Future generations of civil aircrafts and unconventional unmanned configurations demand for innovative structural concepts to obtain the structural performance, and thus reduce the structural weight. For instance, one of the method to improve structural component is the material coupling used to alter static and dynamic aeroelastic stabilities. It is therefore useful to use an accurate and computationally efficient beam model during the preliminary design phase. In the present work, a numerical validation of equivalent homogeneous orthotropic material procedure, described in  and , is performed by the application of structural topology optimization technique  on a box beam made of isotropic material. The overall equivalent bending, torsional and coupled stiffness is derived by means of homogenization of the shell skin and of the stiffener plate stiffness. The optimum theoretical conditions of bending-torsion coupling was obtained when stiffeners were oriented at about 27°. The numerical validation is performed imposing the maximizing of the global compliance fulfilling topology optimization constraints as tip’s static rotation, global symmetry and manufactory constraints. Good agreement has been found between the theoretical simplified beam model and numerical analysis. The maximum compliance obtainable was found when the stiffeners are positioned to an angle comprised between 25° and 30° as shown in figure 1 confirming the validity of the simplified beam model.