Innovative solutions for telecommunications and transmission lattice towers
Angle sections are extensively used in lattice towers and masts for telecommunication or electricity transmission. In addition, single or built-up sections made of angles are used in a wide field of civil engineering applications including buildings, bridges or for strengthening existing structures. However, there is a lack of consistent European rules for designing members made of angle profiles and conventional steel. Recent developments have led to a wider application of large angle sections made of high strength steel, for which European design rules are simply missing. Strengthening of existing towers to mitigate local damage, sustain increased winds, or support new 5G antenna loads for communication purposes, is an issue faced in everyday practice. However, design codes cover only one specific angle member configuration, and tend to do so conservatively. The objective of the ANGELHY project, which ran from July 2017 to December 2021 was the development of design rules that exploit the carrying potential of angle sections, including large angles from high strength steel, the improvement of existing rules for built-up sections and the incorporation of innovative types of built-up sections composed of two angles with unequal sections. In addition, hybrid profiles composed of angle sections and FRP plates were investigated and relevant design rules developed. Such hybrid members provide innovative and cost effective solutions for strengthening existing lattice towers. Experimental and numerical investigations were performed at the level of cross sections, members, as well as of structural tower subassemblies to incorporate the influence of realistic connection conditions, existing eccentricities and load shedding between tower walls. Extensive case studies were examined, comprising a wireless telecommunication tower in Greece, and a power transmission power line in Germany, employing performance-based assessment of the actual system safety to incorporate uncertainties in loads, material, aging and geometry. The investigation culminated with assessing the options faced by operators and owners of aged infrastructure, considering the replacement or rehabiliation of their towers in terms of lifetime cost.