Some observations on the local instability of orthotropic structural sections

Extract

The local buckling behaviour of structural sections composed of isotropic flat plate elements is well documented. The results are most conveniently presented in the form of curves for the minimum buckling coefficient, K_min, against the flange/web ratio λ₂. A series of such curves for a range of structural sections composed of orthotropic plates subjected to uniform end loads and simply supported end constraints has been presented by the author. For isotropic sections of practical proportions, it is generally assumed that the buckling coefficients for columns with simply supported and built-in end conditions approach the common value K_min, and that the half wavelength of the buckle mode in the axial direction is of the same order as the cross-sectional dimensions of the column. For structures composed of highly orthotropic materials such as carbon fibre reinforced plastic (CFRP), the half wavelength is much greater than that of the isotropic counterpart. In consequence, it is only for much longer sections that the common value of K_min, can be assumed for the buckling coefficient of built-in orthotropic sections without excessive error.