Design and analysis of a wedge connection for offshore foundations

Master thesis (2017)

Authors

K.E.Y. Creusen Mechanical Engineering

Contributors

M. Veljkovic (mentor)
M.L.A. Segeren (graduation committee member)
F. Pisano (graduation committee member)
Faculty
Mechanical Engineering, Mechanical Engineering
Copyright: © 2017 Koen Creusen
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Published Date

06-11-2017

Language

English

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Faculty

Mechanical Engineering

Abstract

The offshore wind industry is developing larger turbines, often placed in deeper water. This requires larger foundations. The predominant foundation type is the steel monopile, typically consisting of two large diameter pipes, the monopile (MP) and the transition piece (TP). The Wedge Connection is a new type of connection between these components which is investigated and designed in this thesis. The core of the wedge connection is a dowel with an inclined plane on one end. A large number of these dowels is placed around the circumference in a flange fitted to the TP. Holes with an inclined plane matching the dowel are machined into an MP flange. During installation, the TP is placed on top of the MP and the holes and dowels are aligned. The dowels are displaced horizontally with a hydraulic system. The hydraulic pressure is converted into a vertical preload through the inclined plane.


In a comparison of connection concepts the strengths and weaknesses of the wedge connection with regards to other concepts are found. Two options are currently on the market, grouting and bolted flanges. Grouted connections have proven susceptible to long-term degradation, while bolted flanges have limited scalability and can be applied above the waterline only. The main benefits of the wedge connection are the option to apply it under water and the fact that no significant overlap is required. This makes the wedge connection a commercially attractive option.


The fundamental principle of the wedge connection is a vertical preload generated through an inclined plane. In a set of analytical equations the sensitivity to the wedge angle and friction coefficient is investigated. Based on these equations and the shear strength of the dowel, a preliminary design is drafted for a hypothetical foundation with 10 m diameter.


This design is modelled using ANSYS APDL. The connection is incrementally loaded up to the ultimate tensile load. A study is performed on the behaviour of the connection. The sensitivity of the connection to factors such as friction coefficient, input pressure and small geometry changes is considered.

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