AbstractA new finite element method modeling technique was developed for the stress analysis of the U-shaped bellows, which is more convenient for the stress analysis of such a complicated structure as the JT-60 vacuum vessel. In the present modeling method, the bellows are replaced by an orthotropic plate having the same rigidity as the bellows. The real stress of the bellows is obtained by transformation equations, which express a physical correspondence between the membrane stresses and bending moments of the orthotropic plate and those of the bellows. The applicability of the present modeling technique was verified using four kinds of test models. The experimental results agreed well with the computed ones, and the present stress analysis method of the U-shaped bellows was found to be sufficiently applicable to the stress analysis of the JT-60 vacuum vessel.