Introducing the C1 Wedge Connection

Abstract

Increasing loads on the connections of tubular towers that support wind turbines are making the traditional bolted L-flange more challenging to design, while the large mass of components and tools make installation challenging from a safety perspective. The C1 Wedge Connection is a symmetrical connection between tubular sections. The connection consists of a cylindrical lower flange and a fork-shaped upper flange that slides over the lower flange. Both flanges have radial elongated holes distributed along the perimeter allowing the C1 fasteners to pull the two flanges together. The fastener assembly of the C1 Wedge Connection uses a small, horizontally placed bolt to pull two wedges together. The wedges transform and magnify the horizontal bolt force into a larger preload between the flanges by pulling them together. The orientation of the bolt in the fastener prevents significant load fluctuations under external loading. As a result, unlike a bolted L-flange, the C1 Wedge Connection is less susceptible to preload loss, thereby eliminating the need for regular maintenance and inspection. The scalability of the C1 Wedge Connection makes it suitable for larger loads. These larger loads are expected with increasing size of wind turbines and when connections are used in more demanding locations such as hurricane and seismic conditions or where connections are subjected to high dynamic loads caused by extreme wave conditions or on floating foundations.

Numerical Fatigue Strength curve for the C1 Wedge Connection

“…The C1 Wedge Connection, shown in Figure 1, is a symmetrical connection developed for assembling wind turbines tubular towers [3]. The connection consists of a cylindrical lower flange and a fork-shaped upper flange that slides over the lower flange.…”

“…In this study the version used in the experimental test presented in ref. [3] is adopted which will be used for comparison. Only one segment from the full ring is considered for the sake of simplicity, as shown in Fig.…”

“…This is due to the large bolt size required to satisfy the loading demands. In some designs, the bolt size can be even larger than M72 which causes HSE (Health, Safety and Environment) issues [3]. Lochan et al [4] highlighted the lack of experimental evidences and the inadequacy of current design codes to assess the fatigue performance of large scale bolts (i.e.…”

“…According to Shakeri et al [5], an important number of wind turbine failures in Denmark are associated with fatigue failure of bolts. The C1 Connection [3] is an innovative solution for assembling wind turbine support structure segments that overcome the issues observed in the traditional L-flange connection as it requires relatively smaller bolts, can achieve high ultimate strength, and more importantly an increased fatigue life.…”