International Concrete Abstracts Portal

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)

Describes two types of prefabricated beam-column joints designed to save manpower requirements in construction work. The first type consists of making precast subassemblages with beam-column joints and integrated beams. Through-holes are provided in the vertical direction in the beam-column joint to accommodate column reinforcing bars (Type 1). The second type consists of precast subassemblages with beam-column joints and columns integrated. Through holes are provided in the horizontal direction in the beam-column joint to accommodate beam reinforcing bars (Type 2). Column or beam reinforcing bars are passed through the holes in these precast subassemblages; the parts are integrated by subsequent grouting of the holes with high-strength mortar. The earthquake resistance of these precast subassemblages was investigated with cyclic loading tests. The systems are intended for use in a 13-story reinforced concrete building, designed so that its collapse mechanism would be of the beam-yielding type. With Type 1 precast subassemblages, column reinforcing bars grouted and fixed inside sleeve-pipe holes are not subject to stresses extending into the plastic range. Therefore, by suitably designing the anchorage lengths of beam reinforcing bars inside the joints, there will be no slippage of the beam bars. A ductility of more than six times the yielding displacement may be attained. With Type 2 subassemblages, the beam reinforcing bars grouted and fixed inside sleeve-pipe holes are subjected to repeated stresses extending into the plastic range, such that bond deterioration occurs inside the joints. Strength declines at large deformations exceeding three times the yield displacement, and satisfactory ductility is not obtained. Taking test results into consideration, precast subassemblages of the first type are recommended for adoption in the 13-story building.

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.