International Concrete Abstracts Portal

Tests were made on 92 knee-type steel fiber reinforced concrete (SFRC) beam-column connections to determine the effect of steel fibers on strength and behavior. Both beam and column had overall sections of 4 x 4 in. (101.6 x 101.6 mm) and length of 16 in. (406.4 mm) each. The column had main reinforcement comprised of two bars of «-in. (12.0 mm) diameter deformed steel bars having yield strength of 67.5 ksi (4745 kgf/cmý) near the outside face and two bars of ¬-in. (6.0-mm) diameter of deformed steel near the inside face of the column. The column had 3/16-in. (5.0-mm) diameter ties of plain mild steel at 3 in. (76.5 mm) center to center. The two bars of 1/2-in. (12.0-mm) diameter near the outside face of the column were continued into the top of the beam to provide main steel. The variables were M/P ratio (moment to axial load) type percentage and aspect ratio (length to diameter) of the fibers. Brass-coated high-strength steel plain fibers of size 1.0 x .01 in. (25.4 x 0.254 mm), « x 0.006 in. (12.7 x 0.152 mm), 1.0 x 0.016 in. (25.4 x 0.406 mm), and mild steel fibers of 0.011-in. (0.282-mm) diameter having aspect ratio of 10, 25, 50, 75, and 100 were used. The percentage of fibers (by volume of concrete) varied from 0.5 to 2.0. Connections having conventional reinforcement only were also tested. The test results indicated that steel fiber reinforced concrete is very effective in increasing ductility and crack resistance in the connection region. Ultimate rotation of SFRC connections was six to nine times that of conventional connections. There was an increase in moment capacity of 15 to 30 percent with increase in fibers from 0.5 to 2.0 percent by volume. Moment capacity increased by about 50 percent when the aspect ratio of the fibers was increased from 10 to 100.

Fibro-ferrocrete can be visualized as a new material that judiciously combines reinforced concrete, ferrocement, and fiber reinforced concrete to give a strong and effective structural material. This material can be fabricated readily into beams and flat plate elements that are structurally efficient and strong. Tests of six fibro-ferrocrete one-way slabs subjected to flexural loadings are reported. The factors affecting the strength of such slabs are examined. A theory is presented to determine the flexural strength of fibro-ferrocrete one-way slabs. The ultimate strengths obtained from five of the six tests exceed the calculated values derived from the proposed theory, usually by 20 to 30 percent.

Paper reviews seven test specimen geometries that have been used to determine the shear performance of fiber reinforced concrete (FRC) materials. All the geometries are modified standard quality control test specimens--modified cubes, beams, or cylinders. The performance of FRC materials can be characterized by two fracture parameters--fracture toughness, which gives the resistance to cracking, and toughness index, which quantifies the post-first-crack toughness. The shear strength results are similar for the various test geometries used in the study. The shear strength of steel FRC mixes is shown to be independent of fiber content, whereas the shear strength of polypropylene FRC decreases with increasing fiber content and the shear strength of glass FRC increases with increasing fiber content. The post-cracking toughness increases uniformly with increasing fiber content over the range of fiber contents studied. This increase in toughness is observed for all three fibers--steel, polypropylene, and glass fiber.

The composite material concept is commonly used to predict the tensile strength of fiber reinforced concrete. Application of this concept implies that the fiber pullout resistance is mobilized to a large extent when the peak tensile strength is reached. The validity of this assumption is checked in this paper using the available results of pullout tests on steel fibers and direct tension tests on steel fiber reinforced concrete. The measured values of fiber pullout stiffness and fiber reinforced concrete strain at peak stress are used to derive conclusions regarding the contribution of the pullout mechanism of fibers to the tensile strength of fiber reinforced concrete.

Theoretical analysis is used to predict bending properties of strain-softening materials from known stress-strain relationships in uniaxial tension and compression. Conversely, given the bending load-displacement relation, it is possible to predict the entire tensile strain-softening response. Bending properties of a polymer concrete have been obtained using the proposed theory and given stress-strain relationships. It is shown that the bending strength is higher than the tensile strength due to the strain-softening effect.