Bond Strength of Lap-Spliced Bars

Abstract

The performance of reinforced concrete structures depends on adequate bond strength between concrete and reinforcing steel. This article reports on a study of the bond strength of lap-spliced bars. The authors note that calculation methods to evaluate the strength of tension lap splices are based primarily on nonlinear regression analysis of test results. However, the results from these analyses may not be generalizable to situations beyond the domain of the data. In this study, the authors developed an expression for the calculation of bond strength based on a physical model of tension cracking of concrete in the lap-spliced region. Two different types of failure modes are considered: horizontal splitting that develops at the level of the bars (side-splitting failure), and vertical splitting that develops along the bar on the face cover (face-splitting failure). The developed expression was verified using results from 203 unconfined and 278 confined beam tests where the splice region was subjected to constant moment. Results showed that the relation between splice strength and splice length is not linear. The use of the fourth root of the concrete strength provides an improved estimate regarding the behavior of lapped splices as compared with the square root. In addition, the effect of the thickness of the concrete cover surrounding the bar is not linear.