This paper intends to offer an alternative approach for deriving the buckling differential equations and boundary conditions of a straight I‐column subjected to various loads. Regarding a uniformly thin‐walled I‐column as an assembly of three flat plates (two flanges and one web) and modeling each of the plates as a Bernoulli‐Euler beam with narrow rectangular section, one can represent the nonlinear virtual work equation of the I‐column in terms of Yang and Kuo's nonlinear beam theory. Based on the geometrical hypothesis of rigid section, the buckling differential equations and boundary conditions of an I‐column subjected to various loads can be derived from the total potential equation presented herein by variational principle. Moreover, since the instability effect due to bi‐moments has been included in the flexural buckling equations, the buckling load of cantilever I‐columns subjected to compression and bi‐moment should be reduced for columns with lower torsional rigidities and fewer ratios of principal flexural rigidities.
Journal of the Chinese Institute of Engineers=中國工程學刊 30(4), pp.569-578