In this study, a bond-slip model is proposed to take into account the effects of corrosion on the bond characteristics between extremely low-strength concrete and plain reinforcing bars. The proposed bond-slip model is based on reversed cyclic lateral loading tests of nearly full-scale reinforced concrete columns with reinforcing bars corroded to different levels. The columns taken into consideration during the current study were part of an extensive experimental program designed to study the performance of older columns at Istanbul Technical University. The columns were representative of a large number of underperforming reinforced concrete buildings prone to seismic actions throughout the world. Test results demonstrated that the corrosion of reinforcing bars had a significant effect on the strength and deformability characteristics of substandard reinforced concrete columns subjected to the combined actions of axial and reversed cyclic lateral loads. Taking this aspect into consideration, a novel bond-slip model is established to estimate the variation in bond strength degradation and the bond strength as a function of the level of corrosion of the reinforcing bars. Furthermore, the predictions of the proposed model are also verified with experimental results from the literature. (C) 2015 American Society of Civil Engineers.