Recently, a DNV-led joint industry project suggested a new assessment methodology for grouted connections in monopile wind turbine structures without shear keys. The reason for upgrading the industry design practices was that that the previous practices did not properly describe the physical behaviour of such connections.
The project suggested a design practice using conical shaped connections to account for large dynamic bending moments on monopiles. It did not recommend a cylindrical shaped design of grouted connections without additional support arrangements for the axial load.
It was realised that the new knowledge and methodology also would influence the design of large diameter grouted connections with shear keys. Shear keys are circumferential weld beads on the outside of the monopile and the inside of the transition piece in the grouted section. The shear keys’ purpose is to increase the sliding resistance between the grout and steel so that no settlement occurs.
However, existing design standards for such connections in sea water are based on limited test data for alternating dynamic loading. Without any design guidance on shear keys, it will be difficult for the wind industry to achieve a design using grouted connections that can be attractive from a cost point of view.
Before this solution can be recommended, new test data and design practices for shear keys should be developed and properly incorporated into design standards. DNV has therefore initiated a complementary joint industry project with the aim of updating existing knowledge of and design practices for grouted connections with shear keys. The project will especially generate test data that can be used to establish such a reliable design methodology.
A great number of key industry players have joined the project, but there are still openings for additional participants. The aim is to conclude the project early in 2012.
Due to DNV’s in-depth knowledge and role as independent partner, the company facilitates a great number of joint industry projects each year, many of them aimed specifically at developing standards. Our role since 1864 has been to assist in solving complex technical challenges faced by business and society. Developing new tools, methodologies, standards, and recommended practices together with wind industry and authorities is an important role for us.
[mappress]
Source: dnv, March 17, 2011