Page 76: of Offshore Engineer Magazine (May/Jun 2014)

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EPIC

New solutions for grouted connections are based on the most recent technical the temporary supports as a result of

Grouted connections have been knowledge, methodology, experience settlement in some grouted connections a challenge to the ofshore and test results.

has led to concern about fatigue cracking wind industry. The sector is

The most well-known offshore wind in the structures which would lead to turbine support structures are monopile, repair needs. During a thorough review now looking for class society gravity based, jacket, and tripod struc- of the DNV-OS-J101 standard in 2009, guidance so that the latest tures. Monopiles are the most widely we discovered that some scale effects applications for grouted used design and grouted connections are were not properly accounted for in this used to connect the transition piece to standard or in other standards for similar connections are refected in the monopile. Grouted connections have types of connections.

the latest design standards. been successfully used in the offshore oil

Joint Industry Project and gas industry on drilling and produc-

By , Claus F. Christensen tion platform jackets for the last 40 years. A Joint Industry Project (JIP) has been

DNV GL – Energy

However, the major difference for a initiated by DNV GL in order to look monopile offshore wind turbine structure further into the issue, with the aim of ind energy is a fast develop- is that, while the grouted connection solving an industry-wide challenge. ing industry, which means in jackets is mainly intended for small Conical grouted connections have been

W independent certifcation diameter piles, with large axial forces, developed and tested as an alternative bodies like DNV GL have to ensure the wind turbine monopile grouted con- design. In addition, the industry partners that widely used standards for the nection is large diameter and predomi- have been looking at grouted connections design of offshore wind turbine support nantly subjected to bending. with shear keys. structures like DNV-OS-J101 or GL-IV-2

An unintended force transfer through The joint industry project has con-

Grouted connections

A grouted connection connects the transition piece to the monopile. A transition piece is placed on top of the monopile, resting on temporary supports. During installation, the transition piece is then jacked up before grouting. After curing, the jacks are removed, leaving a gap of a few centimetres between the tempworary supports and the monopile. Settlement down to the temporary supports may result in a diferent force fow in the structures.

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