Wind-induced fatigue simulation approach for steel megastructures

Wind-induced fatigue is the phenomenon of progressive degradation and, eventually, rupture in structural elements due to continuous cyclic action of wind. The assessment of wind-induced fatigue is in general an extremely demanding and multidisciplinary activity. In fact, it requires multiple blocks which range from the simulation of wind action, simulation of structural dynamic response, climatic statistics analysis, local stress analysis and detailed fatigue calculations. For some structural cases, i.e. simple cantilever structures, light poles, traffic signals, closed formulations for assessing this loading have been proposed in recent years in literature and standards. The proposed research focuses, on the contrary, on large, complex steel structures, often called megastructures, which can be very sensitive to wind action and for which the calculation of wind-induced fatigue is not feasible using closed formulations and which is an underdeveloped subject in literature. Since megastructures are unique, simulations are necessary all along the design process, including both wind simulation and structural analysis. Up to now, wind tunnels have been the standard tool for simulating wind loading, but recent advances in High-Performance Computing (HPC), have also permitted to use numerical approaches of Computational Wind Engineering (CWE), which adopt Computational Fluid Dynamics (CFD) models. This thesis proposes a complete approach for the calculation of wind-induced fatigue in megastructures where CFD is introduced in the fatigue design process, making the process entirely numerical. Since CFD must responds to strict requirements related to accuracy, robustness and computational cost, an original development is proposed in the context of the recent and promising class of Partially Averaged Navier Stokes (PANS) models. New PANS models are developed in view of the application on transient analyses on large steel structures. These models are validated using standard benchmark cases showing improvements compared to reference models. Finally, a complete calculation of wind-induced fatigue is shown relative to the real-world application of a stadium roof thus proving the feasibility and the results of the procedure, where PANS models are envisioned as the missing link to perform an entirely numerical calculation at reasonable computational cost.