Efficient modeling of steel bar slippage effect in reinforced concrete structures using a newly implemented nonlinear element

In structural modeling of reinforced concrete (RC) structures, a common assumption lies in perfect bonding between steel reinforcing bars and the surrounding concrete. This paper aims to assess this assumption and investigate the need and importance of considering imperfect bonding (i.e., steel bar slippage or bond-slip) for predicting the nonlinear behavior of RC columns. To this end, an efficient finite element model capable of capturing bond-slip is required to evaluate the effect of imperfect bonding. Thus, this study first developed a geometrically nonlinear fiber-based frame element considering steel bar slippage and implemented this element in OpenSees with hybrid corotational transformation. Subsequently, using the newly developed element, the effect of imperfect bonding on the behavior of RC columns was investigated. In this regard, the role of bond-slip was studied under different scenarios, including hooked or unhooked ends of longitudinal steel bars in the anchorage area, low or high load levels, and short- or long-duration earthquake ground motions. The results reaffirm the need for prudent consideration of imperfect bonding for advanced finite element modeling of RC structures in several scenarios.