Investigation on the dynamic bond-slip behaviour between steel bar and concrete

Abstract

The bond behaviour between steel bar and concrete affects the response of reinforced concrete (RC) structures subjected to static and dynamic loads. Many studies have investigated the influencing factors on static bond behaviour between steel bar and concrete, e.g., cover depth to rebar diameter ratio (c/d) and concrete strength and various empirical formulae have been proposed to quantify the static bond strength, but the study of dynamic bond strength is very limited. As a result, in the analysis of dynamic structural responses, either perfect bond is assumed or static bond strength is adopted, which may lead to inaccurate structural response predictions. In this study, dynamic bond-slip behaviour between steel bar and concrete is numerically investigated by using the finite element (FE) model developed in LS-DYNA and verified against testing results. The effects of the concrete specimen shape, c/d ratio and concrete strength on the dynamic pull-out test are examined. It is found that the splitting of concrete dominates the failure mode of dynamic bond-slip behaviour. The ultimate bonding load is enhanced with the increase of loading rate. It is observed that the increase of bond strength relates to the dynamic increase factor (DIF) of concrete strength. The parametric studies show that among all considered factors, the shape of the pull-out test specimens has a minor effect on the ultimate bonding load, which on the other hand is highly dependent on the concrete strength and c/d ratio owing to the strain rate effect. An empirical relation of DIF of bond strength as a function of c/d ratio, concrete strength and strain rate is proposed based on the numerical results. A case study of drop weight test on an RC beam is then carried out to demonstrate the influence of considering the dynamic bond strength in numerical prediction of structural responses under dynamic loading.