This paper describes the basic philosophy of the design aluminium structures according to the new European standard EN1999: Design of aluminium structures, Part 1-1: General structural rules. Comparison of the properties of aluminium as a material for structural elements is given in relation to the carbon steel. Special attention is given to the buckling effect in compressed parts of the cross section as well as the thermal effects of welding process, resulting in reduction of the mechanical properties in the heat-affected zones. These effects are illustrated through a brief numerical example