only consider the effect of slenderness ratios Although the CFST is set in the composite column when the steel pipe diameter to thecolum ng moment.To make sure there are certain reserves,fully axial compression bearing capacity can't be used,therefore limit the axial pressure.The reduction coefficient can be taken as 1.0 because of the RC outside 4.Equivalent calculation length.Composite column's equivalent length is calculated in accordance with the relevant provisions of the CECS28-90.Both of the two consider the constraint condition and bending moment distribution gradient effect. Table 2 comparison of axial compression capacity of CFST with the CFST in composite column types CFST column CFST in composite column Axis pressure N≤N, N≤0.9N design value Axial N。=0.9p,9.A.∫1+fe) N.=9f.A1+1.80) capacity reduction 9,=1-0.115L./D-4, 9=1-0.1150.1d。-4)2, coefficient(sl (L.1D>4) l.1d。>4) enderness ratio) 9,=1L./D≤4 9=1.0,1.1dn≤4 1 reduction 9.=1+1.85eo1m. e/r.≤1.55 without consideration 0.3 ratio) p。= %1g-041>1.5S Equivalent atio L。=k .=H length Note:L-the actual length of the column:H-length of the cantilever column Table3 comparison of axial compression capacity of CFST with composite column CEST column composite column axial N.=0.9g,,Af.1+f(0)N=0.9p(fAm+fA.)+fnA1+1.80 n capacity L。=kL Bottom columns:1.0H,others:125H Note:H for the bottom column can be taken the height from foundation top face to the first layer,H for the others each laver can be taken the height between the two top of the floor laver. Both the concrete inside and outside contribute the composite column axial compression capacity.and the interior CFST reduction coefficient is taken as 1.0.So the bearing capacity ofonly consider the effect of slenderness ratios. Although the CFST is set in the composite column section center, mainly carrying axial compression, but when the steel pipe diameter to the column section side length ration is large, the CFST should bear the a small amount of bending moment. To make sure there are certain reserves, fully axial compression bearing capacity can’t be used, therefore, limit the axial pressure. The reduction coefficient can be taken as 1.0 because of the RC outside 4. Equivalent calculation length. Composite column’s equivalent length is calculated in accordance with the relevant provisions of the CECS28-90. Both of the two consider the constraint condition and column bending moment distribution gradient effect. Table 2 comparison of axial compression capacity of CFST with the CFST in composite column types CFST column CFST in composite column Axis pressure design value N  Nu Ncc 9Nu  0. Axial pressure bearing capacity N 0.9  A f (1 f ( )) u  l e c c  (1 1.8 ) Nu  1 f cc Acc   reduction coefficient(sl enderness ratio) ( / 4) 1 0.115 / 4     L D L D e l e ， l  1，Le / D  4 ( / 4) 1 0.115( / 4) 1/ 2 1     e a e a l d  l d ， 1  1.0，le / da  4 reduction coefficient （eccentricity ratio） / 1.55 1 1.85 / 1 0 0    c c e e r e r  ， / 1.55 / 0.4 0.3 0 0    c c e e r e r  ， without consideration Equivalent calculation length Le  kL le  H Note: L-the actual length of the column; H- length of the cantilever column. Table 3 comparison of axial compression capacity of CFST with composite column types CFST column composite column axial compressio n capacity N 0.9  A f (1 f ( )) u  l e c c   0.9(   )  (11.8 ) u co co y ss cc Acc N f A f A f effective length Le  kL Bottom columns：1.0H，others：1.25H Note: H for the bottom column can be taken the height from foundation top face to the first layer, H for the others each layer can be taken the height between the two top of the floor layer. Both the concrete inside and outside contribute the composite column axial compression capacity, and the interior CFST reduction coefficient is taken as 1.0. So the bearing capacity of composite column of is higher than that of CFST column