International Concrete Abstracts Portal

As part of a United States/New Zealand/Japan/China collaborative research project, interior and exterior beam-column joint subassemblages with floor slabs of prototype two-way and one-way reinforced concrete building frames were designed for earthquake resistance using the current New Zealand concrete design code, NZS 3101:1982. Three full-scale subassemblages as designed were constructed and tested under quasi-static cyclic loading which simulated severe earthquake actions. The overall performance of each subassemblage during the tests was satisfactory in terms of strength and ductility. The joint core and column remained essentially undamaged while plastic hinges formed in the beams. The strong column-weak beam behaviour sought in the design, desirable in tall ductile frames designed for earthquake resistance, was therefore achieved. Although the joint cores of the subassemblages remained in the elastic range, joint core shear deformations contributed significantly to the interstorey drifts. Also, a significant proportion of the slab bars in tension contributed to the negative moment flexural strength of the beams. The performance of the one-way joint was superior to the performance of the two way joints.

SP123 This volume is a collection of technical papers on the aspects of design of beam-column joints for seismic resistance. Nineteen papers are divided into the following groups. - Tests conducted on specimens designed using current codes but with the same general geometry and a specified loading history. (4 papers) - Design recommendations -- Japan. (1 paper) - Influence of joint geometry on strength and deformation characteristics. (8 papers) - Influence of bond on joint performance. (4 papers) - Joint in precast systems and with high-strength materials. (2 papers)

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.