Steel Towers for Wind Turbines

Tese de doutoramento em Construção Metálica e Mista, apresentada ao Departamento de Engenharia Civil da Faculdade de Ciências e Tecnologia da Universidade de Coimbra ; In the last few years it was registered an increase in the exploitation of renewable energies, namely wind energy, due to the increasing concern about the environmental problems related with the global warming. The forecast of the official entities is to increase the exploitation of the wind energy of around 61% in the European Union territory until 2020, with the implementation of newer structures for wind turbines. The same trend is followed worldwide with an increase of around 47% in the cumulative wind power installations in the same period. The technological development of wind energy converters (WEC) make it possible to increase the power and consequently the rotor diameter of horizontal axis wind turbines (HAWT). The main hypothesis to carry out this improvement is based on the premises of the increase in height of the wind towers to allow the exploitation of stronger and more stable wind shear profiles therefore increasing the power production and the efficiency of the wind turbine. Therefore higher towers and more efficient and cost effective foundations are required for the new generation of wind energy exploitation. The increase in the height of the currently used tubular steel towers is possible given that the main problem that arises with the increase of diameter of the tube can be solved. Indeed, the transportation requirements with a maximum diameter of about 4.5 meters possible in public roads remains a major problem, allied with increase of fatigue loads in the flange connections and increase in the foundations dimensions. The work presented in this thesis has been developed in the scope of two European projects (HISTWIN and HISTWIN2) where the issues related to new type of connections in tubular towers, allowing for modularization and easier transportation, and to the improvement of foundations were studied. The behaviour of the ...