International Concrete Abstracts Portal

Tests were made on 44 beams to study the effect of steel fibers as shear reinforcement and to determine if there was any increase in the shear/moment capacity and change in the mode of failure. Span length of 30 in. (762 mm) was used for shear-span ratios (a/d) of 2.0 and 2.4, and 60 in. (1524 mm) for a/d ratios of 3.6 and 4.8. Steel fibers of 1% by volume were used in all SFRC beams. The variables were type of fibers, aspect ratio (l/d) of the fibers and the shear span ratios. Test results showed that shear and moment capacities of SFRC beams varied from 1.50 to 1.92 and 1.12 to 1.39 times, that of conventional reinforced concrete beam, respectively. Pbde of failure changed from shear mode to moment mode when SFRC was used. Steel fibers having aspect ratio of 75 or thin fibers were found to be most effective for increasing the shear capacity of SFRC beams. A design method has been suggested for analysing and designing SFRC beams. Theoretical results based on this method compare favorably with the test results.

From exploratory research of reinforced fibrous concrete, it has been shown that fibrous concrete is potentially superior and less costly than the conventional reinforced concrete. The testing program consisted of ten beam column joints with half of these joints containing 1.5 percent by volume of concrete of steel hooked end fibers. The beam column joints were constructed with less hoops than a conventional seismic joint would have, ac-cording to design specifications of the American Concrete Institute code ACI 318-77). In studying the behavior of these beam column joints, two failure conditions were found: 1) critical regions whose inelastic behavior is controlled by bending, and 2) critical regions whose inelastic behavior is controlled by high shear existing in the region. The results of the testing will be described. From the analysis of the results, it can safely be concluded that the hooked end steel fibers in the joint region provided: 1) better bond; 2) better confinement of the concrete; 3) a stiffer member; 4) higher moment capacity; 5) higher shear strength; 6) more ductility; and 7) significant improvement in the energy dissipation capacity than did the plain concrete joint.

This paper presents an overall evaluation of the observed behavior of fiber reinforced concrete under dynamic loading. The term dynamic loading is used to describe either high strain rate monotonic loading (impact) or cyclic loading under high stress range, high strain rates (simulating earthquake loading). Particular emphasis is placed on the evaluation of the fracture energy (or toughness) and fatigue life of this composite. The research program comprises four related parts dealing re-spectively with: 1) the effect of strain rate on the pull-out behavior of fibers in mortar, 2) the surface energy of fiber reinforced mortar prisms in tension, 3) the energy absorbed by fiber reinforced mortar beams subjected to impact loading and 4) the behavior in compression of fiber reinforced concrete cylinders under high strain rates monotonic and cyclic loadings. While Parts 2 and 3 of the program deal with steel fibers only, Parts 1 and 4 involve also glass, polypropylene and polyester fibers.

This paper reports a few results of the experiments carried out in order to investigate the characteristics of deflection of the polymer fiber and the hybrid fiber reinforced concrete beams under bending load. Some results on the dynamic strength test for the polymer and hybrid fiber reinforced concrete beams by a Charpy impact tester modified for concrete specimens are also refered in this paper. The polymer fibers used in polymer fiber reinforced concrete are generally filaments with extremely small diameter. The fibers used in this study are relatively thick with the rectangular cross section of 2 by 0.6 mm. From these experiment, it may be found that the flexural strength of concrete is improved by the addition of the polymer fibers. The polymer fiber reinforced concrete beams showed great endurance after the initiation of cracks in the specimens. A method by a modified Charpy impact tester was proposed in this study for evaluating the resistance of concrete against impact load. According to the results obtained using this method, the resistibility of the polymer and the hybrid fiber reinforced concrete against impact load is about double that for fiber-free concrete.

A method for adapting existing pavement thickness design curves and formulas for "special" concretes is presented. The need for doing this is discussed; i.e., special concretes made, for example, with fiber reinforcement or high-range water reducers have material properties (specifically changed fatigue endurance and the effects of maturity) which are different from the long-assumed properties that "normal concretes" possess and upon which current design curves are based. Without making these adaptions, wasteful over-design or failures from underdesign can occur. An example is given