Behavior of Steel Fiber Reinforced Concrete Knee-Type Beam-Column Connections


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Title: Behavior of Steel Fiber Reinforced Concrete Knee-Type Beam-Column Connections

Author(s): Roop L. Jindal and Ved Raj Sharma

Publication: Special Publication

Volume: 105


Appears on pages(s): 475-492

Keywords: beams (supports); columns (supports); connections; ductility; cracking (fracturing); fiber reinforced concretes; metal fibers; moments; Structural Research

Date: 12/1/1987

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.