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This and the next 9 images are from:
Christine Heistermann, “Resistance of Friction Connections with Open Slotted Holes in Towers for Wind Turbines”, Ph.D dissertation, Division of Structural and Construction Engineering, Dept. of Civil, Environmental and Natural Resources Engineering, Lulea University of Technology, Sweden, 2014
ABSTRACT: The most common solutions for in-situ connections of steel tubular tower segments of onshore wind turbines are ring flange connections. These have certain drawbacks, such as e.g. costly production, long delivery time and rather low fatigue endurance. Friction connections with long open slotted holes have previously been proven to be a competitive alternative. In this work, the new type of connection is investigated in various scales: segment tests, down-scaled experiments and full-scale models. The influence of tower cross-section shape, execution tolerance (horizontal gap between the tower segments) and length of the connection on the bending resistance is thoroughly studied. In addition, buckling behaviour of the shell in the vicinity of the friction connection in towers with circular and polygonal cross-sections is analysed in order to check possible advantages of either cross-section. The influence of two types of the execution tolerances on the connection strength is investigated: inwards bent “fingers”, leading to inclined gaps, and a parallel gap created by different diameters of the tower segments. Based on validated finite element analyses recommendations for execution tolerances are proposed. A closer look is taken at the level of bolt forces under load application for the new friction connections as well as for the ring flange connection. For the former case, the influence of slotted holes on the joint resistance is checked. For both types of connections, comparison is drawn to hand calculation models used in engineering practice. Additionally, the distribution of meridional stresses in the shell in the vicinity of the connection is studied. Based on the findings from the above described investigations, recommendations for the design of friction connections with open slotted holes in steel tubular towers for onshore wind turbines are given.
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