International Concrete Abstracts Portal

Infrastructural application of steel fiber reinforced concrete to access hole covers is explored. It has been shown that bar reinforced concrete covers further reinforced with fibers are suitable candidates for access hole covers in medium- and heavy-duty applications. The covers possess increased cracking strength due to the crack-arresting mechanism of the fibers. A greater ultimate load also results, thanks to the increase in shear strength afforded by the fibers. Further, these covers also possess good energy absorption capacity and local anti-splitting characteristics due to the presence of fibers everywhere in the mass.

In multistory framed structures, three kinds of connections exist, namely, cross-type, tee-type, and knee-type. Experimental investigations were made to study the behavior of 50 such beam-column connections of conventional and steel fiber concrete (SFC) when tested under static, as well as slow-cycle fatigue, loading. In all, 10 cross-type specimens of full-scale two-span beam with column stub were tested. Four cross-type connections were cast with conventional concrete, two with steel fibrous concrete in the entire length and four with SFC in the joint region only. The test results showed that SFC improved the ductility at the joint region, increased load-carrying capacity, decreased crack width, eliminated shear reinforcement, and overcame the problem of spalling of concrete in the joint region. The testing work also included 20 tee-type and 20 knee-type connections with 12 of each tested under static load and eight under slow-cycle fatigue load. The percentage was kept as 0.0, 0.6, 0.8, and 1.0 of concrete volume. Instrumentation was done to measure deflections, rotations, strains, and crack widths.

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.

Use of reinforced fiber concrete in buildings, for construction of an adequate section to resist a flexural failure, has been under investigation by engineers in the past decade. Design and analysis methodologies are discussed in the paper so this type of construction can be developed successfully by engineers. In the first part of the paper, results from 13 beams that were tested at New Jersey Institute of Technology are presented to show the nature of the flexural behavior. These beams are for: 1) normal concrete, 2) high-strength concrete, and 3) lightweight concrete with and without fibers. Most of the results from these tests have not been reported previously. A computer program will also be shown that accurately predicts the flexural behavior of these beams and other reinforced fiber concrete members. Using these test results and the computer program, inelastic and elastic behavior in flexure are discussed. The majority of the paper deals with analysis and design methods. All past methods of analysis are discussed briefly. A method that has been developed by NJIT is explained for analyzing regular singly reinforced, doubly reinforced, and T-beams. The {rho}b criteria is explained for each case, and analysis equations and design methodology are shown for each type of beam. Hence, the paper shows the state-of-the-art in analysis with the examples, and presents a rational design scheme for use by the design engineer that will help in the adoption of such a construction material.