The wind speed profile over the height of a structure in high intensity wind (HIW) events, such as downbursts, differs from that associated with traditional atmospheric boundary layer (ABL) winds. Current design codes for lattice transmission towers contain only limited advice on HIW, and structural design is often carried out using a procedure developed for ABL winds. Furthermore, the load effects due to the relative orientation of a tower to HIW event are not well understood. The present study assesses the yield and maximum capacity of a self-supported transmission tower under downburst outflow winds, including the effects of material and geometric nonlinear behaviour. The force-deformation relationship, also known as a capacity curve, for the tower is obtained for a range of wind directions and represents the relationship between the base shear of the tower and the displacement of the tip. The capacity curve of a tower is a convenient way to assess a tower design under HIW, as the definition of a reference wind speed between downburst events is challenging due to number of parameters affecting the downburst wind profile. Capacity curves based on two downburst scenarios are obtained for oblique wind directions, and their differences are shown to be related to the shape of the loading profile, and therefore the size of the downburst. It is shown that the lowest yield capacity tends to occur at a wind direction of approximately 45°, and that the tower has a greater capacity when the loading is concentrated at mid-height as opposed to the upper portion.
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