Behaviour of pretensioned bolts in friction connections : towards the use of higher strength steels in wind towers

Abstract: During recent years wind energy has established as an alternative to commonenergy sources. To advance its competitiveness, the costs for the constructionof a wind tower have to be reduced. One possible option is the use of frictiongrip joints instead of flange connections to join various tower segments in atubular steel tower. Additionally, the time necessary for installation andmaintenance of the bolts in these connections can be decreased, not only forimplementation in tubular towers but also in lattice towers.Four different bolt types have been investigated with respect to the ease ofinstallation and maintenance on the one hand and structural applicability on theother hand. The latter one is mainly defined by the behaviour of the pretensionforce in the bolts. Various influences on the reduction of clamping force areexperimentally checked, such as the type and thickness of coating, thethickness of the clamping package and external loading.The slip factor, which plays an important role in friction connections, isexperimentally achieved in a test on a double shear lap joint. The experiment isthoroughly examined by a finite element analysis, which models the interactionbetween bolts and plates.In various numerical analyses the influence of steel grade and possibleassembling tolerances on the resistance of a friction joint is investigated bothfor single and double shear lap joints.Shortages of EN 1993 parts 1-8 and 1-12 for the use of slip critical joints areidentified.