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Summarizes a series of research efforts at the University of Tokyo leading to the development of earthquake-resistant design criteria for reinforced concrete interior beam-column joints. The design criteria emphasize the protection of the joint to an acceptable deformation level of a frame structure during an intense earthquake. For the design against shear, shear-resisting mechanisms by truss and concrete compression strut, the role of joint lateral reinforcement, and the effect of transverse beams and slabs were studied experimentally. The requirement for beam bar bond was discussed on the basis of nonlinear earthquake response analysis.

The Architectural Institute of Japan (AIJ) published its 1988 draft design guidelines for earthquake-resistant reinforced concrete buildings based on ultimate strength concept as a first attempt to develop an ultimate strength design procedure in Japan. This paper introduces the general concept of the design procedure, and explains in detail the design requirements and background information for reinforced concrete beam-column joints of the AIJ guidelines. Based on experimental evidence, the amount of lateral reinforcement in the joint required is significantly reduced from ACI requirements.

Eight 1/3 scale specimens, consisting of four pairs of interior and exterior beam-column subassemblages in one-way frames, were tested. To investigate the basic joint shear strength, the test program was so determined that joint shear failure occurred in most specimens prior to beam yielding by using high-strength steel for beam bars. Test variables were beam bar strength, column axial load, and amount of joint hoop. The test results showed: 1) the increase of column axial load level from f'c / 12 to f'c / 4 did not influence the ultimate shear strength of the interior joints, but this increase in column axial load improved the shear strength of the exterior joints nearly 10 percent; 2) the ultimate shear strength represented in terms of nominal shear stress was f'c / 4 for interior joints; 3) when the shear strength of the exterior joints was evaluated on the basis of projected length of hooked beam bars instead of total column depth, nearly the same strength was obtained for both types of joint; 4) the increase of joint shear reinforcement ratio from 0.41 to 1.1 percent did not noticeably effect the behavior for both types of joint; 5) once joint shear strain reached to 0.5 percent degradation of shear rigidity was accelerated under subsequent load reversals.

Reversed cyclic loading tests were carried out for 18 reinforced concrete exterior beam-column subassemblages designed in accordance with the principle that yielding of adjoining beam or column precedes joint shear failure. Column axial force, amount of joint hoop reinforcement, existence of intermediate column bars, and moment-resisting capacity ratio of beam to column were selected as experimental variables. Test results showed that the ductility of the subassemblages increased by column axial compressive force and the amount of the joint hoop reinforcements. The existence of the intermediate column bars was also effective in increasing the ductility. On the basis of thorough consideration of the test results, a critical cumulative displacement ductility factor was quantified as a function of the test variables, and was ascertained to be a very effective value to evaluate the aseismic performance of exterior beam-column subassemblages.

Two series of experiments on the performance of beam-column joints in reinforced concrete frames were carried out. In Series I, the influence of the transverse reinforcement in the joint and/or the portion of the beam end connected to the column was investigated. From the test results, it is derived that heavy transverse joint reinforcement may reduce the slippage of beam bars in the joint and enhance the joint stiffness after cracking, and the similar transverse shear type reinforcement in the beam end has little effect on relieving the stiffness after degradation of a frame due to the deterioration of bond along the beam bars within the joint. In Series II, the effects of locating a plastic hinge in the beam away from the column face were examined. The test results show that the bond deterioration of beam bars within the joint may be prevented effectively by plastic hinge relocation, but shear-sliding deformation may occur at the plastic hinge away from the column face owing to the inevitable increased shear force in the beam. A new arrangement of beam bars to improve the behavior of the plastic hinge is proposed.