The design of astronomical instrument is growing in dimension and complexity, following the new requirements imposed by ELT class telescopes. The availability of new structural material like composite ones is asking for more robust and reliable designing numerical tools. This paper wants to show a possible integrated design framework. The procedure starts from the developing of a raw structure consisting in an assembly of plates and beams directly from the optical design. The basic Finite Element Model is then prepared joining together plate and beam elements for the structure and mass and semi-rigid element for the the opto-mechanical subsystems. The technique developed is based onto Matlab® commands and run the FEA, extrapolate the optical displacements, implement them into the optical design and evaluates the image quality in terms of displacement and spot size. Thanks to a simplified procedure the routine is able to derive the full field of displacements from a reduced sequence of three different load sets. The automatic optimization routine modifies the properties of plates and beams considering also different materials and, in case of composites different lamination sequences. The algorithm is oriented to find the best compromise in terms of overall weights w.r.t. eigen-frequencies, image stability and quality.