| A tubed RC column with high longitudinal reinforcement ratio (TRC-HLRR) is a RC column confined with a thin steel tube. TRC-HLRR is a new type of composite columns that the steel tube disconnects in the beam-column joints. Experimental research and theoretical analysis on TRC-HLRR beam-column joints under axial compression are conducted,to investigate the axial compression static behavior under static axial compression.A total of 18 TRC-HLRR beam-column joints and 4 stubs with the same cross section are designed and manufactured. The experimental parameters are shapes of the section, the types of joint-beams, the height of the beam-column joints and stiffeners for the square beam-column joints. The longitudinal reinforcement ratio of the circular specimens is 4%, and the square ones is 6.3%. The tube radius(width)-to-thickness-ratio of the all specimens is 133.The specimens are tested under static axial compression. The failure modes, load-displacement curves, load-strain and stress curves of the steel tube and concrete, are obtained during the test. The test results indicated that crush failure occurs in all circular beam-column joints. The axial compression bearing capacity of circular beam-column joints is about 15%~30% lower than circular stub columns. For the circular specimes, the axial compression bearing capacity increases with joint-beams numbers and decreses with the height of the beam-column joints, so the joint-beams can improve the axial bearing capacity of the circular beam-column joints.The crush failure occurs in the stub part of square beam-column joints. The axial compression bearing capacity of square beam-column joints is almost the same as the square stub columns. The axial compression bearing capacity of the square beam-column joints with stiffeners is about 10% higher than the normal square specimens. Therefore, the stiffeners can improve the confining effect of the square tube effectively.Axial bearing capacity formula of the TRC-HLRR beam-columns is buit through the the confined concrete model and joint-beams action. The predictive results compared fairly well with the test results. |
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