A probabilistic approach to investigate uncertainty propagation in wind engineering problems

Wind engineering problems are characterized by the significant uncertainty affecting both the acting loads and the structural characteristics. A relevant contribution is given by the uncertainty of the parameters that are usually taken into account to describe both the aerodynamic and/or aeroelastic characteristics of the structure and the wind-structure interaction. Moreover, due to the stochastic nature of wind, significant uncertainty arises from the characterization of the site specific Aeolian hazard. Recently a new engineering discipline with the goal of applying Performance-Based Design (PBD) concepts to wind engineering has been proposed: the so-called Performance-Based Wind Engineering (PBWE). In the framework of PBWE, design has to be carried out always in probabilistic terms; therefore suitable techniques are required to govern the propagation of uncertainty. In the paper, an original classification of the sources of uncertainty in wind engineering is proposed. This classification suggests some assumptions regarding the uncertainty propagation; the formal analytical representation of the propagation is expressed in terms of conditional probabilities. The result of the procedure is a set of probabilistic relations between the stochastic parameters characterizing the input and the structural response. The procedure has been applied to a case study: the design of an offshore wind turbine having a jacket support structure. The probabilistic response of the structure has been investigated and the relative importance of the various sources of uncertainty assessed. The structural analyses have been carried out in frequency domain and the probabilistic characterization of the response parameters has been derived by Monte Carlo simulation. Sensitivity analyses allow to assess the robustness of the probabilistic approach.