Study On Axial And Eccentric Compression Mechanical Properties Of Rectangular Concrete-filled Steel Tube Stub Columns With Inner Confined Elliptical Stirrups

Compared with circular CFST column and square CFST column,the constraint effect of steel tube on core concrete in rectangular CFST column is insufficient,the steel tube is prone to local buckling,and the bearing capacity and ductility are relatively poor,which greatly limits the practical application of rectangular CFST column.In view of the above problems,this paper puts forward an improved section form of rectangular CFST column,rectangular CFST column with inner constrained elliptical stirrups.The bearing capacity and ductility of rectangular CFST column are improved,which provides theoretical support and scientific basis for the practical application of this kind of column.This article mainly carries out the following work:1.The axial compression performance tests of 8 rectangular CFST columns with inner confined elliptical stirrups,1 rectangular CFST short column with inner confined rhombic stirrups,1 rectangular CFST short column with inner confined rectangular stirrups and 5ordinary rectangular CFST short columns were carried out.The results show that:(1)when the total amount of steel is the same,the axial compressive bearing capacity and ductility of the rectangular CFST short column with elliptical stirrups are improved compared with that of the ordinary rectangular CFST short column;(2)reducing the spacing of stirrups or increasing the diameter of stirrups,the axial compression bearing capacity of the rectangular CFST short column with elliptical stirrups is improved,and the effect of reducing the stirrups spacing is better;(3)the larger the ratio of length to width of rectangular steel tube,the smaller the axial compressive bearing capacity and ductility of the rectangular CFST short column with elliptical stirrups;(4)the axial compressive bearing capacity of rectangular CFST short columns with elliptical stirrups is larger than that of rectangular CFST short columns with rhombic stirrups and rectangular CFST short columns with rectangular stirrups.Combined with the analysis of steel quantity,it can be seen that the benefit of rectangular concrete filled steel tube short column with elliptical stirrups is better than that of inner rhombic stirrups and inner rectangular stirrups.2.The test on the bias compression performance of 6 rectangular CFST columns with inner confined elliptical stirrups and 3 ordinary rectangular CFST columns is carried out.The effects of the spacing of stirrups,the diameter of stirrups section and eccentricity were investigated.The results show that:(1)when the eccentricity is small,the bias bearing capacity of rectangular CFST short column with inner confined elliptical stirrups is larger than that of ordinary rectangular concrete short column with the same steel use;When the eccentricity is large,the bias bearing capacity of rectangular CFST short column with inner confined elliptical stirrups is smaller than that of ordinary rectangular CFST short column with the same steel use;(2)the ductility of rectangular CFST short column with inner confined elliptical stirrups is significantly better than that of ordinary rectangular CFST short column with the same steel use;(3)with the decrease of elliptical stirrups spacing,the bias bearing capacity and ductility of rectangular CFST short columns with internal confined elliptical stirrups are improved;(4)the effect of increasing the cross-section diameter of elliptical stirrups on the bias bearing capacity of rectangular CFST short columns is poor,but the ductility of the members can be significantly improved.3.Based on the finite element analysis software ABAQUS,a three-dimensional finite element model of rectangular CFST short column with inner confined elliptical stirrups under axial and bias compression are established.The results of finite element analysis are in good agreement with the test results.The influence of various factors on the axial compression and bias compression mechanical properties of rectangular CFST short column with inner confined elliptical stirrups is analyzed.Based on the results of test and parameter analysis,the calculation formulas of axial compression bearing capacity and bias compression bearing capacity of rectangular CFST short column with inner confined elliptical stirrups are put forward.The calculation formula has good accuracy in general and can meet the design requirements of practical engineering.