Title:
Bond Strength Improvement of Reinforcing Bars with Specially Designed Rib Geometries
Author(s):
Bilal S. Hamad
Publication:
Structural Journal
Volume:
92
Issue:
1
Appears on pages(s):
3-13
Keywords:
bond (concrete to reinforcement); deformed reinforcement; pullout tests; bonding; reinforced concrete; reinforcing steels; Structural Research
DOI:
10.14359/1464
Date:
1/1/1995
Abstract:
The objective of the research program was to evaluate the effect of rib geometry on bond-slip characteristics of deformed bars in reinforced concrete structures. In one phase of the study, 56 specially machined bars were tested in rectangular eccentric pullout specimens. The bars were hot-rolled carbon-steel Grade 60 plain round bars with a diameter of 0.811 in. (20.6 mm) and were machined to simulate No. 6 American bars with parallel or bamboo deformation pattern and with different deformation properties. The variables were the bar rib face angle, rib spacing, rib height, and concrete strength. Failure of the pullout specimens was governed by splitting of the concrete cover over the anchored bar. In the second phase of the study, 13 beams were tested in positive bending with two splices of 0.811-in. (20.6-mm) Grade 60 bars in a constant moment region at the center of the span. The splice length was selected so that the bars would fail in bond, splitting the concrete cover in the splice region. The bars were machined along the splice length to different deformation patterns identical to those investigated in the first phase. No transverse reinforcement was provided in the splice region. Variables in the beam splice tests included the bar rib face angle, rib spacing, and rib height. Test results indicated that the bond strength and bond-slip resistance of the specially machined bars varied with the bar rib face angle, rib spacing, and rib height. The trends of the results were independent of concrete strength. Using the results, design recommendations were made concerning optimum rib geometries of deformed bars with superior bond-slip characteristics.