Comparison of two approaches for checking stability capacity of steel frame columns

First,two steel frames with geometric imperfections are built,the ultimate load of these frames Pcr and Hcr under horizontal and vertical load are got through finite element analysis.Then use the ultimate load Pcr and Hcr to calculate the internal force of the same two frames without geometric imperfections through the way of first-order analysis and second order analysis.Then get the nominal stress of the column using the formula of the ultimate load capacity of bending-compression members in steel structure design code in current use in our country(GB50017-2003),and compare it with the real stress.It proves that when using the formula of the ultimate load capacity of bending-compression members to check the stability of columns,using the second order elastic analysis to calculate the internal force of the frame and choosing the real length to be the effective length of the column,the result is better and safer than that through the way of using the first order elastic analysis to calculate the internal force of the frame and choosing the elastic buckling length to be the effective length of the column.