SHEAR STRENGTH OF SRC BEAM-TO-COLUMN JOINTS WITH CONCRETE FILLED SQUARE TUBULAR COLUMN

Concrete filled tubes (CFT) are commonly used for high-rise buildings and encased in reinforced concrete (RC) at the basement floor in Japan. Recently, CFT with RC encasement tends to be used for structural columns of high-rise buildings in China as well. However, for example, when T-shaped RC encasements are covering steel frames at the joints from the ground to the basement floor, the structural behavior of the beam-to-column joints is too complicated; thus it is difficult to evaluate the shear strength under seismic forces. In other words, it can be said that evaluating the shear strength of the beam-to-column joints is currently unclear because of a lack of experimental investigations. Therefore, a systematic experimental study to investigate the application of the previous evaluation method for shear strength of steel beam-to-CFT column joints with RC encasement is addressed in this paper. First of all, the previous evaluation methods in AIJ standard for structural calculation of SRC structures and in AIJ recommendations for design of Steel and CFT structures were summarized. Based on these investigations, the evaluation method composed of each component is rearranged. And then, a cyclic loading test of beam-to-column joints was conducted to verify the application of this evaluation method. The test specimen is beam and column subassemblies designed to realize weak beam-to-column joints. Three pairs of specimens were tested. The first two pairs consisted of a rectangular hollow section and that with filled concrete. The third pair has T shaped RC encasements to represent the joint from the ground to the basement floor and consisted of different length of mechanical anchorage for column longitudinal reinforcements at the beam-to-column joint. The test results can be summarized as follows: (1) an increment of stiffness and strength by the presence of concrete infilled and RC encasement were observed in experiment; (2) the influence of different mechanical anchorage length on overall behavior of beam-to-column joint from the ground to the basement floor was few, but the strength was reduced to 2/3 of that of the SRC frame; (3) at the load level of 1/ 100 rad of story drift ratio, the residual crack on surface of the beam-to-column joint was roughly 0.2 mm which is small enough to realize damage prevention under earthquakes; (4) the experiment results indicate that the evaluation method enables to predict plastic strengths of each component.