Residual Stresses and Tubular Compression Members

A computer study of concentrically loaded tubes shows that the strength reduction reaches 40% when the residual stress in the corner is at the compressive yield point of the elastic-plastic material. For members loaded with an eccentric axial force causing bending about the strong axis, the effect of residual stresses decreases as the eccentricity increases. Hence strength reductions of up to 40% are again possible for small eccentricities. The ratios of width or thickness to depth of the section have negligible influence on the magnitude of the residual stress effect. The residual stress pattern also influences the strength reduction when eccentrically loaded columns are free to buckle about the weak axis. This effect is most pronounced in narrow sections and increases as the load eccentricity increases. The classic interaction equation can be quite conservative in predicting unbraced beam column strengths when corners have a high residual tension.