Bond of substandard laps in RC beams retrofitted with post-tensioned metal straps

This article investigates the bond splitting performance of lapped steel bars in tension. Twelve RC beams with substandard laps (lap length=25 bar diameters) at midspan were tested in flexure. The variables examined include the bar diameter, concrete cover and three different confinement conditions at midspan, i.e. no confinement, internal steel stirrups and external Post-Tensioned Metal Straps (PTMS). The test results show that, in comparison to unconfined specimens, PTMS confinement enhances the bond strength of the lapped bars by up to 120%. Based on the results of this study, an innovative equation is proposed and validated to calculate the additional bond strength provided by PTMS confinement. The equation can be used for assessment and retrofit of substandard lapped bars in RC structures and should prove useful in practical retrofitting applications.