Effect of loading rate on the bond behavior of plain round bars in concrete under lateral pressure

The bond behavior of steel bars in concrete subjected to complex lateral stresses has received wide attention over the last two decades and various bond strength models and bond stress-slip relationships have been proposed. However, the knowledge of how the loading rate affects the bond behavior of steel bars remains limited. In this paper, a total of 237 pull-out specimens were tested to investigate the effect of the loading rate on the bond behavior between plain round bars and concrete under different lateral pressures. The experimental results showed that, when a lateral pressure is applied, the bond performance is greatly affected by the loading rate. For a given lateral pressure, the ultimate and residual bond strengths increase but the slip at the peak bond stress decreases with the increase of the loading rate. The larger the lateral pressure is, the more pronounced the loading rate effect is. Finally, an empirical bond stress-slip relationship considering lateral pressure, the loading rate, the strength of concrete, and the bar diameter is proposed and verified with experimental results.