practice such as ASTM C 1018, JCI-SF4, JSCE-SF4, and ACI 544 help to obtain information on the qualitative performance of different materials and mix designs. Little information has been reported on the toughness characteristics of slurry-infiltrated fibrous concrete (SIFCON), which is basically a material formed by infiltrating a preplaced "fiber stack" with a cement slurry. This paper describes the details of toughness tests carried out on SIFCON at the Structural Engineering Research Centre, Madras, India, and summarizes the results of the investigations.

Experiments were performed on concrete specimens reinforced randomly with polypropylene fibers. To obtain the true properties of the fibers, their tensile stress-strain diagram was obtained through tests. The fibers used had a tensile strength of 2800 kgf/cm 2 (40,000 psi), a failure strain of about 11 percent, and a modulus of elasticity of 2.55 X 10 5 kgf/cm 2 (3,642,857 psi). Then, the 7- and 28-day polypropylene fiber reinforced concrete (PFRC) samples with 0, 0.5, 1.0, 1.5, 2.0, and 2.5 percent by volume of fibers were tested in splitting tensile and compressive strength tests, and the tensile strength, maximum tensile strain, and compressive strength versus percentage by volume of fibers diagrams were plotted. The results show that compressive strength did not change significantly, but tensile strength had an increase of about 80 percent. Significant improvement in ductility was also achieved. The tests also showed that the best improvement was obtained at an optimum percentage by volume of fibers of about 1.5 percent.