Development of Design Rules for the Use of New High-Strength Steels for Lattice Towers

Lattice towers have been in the past designed in S235 steel grade, which has been then substituted by S275 and S355 steel grades. Although the high strength steel S460 has been officially defined within EN10025-2 since 2019, its use on the market is remaining rather limited due to lack of design recommendations in the normative documents.
The present study conducted by Elia and its partners being University of Liège and ArcelorMittal company aims to provide design guidelines for the use of the S460 high strength steel in lattice towers. This is an essential first step as the current design codes do not cover this grade of steel.
The main motivations of Elia to conduct this research are the following ones:
o The current increase in energy transport is asking for uprating conductors to bigger sections which results in the request for higher bearing capacity of towers. The use of a higher steel grade could meet this demand without requesting the redesign of existing towers, which means a gain in time and human resources.
o Public acceptance is becoming a major point of reflexion, higher grade of steel would allow slender structures, lower weight and CO2 footprint.
o Elia is presently developing a 240m height transmission tower where significant compression loads (i.e. about 15 MN or 1.500ton) are met in the main legs of the tower. A butterfly leg made of S460 could potentially be able to support these loads, allowing to avoid the use of box-section designs; the former structural solution leads to a lighter structure that is less complicated to design and obviously more conventional and easy to produce, compared to box-sections.
Therefore, this paper presents the first outcomes of the conducted research, the associated experimental test results and the first application of this new grade of steel made by Elia.