# The Influence of Interlock Loss between Rebar and Concrete on Bond Performance of RC Member
## 1 Introduction  
Rebar corrosion is one of the typical causes of deterioration in reinforced concrete structures. It is caused by various factors such as chloride attack and carbonation and can lead to serious degradation of structural performance such as load-bearing capacity or ductility [1, 2, 3, 4]. Therefore, it is necessary to develop a method to evaluate current and future structural performance of reinforce concrete structures with rebar corrosion for infrastructure management. Rebar corrosion causes rebar shape changes, and corrosion products generate expansion stress and cause cracks around rebars. When the corrosion cracks reach concrete surface, deterioration factors can easily ingress and corrosion is accelerated. Finally, rebar corrosion leads to spalling of cover concrete [5, 6]. During this process, bond between the rebar and the concrete deteriorates, and it affects load-bearing mechanisms.  
It is known that bond deterioration impairs the stress transfer between rebar and concrete, causing a decrease in flexural capacity, stiffness, and crack dispersibility [7, 8, 9, 10]. On the other hand, as long as anchorage of the main rebar is kept sound, bond deterioration can improve shear capacity by the formation of a tied arch mechanism [11, 12].  
Bond consists of three main components: mechanical interlock, chemical adhesion, and friction resistance. Among these, mechanical interlock, which is caused by the bearing pressure between lug and concrete, is highly effective [13, 14]. In order to obtain strongmechanical interlock, deformed bars with lugs are generally used. Many researchers have investigated the effects of bond deterioration due to rebar corrosion [15; 16; 17; 18; 19]. These investigations primarily focused on the pull-out behavior of rebar or the response as a RC member with corrosion. However, these discussions cannot evaluate the change in the contribution of the bond constituting components mentioned above and corrosion cracks. A bond deterioration mechanism is complex; interlock condition changes due to section loss, chemical bond and friction resistance are lost, and the cracks around rebar reduce the bearing strength of concrete [7; 20; 21].  
For an accurate understanding of the phenomenon, it is necessary to separate out multiple factors of bond deterioration. Thus, the authors focused on the interlock, which is a dominant factor in bond components, without corrosion cracks in this research. The aim of this study is to evaluate the influence of changing the interlock condition on the load-bearing mechanism and bond performance of RC beams through the experiment and finite element (FE) analysis. After conducting loading tests on the beams with different interlock conditions, they are analyzed by the FE model that reproduces the shape of rebar using solid elements precisely. This FE model applied very fine mesh, in which mortal and coarse aggregate was modeled individually. These models were verified by reproduction analysis of beam tests and pull-out tests of rebar from concrete. Then, the analytical case studies simulating non-uniform or partial shape change in cross sections and in axial direction were conducted.