Local Stability of Filled and Encased Steel Sections

Abstract

The buckling of the component plates of structural sections may be avoided by ensuring that their breadth-to-thickness (bit) ratios are less than the specified limit for the prevailing loading condition. Limiting bit ratios apply to plates that are free to buckle onto either side of their initial plane. For sections that are filled or encased with concrete it is likely that the component plates can only buckle away from the interface with this material. The derivation of bit ratios for this class of plates is presented in this paper. The energy method is used to equate the work required to load the plate, to the work required to deform the plate into a buckled shape. Orthotropic plate theory and the flow theory of plasticity are used to evaluate bit ratios for plates subjected to uniaxial compression, combinations of bending and axial loading, and shear. The resulting bit ratios are higher than those for plates not restrained by intimate contact with concrete. The benefits of using infilling or encasement to improve the structural behavior of steel sections are also discussed. © ASCE.