Proposal for Bond Strength Considering Bond Characteristics of Beam Flexural Rebar on Interior Beam-Column Joints. Part II: Focusing on Column Axial Load, Beam Flexural Rebar Yield Strength and Diameter

Abstract To ensure the stability of interior beam-column joints under seismic loads, various influencing factors are incorporated into current design criteria in different countries. However, the design concepts and the influencing factors reflected in each country are different. The bond characteristics of beam longitudinal rebar penetrated the joint are mainly influenced by the compressive strength of concrete and are presented in the form of average bond stress. In Part I, the effect of concrete compressive strength on the bond characteristics of beam longitudinal rebar was directly investigated through a bond test that directly simulated the stress state of the joint. In this study, factors affecting the bond strength and required column depth were proposed by considering the bond characteristics based on the column axial force ratio and the yield strength of the beam longitudinal rebar. The experiment involved producing 14 test specimens and performing cyclic loading, taking each variable into consideration. Based on the experimental results, the proposed equation for the effect of column axial force ratio on the bond strength showed an excellent prediction performance compared to the current design equation with a coefficient of variation of 30.7%. In addition, a bond stress equation that reflects the stress difference of the beam longitudinal rebar was proposed using the strain values measured at both ends of the joint.