Long-term reliability assessment of offshore structures in complex environment

Abstract

The safety of an offshore structure is highly dependent on its resistance to the environmental loads.A realistic statistical model of the environmental parameters is essential in order to produce a safe design including a realistic estimate of the failure probability in a stochastic analysis so as to avoid unexpected failure and its associated consequences. However, the available joint distribution model can only describe the statistical dependence in a very restricted form. The use of simple probabilistic models may lead to some significant bias in the stochastic structural analysis. In this paper, the safety of an offshore structure considering multiple environmental factors is investigated. A copula-based joint probabilistic model is presented to describe several commonly used sea state parameters. A wide range of copula functions are examined in the construction of the multivariate model. The modeled sea state parameters are then utilized to characterize the load for the reliability analysis of a real jacket structure. A novel discretized subcopula approach is proposed to assess the long term performance of the jacket structure. The advantages of this innovative way of calculating the design value is demonstrated in the structural analysis. Finally, the usefulness of this new approach in more complex problems that have more environmental factors is discussed. © 2013 Taylor & Francis Group, London.