Study on Ultimate Capacity of Steel H-Section Members Under Combined Biaxial Bending and Axial Force

The ultimate resistance of steel H-section members under biaxial bending and compression has been discussed in the present paper. Finite element models taking account of geometrical and material nonlinearities are established and validated by previous laboratory test results. A series of parametric studies are then conducted considering different loading angles and a spectrum of flange width-to-thickness ratios, web width-to-thickness ratios and axial force ratios. An improved energy inflection method (EIM), which is verified by comparing the analytical results with numerical results, is proposed in order to determine the ultimate state of the members under biaxial bending. It is shown that the ultimate state determined by EIM occurs when the sectional stress distribution reaches the envelop line. Finally, a simple interaction formula is proposed to predict the ultimate capacity of the steel H-section columns subjected to biaxial bending and compression. It is verified that the interaction formula can provide a satisfactory prediction, in comparison against the European code which tends to offer a relatively conservative estimate. The proposed method is applicable to flange width-to-thickness ratios ranging from 8 to 28, web width-to-thickness ratios changing from 30 to 120, and axial force ratios varying from 0 to 0.4.