One of the research ways carried out in the ARIAM-LAREA laboratory aims at giving to architects computing tools for early evaluation of structures. A particular approach uses dimensional analysis and similitude properties in order to define parameter variation laws. Such laws are illustrated by analytical cases using the theory of strength of materials. For complex structures, a heuristic is proposed to give indications of parameter variation influence on mechanical behaviour. Some applications are presented for early determination of structural size and limit values, using computations by finite element method.