Fragility analysis of steel and concrete wind turbine towers

The tower is an essential component of a wind turbine assembly with its cost amounting to approximately 30% of the overall turbine costs for onshore installations. This paper investigates the relative performance of steel and concrete tower solutions for a selection of heights and wind speeds by means of a flapwise numerical model. For each case, elements of a baseline 5 MW wind turbine are used to model the components supported by the tower. The Lagrangian approach is used to establish the equations of motion of the dynamic system, allowing for the coupling of the tower and the system of blades. The analysis is performed for a range of typical tower heights from 88 to 120 m. Comparison of the relative performance of the two tower solutions is presented using fragility curves. This illustrates the probabilistic characteristics of limit state exceedance as a function of wind loading.