Finite Element-Based Design of Grouted Connections with Shear Keys for Offshore Wind Turbines

Abstract

Unexpected settlements in grouted connections caused concern in the offshore wind power industry. A grouted connection connects the transition piece of the tubular turbine tower to the monopile foundation by an annulus filled with high-strength grout. On several wind turbines, the transition piece has moved several centimetres downwards. Since the discovery of this serious problem, the generally applied codes for the design of grouted connections are under revision, and alternative solutions are investigated. Shear keys on the steel surfaces increase the capacity of the connection significantly. The paper discusses various approaches to finite element modelling of grouted connections with shear keys. For the design and the corresponding certifying process, advanced three-dimensional finite element models have been developed by the authors. The models consider the complex interface behaviour between steel and grout, the nonlinear material behaviour, and the detailed geometry of the shear keys. The results of the analysis are compared with laboratory tests on small-scale grouted connections and show good agreement. Furthermore, a comparison is made with recently published design guides.