Abstract
Tensile stresses in the tension legs attached to a large floating island are evaluated for wind waves and seaquakes by a wet mode superposition approach and random vibration theory. The conditional failure probabilities of tension legs are calculated by solving a first passage problem for different load intensities of each loading. Then, unconditional failure probabilities of both loadings are separately calculated by multiplying the conditional failure probabilities by the corresponding occurrence rates and integrating them with respect to all possible load intensities. The minimum required stiffness of tension legs is determined in such a way that the summation of lifetime failure probabilities of both loadings becomes less than a target failure probability. Numerical examples are presented to illustrate how to determine the minimum required stiffness of tension legs at different offshore sites.
