In this paper we present a method for the multidisciplinary optimization of structures including qualitative expert knowledge. In addition to multi objective and discrete tasks, which are solved with a genetic algorithm, mainly expert knowledge and experience is available for certain influences in early design stages. Fuzzy Rule Based Systems (FRBS) provide a powerful tool to model such influences via qualitative human knowledge. Based on this idea, a method for building qualitative, knowledge based models has been developed at the institute and enhanced. As an example, structural components constructed from composite aluminum profiles with embedded continuous reinforcing elements have been optimized.