Effect of Confinement on Bond Strength of Hot-Dip Galvanized Lap Splices in High-Strength Concrete

Abstract

Galvanizing reinforcing steel is one of the methods used to protect steel bars against corrosion. In 2001, a research program was started at the American University of Beirut (AUB), Beirut, Lebanon, to experimentally evaluate the effect of hot-dip galvanizing on the bond capacity of tension lap splices anchored in full-scale beam specimens designed to fail in bond splitting mode. The test results indicated that the use of galvanized bars had a negligible effect on bond strength of reinforcement in normal-strength concrete. Galvanising, however, caused an average of 20% decrease in bond strength of reinforcement in high-strength concrete. The primary objective of the research reported in this paper was to find a solution to eliminate the bond reduction of galvanized bars in high-strength concrete. It was important to evaluate the potential positive effect of the addition of transverse reinforcement in the splice region. One hypothesis to be tested was that such transverse reinforcement would ensure uniform bond stress distribution over the entire splice length, thus mobilizing all bar lugs along the splice in the stress transfer mechanism between the bar and the surrounding concrete, and hence would lead to increasing the bond strength of galvanized bars. The second hypothesis to be checked was whether the aforementioned mechanism of mobilizing all bar lugs along the splice in the stress transfer mechanism would reduce the significant decrease in bond strength of galvanized bars relative to black bars in high-strength concrete. Eighteen, full-scale beam specimens, designed to fail in bond-splitting mode, were tested in positive bending. Each beam was reinforced with bars spliced in a constant moment region at midspan. The main variables were bar size and the amount of transverse reinforcement in the splice region. The test results indicated that, whereas confinement increased the bond strength of galvanized bars and black bars, confinement did not have a significant positive effect on the bond strength of galvanized bars relative to black bars.