Study On Compression Behavior Of Foamed Concrete-filled Cold-formed Thin-walled Steel Columns

Light steel-lightweight concrete structure is a new type of industrialized residential structure system,which is formed by the light steel frame outer wall panel and the light concrete inlaid inside.Compared with the traditional cold-formed thin-walled steel composite,due to its features of reasonable structure,light weight,high strength,energy saving,environmental protection,better thermal and sound insulation property,better fire-resistance property.It has been gradually applied in low-rise and mid-rise industrial buildings.However,previous studies have shown that:foamed concrete-filled cold-formed thin-walled shear wall cold-curved thin-walled steel-foamed concrete shear wall,as a type of light steel-lightweight concrete structure has a failure mode mainly manifested in the partial buckling failure of the wall end column,and the bearing capacity of the end column is one of the main factors affecting the seismic performance improvement of the shear wall.Therefore,it is of great significance to study the axial bearing capacity of wall end columns in order to avoid the reduction of shear wall bearing capacity due to its premature buckling failure.So,the seismic behavior of monolithic precast foamed concrete-filled cold-formed thin-walled steel columns were investigated by experiments,finite element numerical analysis and theoretical analysis,and the primary research works and research results are as follows:(1)Three of hollow cold-formed thin-walled steel columns and nine foamed concrete-filled cold-formed thin-walled steel columns were tested under axial compression to assess the failure phenomenon and process.The effects of foam concrete dry density,aspect ratio and slenderness ratio to specimen’s bearing capacity,stiffness and ductility were analyzed.Test results show that:The failure modes of the foamed concrete-filled cold-formed thin-walled steel columns are mainly the outward local buckling appeared near the height section,different from the hollow cold-formed thin-wall steel columns,the failure mode of the steel web and flange at the top of the column mainly occurs in the plane(including outward and inward)distortion buckling deformation failure.The foamed concrete-filled cold-formed thin-walled steel columns of the ultimate bearing capacity stiffness,displacement ductility better than hollow cold-formed thin-walled steel columns;The ultimate bearing capacity,stiffness and displacement ductility of foamed concrete-filled cold-formed thin-walled steel columns increased with the increase of dry density of the filled foam concrete and aspect ratio,but it is disadvantageous to increase the slenderness ratio.(2)The foamed concrete-filled cold-formed thin-walled steel columns were analysis with nonlinear finite element soft-ware ABAQUS.Their failure mode,stress process,load-displacement curve,stress strain curve and stress distribution were obtained.The results show that:The finite element model is agreed well with the test results in failure mode,load-displacement curve and ultimate bearing capacity;The cold-formed thin-walled steel is not fully utilized during the compression process;In the elastic stage,the vertical force is mainly borne by the cold-formed thin-wall steel and the foamed concrete;During the yield stage,the load of the foamed concrete begins to increase;At the peak stage,the cold-formed thin-wall steel and the foamed concrete buckle and fail outwards appeared near the mid-height section,and the foamed concrete and the cold-formed thin-wall steel bond and slip;During the failure stage,the cold-formed thin-walled section steel and the foamed concrete have shown significant separation in the buckling position.(3)Based on the results of finite element calculation of foamed concrete-filled cold-formed thin-walled steel columns,the mechanical mechanism of axial compression performance of the column is analyzed.The cold-formed thin-walled steel and the foamed concrete bear the axial load of the column,and their mutual restraint and enhancement.Firstly,the steel has a gripping effect on the foamed concrete,which changes the stress state of the foamed concrete,gives full play to its compressive performance,and improves the vertical bearing capacity of the foamed concrete;Secondly,the foamed concrete can restrain the cold-formed steel,strengthen the lateral support of the cold-formed steel,make its compressive performance play a greater role,and improve the vertical bearing capacity of cold-formed steel.(4)Based on the finite element simulation results of the thin-wall steel-foamed concrete column with cold bending,the schematic diagram of the stress region division of the columns on the cross section at the failure position is obtained.And the strain value distribution diagram of cold-formed thin-walled steel cylinder under the peak load of the upright column,and then the strength enhancement coefficient of cellular concrete and the reduction coefficient of cold-formed thin-walled steel material are determined respectively.Finally,the calculation formula of normal section axial bearing capacity of cold-formed thin-wall steel-foamed concrete column is established,and the calculated value is in good agreement with the experimental value of the specimen in chapter and the parameter analysis simulation value in chapter.