Present paper proposes a structural optimization method for truss and frame structures having some uncertain factors in its constitutive materials, configurations or design loads by using fuzzy theory as well as genetic algorithm techniques. Genetic algorithm has been already recognized as a strong and a useful tool for optimization problems with discrete variables and has been applied for topology optimization problems of trusses and frames. On the other hand, uncertainties which exist in structural problems such as those of the design loads, of the structural configurations and of the constitutive materials should be dealt with from the view point of the practical structural design. The probability statistics theory has been considered as the only technique for reliability analysis that can treat the uncertainty in structures. Probability theory can be used, when there is sufficient random data to define the probability density function. However, in actual structure design, such cases can be said to be very rare. Furthermore, although various factors (human error, etc.) must also be taken into consideration in order to consider the safety of structures, they cannot be defined within a framework of the probability theory. In this paper, such factors are included by use of the fuzzy theory and the topology optimization problem of frame structures, which have uncertainties in their materials or configrations, is shown to be rationally solved.
