| Steel-tube-confined concrete column is a new type of composite structure with high bearing capacity,good fire resistance and high ductility.Compared with traditional concrete-filled steel tubular column,its construction is more convenient.However,since the steel-tube-confined concrete pipe is disconnected at the beam-column joint,the concrete in the joint area is not effectively restrained,resulting in insufficient bearing capacity of the joint.It is even less restrained for the corner joint.At present,the problem of weak joints have not been solved by relevant strengthening measures for such joints.Therefore,further research is needed on the steel-tube-confined concrete beams-columns joint.Based on the existing research results,the axial compression behavior of four circular steel-tube-confined concrete beams-columns corner joint with steel rings reinforcement and one corner joint specimen without steel rings reinforcement were studied.In the test,the influence of the two parameters on the bearing capacity of the corner joint was studied by controlling the thickness of the steel ring and the longitudinal reinforcement ratio.The finite element software was used for the numerical analysis,and the influence of the beam end shear force and bending moment on the bearing capacity of the joint was considered in the numerical analysis.The main conclusions and results are as follows:(1)The existence of steel rings in the joint area has a great influence on the ultimate bearing capacity of the specimen.For the steel rings with thickness of 2mm specimen,the ultimate bearing capacity is 13.3% higher than that of the specimen without steel rings.For the steel rings with thickness of 3mm specimen,the ultimate bearing capacity is 42.9% higher than that of the specimen without steel rings.This indicates that the existence of steel rings can effectively improve the bearing capacity of joint specimens.In addition,the axial compression stiffness of specimens increases with the increase of steel ring thickness.(2)The ultimate bearing capacity of the specimen increases with the increase of the longitudinal reinforcement ratio for the same thickness of the steel rings.The specimen with the longitudinal reinforcement ratio of 2.67% is 0.5% higher than the specimen with the longitudinal reinforcement ratio of 1.85%.The specimen with longitudinal reinforcement ratio of 3.63% is 8.6% higher than the specimen with longitudinal reinforcement ratio of 2.67%.It is shown that the ultimate bearing capacity of the joints can be improved by properly enlarging the longitudinal reinforcement of the column section.(3)For the 3mm-steel ring with 1.5mm-steel tube,and the longitudinal reinforcement rate of the column section increases from 1.85% to 2.67%,the damaged area of the specimen is transferred from the joint part to the column part,indicating that the longitudinal reinforcement of the column section can effectively improve the mechanical performance of the joint with the steel ring is thickened.(4)Based on numerical analysis,while the shear force and bending moment are applied simultaneously on the joint beam,the ultimate bearing capacity of the specimen decreases with the increase of the shear force and bending moment,and the change rule is roughly linear.In general,the existence of beam end shear force and bending moment has a small impact on the axial bearing capacity of joints,with a difference of less than 3%.(5)Based on experimental research and numerical analysis,formula for calculating the bearing capacity of the reinforced joints under compression was established.The maximum error within 7%,the average error is only 3.7% by comparing the formula to calculate the theoretical results with the experimental results. |
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