The bond deterioration of plain round bars subjected to lateral tensile-compressive stresses

Plain round bars have been widely used as reinforcement in historical concrete structures. One important aspect of the assessment of these old buildings is to verify whether the anchorage between concrete and plain round bars is reliable or not. Thus the bond behavior of the plain round bar is widely studied in recent years. Many investigations showed that the lateral stress state of the bar has great influence on its bond behavior. When seismic loads are considered, the steel bars located at corners or beam-slab joints may be simultaneously subjected to tensile and compressive stresses which affect the anchorage between the bars and concrete. So far, a few studies on the bond behavior of the plain round bar considering the lateral tensile compressive stresses have been reported, however, the mechanism of bond deterioration has been seldom revealed in theoretical manner. In this paper, an analytical approach to the bond deterioration of plain round bars under lateral tensile-compressive stresses is presented. Based on the theory of elasticity, the contact condition of the bar/concrete interface is discussed, and an analytical solution for the ultimate bond strength is further derived when the interface keeps closely contact. A total of 174 pull-out specimens are adopted to verify the analytical solution. The results show that, with the shrinkage of concrete, the geometric and mechanical parameters of bars and concrete known, it is proper to determine the contact situation of the bar/concrete interface and predict the bond strength of plain round bars under lateral tensile-compressive stresses.