In this paper, the process of optimum design of structures is developed in which design parameters with a fuzzy nature are considered. The fuzzy optimum problem is transformed into an ordinary unconstrained optimum problem by expressing the objective function in the form of fuzzy expected cost. The proposed method is much simpler than the conventional fuzzy optimum method and appears to be able ... [Show full abstract] to deal with the uncertainty with the minimum of complexity. The proposed method can be shown to possess the following advantages: 1.(1) no predetermined mapping function is needed2.(2) consistency between objective and constrained functions is obtained3.(3) the computational process is simplified4.(4) the optimum level design is obtained. Illustrative numerical examples have been presented and the above mentioned advantages have been proved. Moreover, a comparison between various cases for both system failure cost and fuzziness of design parameters is performed.