Bond performance of ribbed bars in concrete: effects of loading rate and lateral tension

Abstract

This paper presents an experimental study on the effects of lateral tension and loading rate on the local bond performance of ribbed bars in concrete. The results show that, up to a loading rate of 10 mm/s, the mode of bond failure is independent of the loading rate but is closely related to the cover depth, concrete grade and level of lateral tension. It is also shown that the bond strength of ribbed bars increases with the increase of loading rate but decreases with an increase in lateral tension. The increase or decrease ratio becomes larger when splitting failure occurs. Specifically, for pull-out and splitting failure, the bond strength decreases by 8% and 22% when the lateral tension increases from 0.0 to 0.6 times the tensile strength of concrete but increases by 22% and 28% when the loading rate increases from 0.01 to 10 mm/s, respectively. The slip at peak bond stress is rate-insensitive. It can be taken as 0.18 times the rib spacing for pull-out failure but decreases linearly with the increase of lateral tension for splitting failure. Finally, a bond stress–slip model with three parameters is suggested for different levels of lateral tension and loading rates.