en Optimal design Optimal design پژوهشي Research In this paper, for topology optimization of double layer grids, an efficient optimization method is presented by combination of Imperialist Competitive Algorithm (ICA) and Gravitational Search Algorithm (GSA) which is called ICA-GSA method. The present hybrid method is based on ICA but the moving of countries toward their relevant imperialist is done using the law of gravity of GSA. In topology optimization process, the weight of the structure is minimized subjected to displacements of joints, internal stress and slenderness ratio of members constraints. Through numerical example, topology optimization of a typical large-scale double layer grid is obtained by ICA, GSA and ICA-GSA methods. The numerical results indicate that the proposed algorithm, ICA-GSA, executes better than ICA, GSA and the other methods presented in the literatures for topology optimization of largescale skeletal structures. double layer grids, topology optimization, gravitational search algorithm, imperialist competitive algorithm 353 374 http://ijoce.iust.ac.ir/browse.php?a_code=A-10-66-72&slc_lang=en&sid=1 M. Mashayekhi 18003194753284600846 18003194753284600846 No E. Salajegheh 18003194753284600847 18003194753284600847 Yes M. Dehghani 18003194753284600848 18003194753284600848 No