THE EFFECTS OF THE DE-BONDING OF BEAM LONGITUDINAL REBARS ON THE STRUCTURAL BEHAVIOR OF BUCKLING RESTRAINED BRACED RC FRAMES WITH A GUARANTEED HINGE POSITION

The de-bonding of longitudinal rebars is a method of suppressing the damage range of reinforced concrete (RC) structures. According to previous studies, in RC beam members, the damage can be concentrated on the hinge position by de-bonding the longitudinal rebars. However, the restoring force characteristic becomes a slip type, and energy dissipation becomes poor. Therefore, in this study, to secure energy dissipation while suppressing the damage range, a structural system was adopted in which the buckling restraint brace (BRB) was attached to the RC frame with de-bonding of the beam longitudinal rebars. Structural tests and finite element analysis were conducted. The purpose was to grasp the effects of the de-bonding of beam longitudinal rebars on the structural behavior of buckling restrained braced RC frames with a guaranteed hinge position.The specimen was one-half scale, assuming a high-rise RC building. The longitudinal rebars at the end of the beam were arranged in two layers, and the hinge position was separated from the beam–column joints by cutting off the longitudinal rebars in the second layer in the middle of the span. The RC frame and BRB were joined by a gusset plate installed on the beam. The yield axial force of the BRB was set such that the horizontal component was equivalent to the yield strength of the RC frame. Two specimens were used, and the presence or absence of de-bonding of the beam longitudinal rebars on the side where the moment was smaller than the assumed hinge position was used as a parameter. For loading, a horizontal force was applied, while an axial force was applied to the column.From the test results, in the specimen with de-bonding of the beam longitudinal rebars, the damage to the beam could be concentrated near the cutoff position of the longitudinal rebars, and a spindle-shaped restoring force characteristic was obtained. However, the story shear force decreased by approximately 30 % compared with the specimen with bonded beam longitudinal rebars. This is because the tensile force of the tensile longitudinal rebars is small in the de-bonded section.Next, a finite element analysis was performed to reproduce the two test specimens. In addition, to improve the decrease in story shear force of the specimen with de-bonded longitudinal rebars, a model in which the longitudinal rebars of the center of the span were fixed was analyzed. It was confirmed in the analysis that the decrease in the story shear force of the model