Abstract
Composite behavior of reinforced concrete requires adequate bond between concrete and
steel reinforcement that can transfer stresses between them. The bond strength is influenced
by cover to the reinforcement and development length. Experimental investigation was carried
out and twisted steel bars conforming to BS 4461 were used in high strength concrete to study
bond strength characteristics. The post peak bond behavior was studied by using displacement
controlled universal testing machine. The results of this experimentation confirmed that by
increasing the cover/bar diameter ratio, bond strength increased and slip decreased for both
small and large diameter twisted steel bars. This increased confinement reduced the uneven
bond stress distribution along the development length. Stress concentration on the front key
(concrete between two ribs) was reduced due to its continuity along the twisted steel bar.
Hence it offered maximum possible resistance to bond failure and the bond strength
increased. Similarly by increasing the development length, bond strength and corresponding
slip both increased. Another fact visible from all figures and observed in all samples, is that as
the first concrete key failed there was a sudden drop in bond strength due to the formation of
longitudinal splitting cracks. These cracks are visible from the surface of the cylinder. Once a
key is failed, failure propagated immediately.
K. Ahmed, Z. A. Siddiqi, M. Ashraf , A. Ghaffar. (2008) Effect of Rebar Cover and Development Length on Bond and Slip in High Strength Concrete , Pakistan Journal of Engineering and Applied Sciences, Volume 2, Issue 1.
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