The paper focuses on overall and local web plate buckling of longitudinally multi-stiffened aluminium plate girders subjected to compression, bending, shear and transverse loading. The authors completed wide-range bifurcation stability analysis by energy method. Based on the results of the completed parametric study, buckling coefficients are formulated, taking also into account the possible interaction of local and overall buckling. Modifications are proposed for the standard Eurocode calculations of critical loads. Modification in resistance calculation for web crippling is also proposed to take the beneficial effect of curved flange-to-web connection into account. Numerical model is developed for nonlinear static analysis. Virtual experimenting – considering actual material behaviour and imperfections – is invoked for the calibration of the model.