This paper presents a method for decomposition of structural products in order to provide the product designer with choices for feasible assemblies. The synthesis of assemblies is done by decomposing a complex structure obtained via structural topology optimization into an assembly of multiple structural members with simpler geometries. The aim is at providing a systematic approach to explore a large number of decompositions prior to the detailed component design phase. Initially, the structure, which is represented as a bitmap image, is transformed to a graph with equivalent topology through application of image processing algorithms. Then, the obtained graph is decomposed by a genetic algorithm into subgraphs using strength-based criteria. Results for an example structure are given to clarify and discuss the method.