Investigation of the ergodicity assumption for sea states in the reliability assessment of offshore structures.

Various schemes for the computation of structural reliability in the presence of ergodic wave load processes, ergodic sea state sequences and simple (non-ergodic) random variables such as strength parameters or statistical uncertainties are investigated for both non-deteriorating and deteriorating structural properties. It is assumed that at least conditional outcrossing rates can be computed. It is found that rigorous formulations can require substantial numerical effort even in the context of FORM/SORM computation schemes as they require nested integration. However, for high reliability and not too large variabilities of the non- ergodic variables simpler computation schemes can be used. In the non-deteriorating case, use of the ergodic theorem can be made. In the deteriorating case Jensen's inequality can be applied to arrive at simple and appropriate computational schemes. (A)