Study On Mechanical Properties Of Concrete-filled Square Steel Tubular Beam Column Joints With CFRP Circular Tube

The composite structure of concrete-filled steel tube with CFRP circular tube is a new type of structure formed on the basis of two structures of concrete filled steel tube and CFRP tube reinforced concrete.This new type of composite structure is the combination of CFRP and concrete filled steel tube,it can be the characteristics of carbon fiber with high strength into full play,and can make up for the concrete filled square steel tube and CFRP tube defects of reinforced concrete structure with each other,and to further strengthen the internal concrete constraints,improve the bearing capacity and ductility.In recent years,researchers have studied more about their columns,but the research on beam column joints is relatively few.Therefore,it is necessary to study the concrete-filled square steel tubular joints with CFRP circular tubes.The object of this paper is the concrete-filled square steel tubular beam column joint with built-in CFRP circular tube.Through the two methods of experiment and finite element analysis,the mechanical properties of the object are analyzed.Experiments with CFRP tube diameter and force transmission plate length is variable,we designed three groups of specimens,and the paper introduced the production and loading of specimens,the results obtained with the observed failure modes,the test results of drawing the load displacement curve and the corresponding strain gauge load strain curve,on the basis of analysis,in order to get the relevant conclusions of the mechanical properties of specimens.In this paper,the three-dimensional model of the specimen is established by ANSYS finite element software.The process and principles of selecting unit and material property,modeling and solving criterion are introduced,and the finite element and experimental results are compared and analyzed.The results show that the force law and the test result obtained within the reasonable error range can be proved by the modeling method in this paper.Therefore,the accuracy of the modeling method in this paper is good.On this basis,this paper also use the software,the axial compression ratio,steel ratio,force transmission component size and other parameters of the expansion of the analysis,to compensate for the limited testing conditions,to set parameters less defects,more comprehensive analysis of the composite structure of the node in the force characteristics of different parameters under the.According to the results of the test and the finite contrast analysis,the following conclusions can be obtained.1)With inner CFRP circular beam column node and square concrete filled square steel tube beam column joints,not much difference between the ultimate bearing capacity can bear,this is because in the case of small axial compression,CFRP circle does not give full play to the confinement effect of core concrete pipe,so the existence of CFRP round tube,on the ultimate bearing capacity of the joint had no obvious effect,but the set of CFRP tube,concrete will be extended to a certain extent,flexible working period,improve the anti instability capability of the whole structure;2)The failure modes of the nodes obtained by the two research methods are plastic hinge on the weld seam of H steel beam and load transfer steel beam,resulting in failure of specimens,which is consistent with the requirements of "strong column and weak beam".3)Increasing the length of the transmission steel plate will significantly improve the ultimate bearing capacity of the nodes,but it will also seriously affect ductility and make the structure brittle failure.Therefore,when designing the structure,we must consider both ductility and bearing capacity,so we can not simply pursue the maximization of one side.4)The change of the diameter of the CFRP tube has no obvious influence on the load-displacement curve of the node,and the ultimate bearing capacity is almost invariable.5)The change of axial compression ratio has no obvious influence on the ultimate bearing capacity of the joint,but the ductility of the joint will decrease with the increase of axial compression ratio.6)Increasing the yield strength of steel will increase the ultimate bearing capacity of the joints significantly,and also improve the ductility.7)The change of concrete compressive strength has little influence on the ultimate bearing capacity of the joints.