Bond behavior between steel reinforcing bars and concrete under dynamic loads

In this study, 120 pullout specimens with anchorage length of 5d and 3d (where d denotes the diameter of the rebar) have been tested to investigate the bond performance under dynamic loading. The specimens were divided into 8 groups, with 5 loading rates applied to each group. Besides the loading rate, concrete strength, rebar diameter, and bond length were taken into account. In general, the experimental results indicated that most of the specimens demonstrated a splitting failure pattern, for which abrupt drops in measured load were usually observed following the peak of load-displacement curves. In addition, the bond-slips during the load drop were almost equal to the distance of the ribs of the reinforcing bars. Following the drop, the bond stress increase or decrease periodically with slip induced by the ribs on steel reinforcing bars. Both the bond strength and the bond stiffness showed noticeable increases following the increase of loading rate. An empirical model was developed to describe the bond strength with respect to concrete strength and loading rate. Eventually, the predicted results agree well with the experimental data.