This paper presents the results from an experimental program and an analytical assessment of the influence of addition of fibers on mechanical properties of concrete. Models derived based on the regression analysis of 60 test data for various mechanical properties of steel fiber-reinforced concrete have been presented. The various strength properties studied are cube and cylinder compres- sive strength, split tensile strength, modulus of rupture and postcracking performance, modulus of elasticity, Poisson's ratio, and strain corresponding to peak compressive stress. The variables considered are grade of concrete, namely, normal strength 35 MPa, moderately high strength 65 MPa, and high-strength concrete 85 MPa, and the volume fraction of the fiber Vf=0.0, 0.5, 1.0, and 1.5%. The strength of steel fiber-reinforced concrete predicted using the proposed models have been compared with the test data from the present study and with various other test data reported in the literature. The proposed model predicted the test data quite accurately. The study indicates that the fiber matrix interaction contributes significantly to enhancement of mechanical properties caused by the introduction of fibers, which is at variance with both existing models and formulations based on the law of mixtures. 85 MPa with various fiber dosages Vf=0, 0.5, 1.0, and 1.5%. An empirical relationship for various mechanical properties of SFRC has been proposed. The proposed model attempts to bring out the significance of fiber matrix interaction in all the strength properties. This study reports the experimental results of the strength properties of SFRC, namely, cube and cylinder compressive strength, split tensile strength, modulus of rupture, modulus of elasticity, Poisson's ratio, and strain corresponding to peak com- pressive stress. Empirical relationships were developed for vari- ous strength properties based on the regression analysis of the 60 test data. It is expected that these proposed models would be helpful in assessing the strength properties of fiber-reinforced concrete based on the matrix strength and fiber-RI.

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Mechanical Properties of Steel Fiber-Reinforced Concrete

ACI Structural Journal/July-August 2002 ACI Structural Journal, V. 99, No. 4, July-August 2002. MS No. 01-402 received November 27, 2001, and reviewed under Institute publication policies. Copyright © 2002, American Concrete Institute. All rights reserved, including the making of copies unless permission is obtained from the copyright proprietors. Pertinent discussion will be published in the May-June 2003 ACI Structural Journal if received by January 1, 2003. ACI STRUCTURAL JOURNAL TECHNICAL PAPER

Shear Strength of Steel Fiber-Reinforced Concrete Beamswithout Stirrups

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Structural behavior of ultra high performance concrete beams subjected to bending

Experimental and numerical study on mechanical properties of Ultra High Performance Concrete (UHPC)

This paper presents the results of experimental tests carried out on rectangular simply supported beams made of hooked steel fibre reinforced concrete with and without stirrups, subjected to two-point symmetrically placed vertical loads. The tests, carried out with controlled displacements, allow one to record complete load–deflection curves by means of which it is possible to deduce information on dissipative capacity and ductile behaviour up to failure. Depending on the amount of transverse reinforcement, volume fraction of fibres added in the mix and shear span, the collapse mechanism is due to predominant shear or flexure, thus showing the influence of the aforementioned structural parameters on the load carrying capacity and the post-peak behaviour of the beam. In particular, the results show that the inclusion of fibres in adequate percentage can change the brittle mode of failure characterizing shear collapse into a ductile flexural mechanism, confirming the possibility of achieving analogous performance by using reinforcing fibres instead of increasing the amount of transverse reinforcement. The ultimate values of the shear stresses recorded experimentally are compared with the corresponding values deduced by semiempirical expressions available in the literature and the correlation is satisfactory.

Effectiveness of stirrups and steel fibres as shear reinforcement

Shear Behavior of High-Strength Fiber Reinforced Concrete Beams

Eight high-strength concrete beams with different fiber contents and shear span-depth ratios were tested to study the influence of fiber addition on ultimate load, crack propagation, flexural rigidity, and ductility. The addition of steel fibers enhanced the strength and increased the ductility and flexural stiffness of the tested beams. A semi-empirical equation is proposed to estimate the effective moment of inertia of simply supported high-strength fiber reinforced concrete beams. The estimated deflections using this equation agree well with the experimental values. At ultimate conditions, the length of the plastic hinge developed was found to be proportional to the fiber content.

Flexural behavior of high-strength fiber reinforced concrete beams

Effect of the concrete compressive strength and tensile reinforcement ratio on the flexural behavior of fibrous concrete beams

Fourteen prestressed high-strength concrete beams were tested to study their torsional behavior. The major variables were the concrete compressive strength, the aspect ratio of the beam cross section, the prestressing level, and the amount of torsional reinforcement. Keeping the area constant, three different cross-sectional dimensions, 240 × 240 mm, 170 × 340 mm, and 140 × 420 mm, were used to give aspect ratios of 1, 2, and 3, respectively. The concrete compressive strengths were 70 and 90 MPa (10,000 and 13,000 psi), and the beams were subjected to two levels of prestressing, corresponding to 0.05 f ′c and 0.10 f ′c. Test results showed that the torque-twist relations for the tested beams were approximately linear up to cracking, and thereafter they were nonlinear. The aspect ratio and the concrete compressive strength influence both the torsional strength and the torsional stiffnesses at all stages of loading. Several theoretical methods available in the literature and developed for normal-strength co...

Prestressed High-Strength Concrete Beams Under Torsion

The paper presents an experimental and theoretical study on immediate and long-term deflections of high-strength concrete beams. Twelve beams with 85 MPa (12,300 psi) compressive strength and having tension and compression rebars and steel fibers were tested. The experimental results show that the addition of fibers increases the flexural rigidity of the beams, thus reducing the immediate and total long-term deflections under sustained service load. The beneficial effect of the compression reinforcement in controlling the long-term deflection is observed in beams without fibers. However, for beams having steel fibers and compression reinforcement, the behavior depends on the amount of the two types of reinforcement, and their excessive amount may have an inauspicious effect on the long-term deflection. A method is presented for computing the effective moment of inertia of fibrous concrete beams, and a modification is suggested to the long-term multiplier of the ACI Code to include the effect of fibers and high-strength concrete.

Faisal F. Wafa

Papers

Shear Behavior of High-Strength Fiber Reinforced Concrete Beams

Flexural behavior of high-strength fiber reinforced concrete beams

Effect of the concrete compressive strength and tensile reinforcement ratio on the flexural behavior of fibrous concrete beams

Prestressed High-Strength Concrete Beams Under Torsion

Influence of steel fibers and compression reinforcement on deflection of high-strength concrete beams