Behaviour of Steel Lattice Tower with Partially Preloaded Bolted Splices

In steel lattice towers bearing type bolted connections, category A according to EN 1993-1-8, are most often used. Clearance between the bolt and the hole diameters may cause slip of the joined elements, which can influence the structural behaviour of the tower. Usually, such connections are considered as loosely bolted, and slip can occur immediately after loading the joint with a small amount of longitudinal force. The paper presents the structural response of a steel tower with a height of 40.5 m, located in Poland, in which Category A bolted connections were taken into account, but with the possibility of the occurrence of friction forces in contact members, resulting from the tightening of the bolts by the hand or portable cordless impact wrench to a certain level of preload. It is shown how bolt tightening causing partial preload of bolts, being only a fraction of bolt preload applied in the case of Category B or C joints, changes the structural response of the whole tower, with particular emphasis on its deflection in serviceability limit state. Analysis shows, that tightening of the bolts to approximately 60% of the full preload radically changes the structural response of the whole tower compared to loosely tightened connections.