The Influence of Soil-Structure-Interaction on the Fatigue Analysis in the Foundation Design of Onshore Wind Turbines

Abstract

The growth of wind turbine size entails the necessity of research and advances in foundation design. To increase the efficiency of alternative energy resources wind turbines also need to be designed for longer life-spans. Because of this it is inevitable to gain deeper understandings of the continuous stress in the foundation and the influence of the soil-structure interaction (SSI) effects on the dynamic response of wind turbines, especially when grounded on soft or inhomogenous soil. Current standards emphasise the need of the SSI analysis during the whole design phase of the turbine, the tower and the foundation as well as the need of detailed fatigue design.In this study the foundation design of a wind turbine is carried out regarding to the current standards, also including SSI via state of the art methods. Major influences on the wind turbine foundation design are the overturning moment, the bending of the foundation and the connection of the tower to the foundation. Nevertheless, the special focus of this study lies on the detailed fatigue design of the concrete in the foundation using the rainflow algorithm. However, fatigue design can lead to the necessity of stronger concrete and a higher rate of reinforcement steel. The main objectives of this study are: (1) to determine the influence of state of the art SSI in the foundation design on the fatigue load design via the different soil parameters and the arising foundation geometry and material properties. (2) to show how the fatigue design differs while considering standard SSI or more detailed calculation methods.