EUROSTEEL 2017, September 13–15, 2017, Copenhagen, Denmark Numerical investigation of preloaded gusset plate connections between polygonal built-up members Slobodanka Jovašević* ,a , Carlos Rebelo a , Marko Pavlović b , Milan Veljković b a ISISE, Department of Civil Engineering, University of Coimbra, P-3004 516, Coimbra, Portugal sjovasevic@uc.pt, crebelo@dec.uc.pt b Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, Netherlands M.Pavlovic@tudelft.nl, m.veljkovic@tudelft.nl ABSTRACT In the last decades, the demand for renewable energies, including wind energy, is increasing. With this increase, more powerful wind energy converters are needed, which require higher supporting structure that allow to reach zones of higher wind speed with less turbulences. The most commonly used type of the tower is steel tubular tower. Height of these towers is limited by manufacturing and transportation logistics. The solution to overcome these issues might be construction of lattice towers. The major disadvantage of lattice towers is large number of the installed bolts. Therefore, the steel hybrid tower that combines the advantages of steel lattice (lower part) and tubular tower (upper part) was proposed in SHOWTIME project. The sections used in lattice portion of the tower are built-up polygonal sections composed of cold-formed pieces connected together with preloaded bolts. The goal with using built-up polygonal cross-section is to minimize number of connections by increasing the member length. The focus in this paper is numerical investigation of preloaded gusset plate connections between these types of members. The finite element software ABAQUS has been used in the study. The aim of the investigation is to determine the failure modes of the elements and connections, as well as stiffness and ultimate resistance of the connections. Keywords: gusset plate connections, polygonal built up sections, lattice wind towers. 1 INTRODUCTION The European Union target to cover at least 27% of total energy consumption from renewable sources until 2030 has increased the demand for wind energy [1]. This increase is leading to construction of more powerful wind energy converters. Therefore, higher towers are required, what results in transportation, assembly, erection and maintenance costs increase [2, 3]. For the heights up to 100m the most commonly used is steel tubular tower. For the higher heights one of possible solutions is steel hybrid tower (Fig 2). This type of the tower uses for upper portion tubular steel tower with diameters within public load transportation limits. The extension of the height is achieved with lower portion made as lattice structure [4]. The main advantage of using the lattice portion is to facilitate installation of the upper tubular portion and the turbine, therefore avoiding the need for very high cranes. New types of bolted and welded cross-section were proposed for the lattice portion of the tower. The cross-sections are composed of cold formed pieces connected together with preloaded bolts creating polygonal cross-sections. For the pylon three pieces are bolted or two pieces are welded together forming nonagonal, while for the brace two pieces are bolted together forming hexagonal cross-section (Fig 1). Polygonal built-up cross-section are to be used instead of CHS in order to use advantages of polygonal over circular sections [5], as well as to improve fatigue life of the connections and members considering that the fatigue behaviour of preloaded high strength bolted joints under shear or friction loads can bear higher fatigue loads then welded joints [6]. 292 https://doi.org/10.1002/cepa.60 wileyonlinelibrary.com/journal/cepa © Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin · ce/papers 1 (2017), No. 2 & 3