Study On Axial Compression Performance Of Concrete-filled Square Steel Tube Short Columns With Transverse Diaphragm

Concrete-filled steel tube(CFST)giant column is an important stress component in super tall buildings and has been applied in practical engineering.This type of column section usually has multiple cavities with complex longitudinal and transverse structural measures,whereas a single cavity of a giant column has a mechanical behavior similar to that of a square(moment)CFST column.This paper intends to explore the influence of diaphragms on the mechanical performance of giant columns under axial compression.With diaphragms thickness and spacing as parameters,five concrete filled square tubular short columns were designed and tested for axial compression performance.The failure modes,load displacement curves and bearing capacity of different specimens were obtained.Data analysis shows that the constraint effect of steel tube on core concrete can be strengthened by setting diaphragm,which is reflected in the load displacement curve and failure mode.Reasonable control of the thickness and quantity of the diaphragm can effectively improve the transverse binding force of the steel tube on the core concrete and improve the bearing capacity and ductility of the specimen.Using nonlinear finite element software ABAQUS,finite element modeling of concrete filled square steel tube short column with diaphragms is carried out.Concrete uses C3D8 R solid element,and diaphragms and steel tubes use S4 R solid shell element.The Han constitutive model is adopted for concrete and the influence of the constraint effect of the diaphragm is considered.The ideal elastic-plastic model is adopted for steel.The plastic strain-damage factor curve is constructed for concrete based on Najar damage theory.The numerical simulation results show that the constitutive relationship of concrete and steel is reasonable,which can basically reflect the results of load-displacement curve and failure mode.The stress analysis shows that with the increase of the thickness and number of diaphragms,the effective restraint area of concrete increases,and the constraint of steel tube on concrete increases.Parameter analysis shows that strengthening concrete strength,steel pipe strength and steel pipe wall thickness can effectively improve the bearing capacity of members.Based on the Mander model and the failure criterion of Guo-Wang concrete,the calculation method of bearing capacity of concrete-filled steel tubular columns with diaphragms is explored,and the calculation formula of bearing capacity is given.The calculated results are not different from the experimental and finite element simulation results,which provides a reference for the design of similar components.