Material optimisation use in steel lattice wind turbine towers

Since sustainable energy production has become essential in order to confine the Greenhouse effect consequences, the number of wind farm installation will continue to rise. In addition, since the tower of on-shore wind power generators is about one third of the initial construction cost, there is additional investigation needed to optimize the tower configuration, aiming in eliminating the initial cost and the material used. To this end, and towards taking advantage of the higher energy potential in greater heights, the wind converters’ tower concept needs to be configured to be lighter and taller. Getting inspiration from telecommunication masts that are constructed as lattice towers and taking into account certain transportation restrictions of classic tubular wind tower subparts, the solution of lattice wind turbine towers is implemented aiming to achieve greater tower heights. The structural behavior of telecommunication masts has been investigated in the work of Tsitlakidou et al. and Efthymiou et al. , mainly concentrating on towers consisting of standard L shaped cross-sections fabricated in the factory and mounted on site. For wind converters, the scale of the lattice structure capable of supporting the weight and function of the nacelle is way outside the conventional industrial steel profiles. The lattice tower proposed to accommodate the wind converter has a form of a truncated cone with a square cross-section. This type of tower is a statically determinate system, composed of a certain number of discrete structural sub-systems, each with a certain function and applicability. These sub-systems are: the legs, the bracing trusses on the faces, horizontal braces and secondary bracings arranged in the plane of the face bracing trusses and outside (hip braces). All the aforementioned structural sub-systems serve for a particular role in the load transfer mechanism of the lattice tower and since the whole structure is considered a structurally determinate system, the axial stresses of the members can be determined by closed form expressions. The present paper addresses the stability performance of a lattice steel wind turbine tower, examining alternative solutions of bracings. More specifically the tower has the same height of an equivalent tubular one and bears the same loading. An algorithm has been elaborated in Mathematica software that uses an iterative procedure to design the tower members, the need of secondary and hip bracing and evaluates the total material used. The iterative procedures solves the material optimization problem and provides valuable feedback on the effect of secondary bracings on the economy of the material and the tower’s structural robustness.