Study On The Connection Of The Circle Section Inner And Square Section Outer Concrete-filled Twin Tubes To The Composite Beam

Concrete-filled twin steel tubes columns like ordinary steel columns have advantages of high bearing capacity,good ductility,good fire resistance and convenient construction.At the same time,it also has the advantages of neat and beautiful appearance and simple structure,and is suitable for wide application in engineering.Concrete-filled twin steel tubes column connections serves as the transfer hub of frame structure,and some scholars have done some research on this kind of new type of connections which shows that the new type of connections have good mechanical properties.In current study of the seismic behavior of the connections,the influence of the reinforced concrete floor on the mechanical behavior of concrete-filled twin steel tubes column connections under cycle loading is not clear.It is necessary to research the new type connections,and investigate their behaviors under seismic load and establish the design methods.In this dissertation,four connections of the circle section inner and square section outer concrete-filled twin tubes to the composite beam and one connection of the circle section inner and square section outer concrete-filled twin tubes to the steel beam were designed.Also the means of experimental tests and numerical simulation were adopted to analysis the seismic behavior of different types of connections.The main work in this dissertation is as follows:(1)In this dissertation,four connections of the circle section inner and square section outer concrete-filled twin tubes to the composite beam and one connection of the circle section inner and square section outer concrete-filled twin tubes to the steel beam were tested under the low cycle loading with constant axial compression ratio,and the failure characteristics of the new connections were analyzed.(2)The seismic behavior,the hysteretic curve,the skeleton curve,the ductility,the energy dissipation capacity,the strength and stiffness degradation were analyzed.The test results show that the hysteretic curves of the connections are full,which proves that the connections perform well in ductility and energy dissipation,and the connection strength and the stiffness degradation is stable.(3)The skeleton curves and the failure modes of the connections from the results of the numerical simulation were compared with the tests results.The results show good agreement which has confirmed the finite element model accuracy effectively.In the end,the joints stress were analyzed to confirm the force transfer mechanism.At the same time,the influences of axial compression ratio and concrete strength on the behavior of the connections were studied.