Research On Mechanical Properties Of Composite Columns With High Strength Concrete Filled Steel Tube Flange And Honeycomb Steel Web After Freeze-thaw Cycle

With the development of the building system to the direction of large span,heavy load and super high,the traditional reinforced concrete structure can no longer meet the needs of modern buildings.Although the light steel structure system has many advantages such as light weight,short construction period and low price,its stability and fire resistance are poor and easy to corrode,prone to buckling deformation,resulting in structural instability and failure.In order to meet the needs of modern society for building structures in large span,super high,fire resistance,wind resistance,earthquake resistance and other aspects,concrete filled steel tube structure came into being.Concrete filled steel tubular（CFST）structures have many advantages,such as light weight,large span,strong bearing capacity,short construction period and good seismic performance.They are widely used in large span,super high-rise and heavy load structural systems.Combining the needs of modern buildings and the advantages of concrete-filled steel tubular structures,this paper proposes a new type of composite column:rectangular steel tube high-strength concrete flange honeycomb steel web composite column.The composite column is mainly composed of two rectangular steel tube high strength concrete columns connected by honeycomb steel webs.The steel tube can make the core concrete in a three-dimensional compression state,thereby improving the bearing capacity and stability of the column.The concrete can reduce or delay the local buckling of the steel tube and prolong the service life of the column.The use of honeycomb steel webs can not only make the building structure more beautiful,but also reduce the weight of the structure.It can be seen that this kind of composite column has broad application prospects in large-span,heavy-duty and super high-rise buildings.As we all know,building structures in severe cold regions are significantly affected by freeze-thaw action.Traditional reinforced concrete structures are prone to concrete spalling under freeze-thaw conditions,which seriously affects the performance and bearing capacity of structures.In order to ensure the popularization and application of the new frame structure proposed by the research group in severe cold regions,it is very important to master the mechanical properties of the new frame system under freeze-thaw cycles.In view of the fact that there are few studies on the mechanical properties of rectangular steel tube high-strength concrete flange-honeycomb steel web H-section composite columns after freeze-thaw cycles in the frame system,and the failure mechanism of such composite columns after freeze-thaw cycles is not clear,this paper studies the mechanical properties of rectangular steel tube high-strength concrete flange-honeycomb steel web H-section composite columns after freeze-thaw cycles.The main research work is as follows:1.Using the finite element software ABAQUS,based on the bilinear constitutive model of steel,the constitutive model of Hanlinhai confined concrete and the constitutive model of confined high-strength concrete under freeze-thaw cycle,the finite element models of rectangular concrete-filled steel tube flange honeycomb steel web composite short column and high-strength concrete-filled steel tube short column after freeze-thaw cycle are established.Through numerical analysis,the load-displacement curves of the existing test specimens are obtained.Compared with the test curves,the two are in good agreement,which verifies the accuracy of the finite element modeling method and the selection of the constitutive model.2.In order to study the axial compression performance of full-scale rectangular steel tube high-strength concrete flange honeycomb steel web composite column（STHHC）under freeze-thaw cycles,48 full-scale composite column specimens were designed with constraint effect coefficient（ξ）,concrete strength(f_cu),number of freeze-thaw cycles（n_d）,slenderness ratio（λ）,distance-height ratio（s/h_w）and hole-height ratio（d/h_w）as the main test parameters.The finite element analysis was carried out to obtain the load-displacement curve,section stress-strain curve,ductility and failure mode of the composite column,and the influence of different parameters on the axial compression performance of the composite column was clarified.The 1st Opt software was used to fit and regress the calculation formula of the axial compression bearing capacity of the STHHC composite column under freeze-thaw cycles.3.In order to study the seismic performance of STHHC composite columns under freeze-thaw cycles,60 full-scale specimens were designed with the main parameters of section steel ratio（α）,number of freeze-thaw cycles（n_d）,shear span ratio（λ_s）,axial compression ratio（n）,height-width ratio（D/B）,distance-height ratio（s/h_w）and hole-height ratio（d/h_w）.The numerical analysis of seismic performance of STHHC composite columns under different freeze-thaw cycles is carried out,and the hysteresis curve and characteristics of composite columns are obtained.The influence of different parameters on the skeleton curve,energy dissipation capacity,resistance attenuation and stiffness degradation of composite columns is clarified.Finally,the load-displacement elastic-plastic restoring force model of this kind of composite column is established and the corresponding engineering design suggestions are given,which provides theoretical basis and technical support for the popularization and application of this new type of composite column in severe cold area.