An analysis of the ultimate strength of lapped joints of compression reinforcement

Abstract

Synopsis Bond failure of ribbed reinforcing bars generally takes place by splitting of the surrounding concrete cover, unless heavy confining reinforcement is present. The bond action of the bars must therefore exert a radial bursting force on the concrete cover, and so the ultimate strength of a lapped joint may be calculated by equating the bursting force produced by bond to the ultimate confining force on the lapped bars provided by the member. In this paper, expressions are derived for the relationship between the stress developed in a lapped bar and the resultant bursting force and they show that this depends mainly upon the strength of the concrete in the member and the deformation characteristics of the bar. The contribution made by bearing of the ends of lapped bars to the ultimate strength of compression laps is also evaluated. Values of lap strength calculated from the analysis are shown to be in good agreement with results obtained from tests on lapped joints in reinforced concrete columns.