The influence of strain-hardening on the ultimate behaviour of aluminium RHS-beams under moment gradient

In this paper, the influence of strain-hardening on the ultimate behaviour of aluminium beams made of rectangular hollow sections (RHS) and subjected to non-uniform bending is investigated by analysing different aluminium alloys. The strain-hardening behaviour is related to the Ramberg-Osgood exponent of the constitutive stress-strain law of the material. A wide parametric analysis has been accomplished referring to both cooled, heat-treated and naturally-aged alloys. The results of comprehensive regressions analyses fitting the results obtained from numerical FE models are presented. Therefore, the main outcome of the work is the proposal of empirical relations for the prediction of the ultimate behaviour of RHS aluminium beams, accounting for the flange slenderness, the flange-to-web slenderness ratio, the non-dimensional shear length and the Ramberg-Osgood exponent. The proposed mathematical relationships allow a quick estimation of the ultimate non-dimensional flexural resistance and both total and stable part of plastic rotation capacity.