Experimental Study on Horizontal Reinforcing Effects At RC Exterior Beam-Column Joints With Mechanical Anchors

Abstract eng:
Mechanical anchors are generally used to terminate the beam longitudinal bars at an exterior beam-column joint of reinforced concrete high-rise buildings in Japan. In the case of applying mechanical anchors compared with standard 90degree hooks, though development length could be shorter, cracks tend to concentrate around the anchor plates. When their cracks expand, the strength and ductility of frame decreases, thus the anchor failure should be avoided. In this study, for the purpose to develop a new reinforcing method to prevent not only the cracks concentrating around the anchor plates but also the diagonal cracks to spread at the center of beam-column joints panel, the tests of the half-scale exterior beam-column joints was conducted. Parameters of these tests were the placement of the horizontal shear reinforcement and their amount in the exterior joint. Concrete compressive strength was 45N/mm2, yield strength of longitudinal bar was 490N/mm2, and that of horizontal shear reinforcement was two kinds of 295 N/mm2 and 785 N/mm2. In addition, all of the test specimens were designed to be damaged at the area of beam-column joints, in reference to Dr. Shiohara studies [1~3]; column to beam bending strength margin was set to be less than about 1.5. In the basic specimen #1, horizontal reinforcement at the joint was placed uniformly, and in the specimen #2, additional concentrated horizontal reinforcement was arranged at the column side of the beam longitudinal bars. In the specimen #3, additional concentrated horizontal bars were placed at the center of the joint panel. In the specimen #4, they were placed at the joint side of the beam longitudinal bars. In the specimen #5, additional horizontal reinforcement was placed as half amount as in #4. From the test results of #1, after the maximum strength at about story drift of 1/50, the cracks at the beam-column joints expanded and the strength gradually decreased because of the joint bending failure. The reinforcing effect was largest in the #3, so the maximum strength was improved about 25% compared with #1, and it had maintained the strength until at the story drift angle of 1/15, also beam bending failure mode was remarkable. The maximum strength of #4 was equivalent to #3, but the strength decreased remarkably. The maximum strength of #5 was improved about 10%, but #2 was about 5% only. Consequently, the horizontal reinforcement at the beam-column joints effects on the strength of the joint bending failure and anchor failure, and the additional horizontal reinforcement near longitudinal bars at the joint are also very effective for increasing the maximum strength and ductility.

• Export as: BibTeX | MARC | MARCXML | DC | EndNote | NLM | RefWorks
• Add to your basket