Strength curves for metal columns

The paper explores a general approach to the design of columns of metallic materials, notably aluminum and stainless steel. The stress-strain curves of these materials, and metallic materials in general, are nonlinear. In the paper, the stress-strain curves are assumed to be expressed as Ramberg-Osgood curves, defined in terms of the initial modulus (E-0), the 0.2% proof stress (sigma(0.2)) and the parameter n. It is shown that the column curve can be expressed in terms of the Ramberg-Osgood parameters by adopting a Ferry curve as a basic strength curve and expressing the imperfection parameter in terms of E-0, sigma(0.2), and n. The proposed strength curves are compared with column strengths obtained using advanced finite-element analyses of square hollow-section columns. For a wide range of material parameters, the mean of the ratio of finite-element strength to column strength is calculated using results for a range of column lengths and shown to lie between 0.98 and 1.04. The coefficient of variation of the same ratio is shown to be less than 0.025 indicating that the proposed strength curves are in good agreement with the finite-element strengths.