| Results from three plane frame joint specimens with rectangular column and another three joint specimens with circle column are presented in this thesis. These joint specimens are designed according to Code for Design of Concrete Structures (GB50010-2002) and tested under reversed cyclic loading with high axial load ratio and high shear-compression ratio. The objects of the experiments were to study the seismic performance of the joints influenced by axial load ratio with high shear-compression ratio, the law of bond and slip of the beam bar through the joints, the stress of the level stirrup legs and hysteretic dissipated energy and the law of the degrade of rigidity of the specimens. The details concerned and corresponding main results are as following: ①　The validity of the upper limit of the horizontal joint shear stress, which is suggested in existing codes, is verified according to the test results from joint specimens with rectangular column. These joint specimens work with high axial load ratio and high shear-compression ratio. ②　The feature of bond and slip of the beam bar through the joint has great influences on the specimen's seismic performance a lot. It is clarified how the axial load ratio,shear-compression ratio and deformation of the beam-column assemblage influenced the bond of the beam bar. The relation of displacement ductility factor μ?, axial load ratio n, shear-compression ratio v and average bond stress of the reinforcements are quantified on the basis of early research. ③In the condition of high shear-compression ratio, the ductility performance of the beam-column assemblage deteriorates with the increase of axial load ratio. Therefore, extra joint stirrups should be applied with the increase of the axial load ratio besides the stirrups calculated by seismic shear equation in existing codes. ④　The constraint factor ?j, which is suggested in shear equation of the joint to reflect the constraint of the cross beam to the joint, should not exceed 1.2 in any condition. ⑤In circle column, the length of the reinforcement through the joint is different due to the different location of the reinforcement, but all reinforcements bear loads synchronously and develop their tension capacity fully. It is suggested that the diameter of the beam bar db should be no more than D/25 to ensure better co-work ability. ⑥In the almost same condition, the action of joint stirrups in circle and rectangular columns are compared in different stages of the test. In early stage, the shear force is transferred mainly by the truss mechanism, the hoops in circle columns show weaker shear resistance ability than rectangular stirrups in rectangular columns. In late stage of the test, when the assemblage deformed severely , the bond action of the beam bar deteriorated and the action of the truss mechanism degenerated, hence the hoops confined the joint concrete much better than the rectangular stirrups did. ⑦Based on the test results from seven joint specimens with circle column, questions in seismic shear equation of circle column joints in existing codes are pointed out and new equations are presented in this thesis. It makes it possible to improve seismic shear equations of circle column joints in existing codes. |
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