Design of lattice towers from hot-rolled equal leg steel angles

Angles profiles have been used since the very beginning of steel construction due to their easy transportation and on-site erection. However, they exhibit specific features that clearly distinguish them from other types of common sections, what inevitably leads to the need for the development of specific design provisions. In a first step, existing European specifications on hot-rolled equal angle sections were critically reviewed and then, in a second step, extensive experimental, analytical and numerical studies have been conducted to propose a complete and duly validated set of design rules covering all aspects of design for angles. These rules include cross section classification, cross section resistance for all types of loading as well as rules for member design to individual and combined internal normal forces and moments. All the proposed rules are written in Eurocode 3 format to allow a direct possible inclusion in forthcoming drafts.
Furthermore, angle profiles are extensively used in lattice towers and masts for telecommunication purposes or electric power transmission. Such types of towers are mainly designed according to EN 1993-3-1 and EN 50341-1, based on a first-order linear elastic structural analysis of a truss structure. An assessment of the current design approach is performed, where the tower has been simulated with a full non-linear finite element software, considering relevant imperfections as well as geometrical and material non-linearities. The importance of the second order effects in the analysis is underlined while the existence of an instability mode not properly covered directly by the norms, and usually therefore not checked, is highlighted. Two analytical models for the prediction of the critical load of the new buckling mode are proposed and validated numerically. Both proposed models are rather easy to apply and may fill the gap in the existing design recommendations for lattice towers.