Research On Mechanical Behavior Of A New Multiple Concrete Filled Steel Tube Column-Beam Joints

Concrete filled steel tube structure is formed by filling concrete in steel tube,it can bear the external load by steel tube and its core concrete together.One kind of Multiple concrete filled steel tube(MCFT)structure in which circular tube was embedded inside the square steel tube,composing of an outer square steel tube and an inner circular steel tube,and pour concrete in the inner steel tube and between the two steel tube.At present,the MCFT structure is mostly used for columns,which is combined with steel beam or reinforced concrete beam to be used in building structure.However,the research and application of concrete filled steel tube beam-column combined into a whole structure are rare.In this research,based on the research direction of modern concrete-filled steel tube(SCFT)and the research results of MCFT joints,a New type of MCFT column-SCFT beam joint structure was proposed.The mechanical properties and failure modes of three kinds of combined structure joints of MCFT column-steel beam joint,MCFT column-SCFT beam joint and SCFT column-SCFT beam joint were compared and analyzed.Specifically include the following aspects.Based on the existed composite structure of SCFT column-steel beam joint test,the seismic behavior of the MCFT column-SCFT beam joint under low cyclic load was analyzed by finite element software ABAQUS.The result shows that the failure mode,skeleton curve and hysteresis curve of the established finite element model are in good agreement with the experimental results,which verify the rationality of the established model.On the basis,the beam-column cross-sectional dimensions of the New MCFT column-SCFT beam joint and SCFT column-SCFT beam joint were calculated.The mechanical properties of three kinds of combined structure joints of MCFT column-steel beam joint,MCFT column-SCFT beam joint and SCFT column-SCFT beam joint were analyzed under unidirectional load.The calculation results showed that compared to SCFT column-SCFT beam joint and MCFT column-steel beam joint,the beam end bearing capacity of MCFT column-SCFT beam joint is increased to a certain degree.The seismic performance analysis of three kinds of combined joints under low cyclic load were completed further.Three types of composite structural joints were compared with the seismic indexes of hysteresis curve,skeleton curve,stiffness degradation and strength degradation.The MCFT column-SCFT beam joint showed higher energy dissipation capacity,Compared with the joints using the MCFT column and the I-beam,the SCFT column-SCFT beam joint also showed some energy-dissipating advantages.The seismic performance analysis of the joints of MCFT column-SCFT beam joint and SCFT column-SCFT beam joint under low cyclic load was completed with the change of different axial compression ratio,concrete strength and connector size parameters.The analysis result showed that the change of axial compression ratio had a greater degree of impact on the seismic performance of two kinds of structural joints.There was less effect on the seismic performance of two kinds of structural joints of the change of concrete strength and the connector size.