Design Procedure for Tubular Lattice Towers for Small Wind Turbines

Abstract

Despite having been used for a long time, tubular lattice towers with three or four legs have not been systematically analysed for use with small wind turbines. We present a design procedure based on modelling the towers as either tripods or quadrapods to allow analytic approximations to the tower stresses. Following the IEC standard for small wind turbine design, the critical load occurs at the 50-year extreme wind speed acting on a stationary turbine and tower. To avoid buckling in the downwind leg, three separate methods of estimating the critical buckling resistance are shown to give very similar results. The analytic models also allow the tower-top deflection to be simply approximated. We use an arbitrary limit on deflection as 5% of the tower height, to ensure linear, static behaviour for extreme wind loads. Two example tower designs are considered: an 18 m tower for a 5 kW turbine and a 12 m tower for a 500 W turbine.