On the Structural Capacity of Grouted Connections in Offshore Structures

During the last year, the offshore wind tower structure industry experienced that the design of the grouted connections between the top tower and monopile structure did not necessarily result in an acceptable safety level. A number of wind towers were reported to settle on the monopile structure and the resulting force flow in the structures was different to that intended at the design stage. A joint industry project was therefore carried out to investigate the structural capacity of these connections. It was found that the axial capacity of the grouted connections is a larger function of the diameter and surface tolerances than that accounted for in existing design standards. This paper reviews the industry practice relating to the design of grouted connections in monopile structures. The physical behaviour of the connections is explained and some of the most critical issues related to the design of large diameter grouted connections are assessed. This knowledge is also considered to be of significance for the design of grouted connections in skirt piles in jacket structures subjected to alternating loading.