Multicriteria fuzzy optimization of structural systems

This paper proposes an e¦cient, systematic and generalized multicriteria fuzzy optimum design method for the structural systems, using the suboptimization concept, introduction of measure membership functions and fuzzy decision-making techniques. Each objective function is suboptimized Þrst for all discrete sets of common design variables and design parameters. In order to make the relative evaluation of suboptimized data of objective functions rationally and systematically, and involve the fuzziness or tolerance in the decision-making process and design emphases, the measure membership functions are introduced for all objective functions. The membership functions of the suboptimized objective functions are determined systematically using the corresponding measure membership functions as datum. A hybrid decision-making process is developed combining the weighted operator method, comparison processes of maximum membership values and backward interpolation processes for the determination of the global optimum solution. The weighted operator method can also involve the relative emphases of each objective function simply. A design example of a practical prestressed concrete bridge system, in which the total expected cost after an earthquake and the aesthetics of the bridge system are the primary objectives, clariÞes the applicability to any convex and non-convex design problems, rationality, systematic design process and e¦ciency of the proposed design method