EXPERIMENTAL RESEARCH ON THE ULTIMATE AXIAL CAPACITY OF GROUTED CONNECTIONS IN TRIPOD SUPPORT STRUCTURES OF OFFSHORE WIND TURBINES

An experimental research was conducted on the ultimate capacity of axial loaded grouted tubular connections to support the design of the tripod support structure of an offshore wind turbine (OWT). Four test models were designed, including two models with shear keys and two without shear keys. The reference model with shear keys exhibited much higher axial capacity and ductility than those without shear keys. The model after fatigue cycles had almost the same ultimate capacity as the reference model, though its ductility had deteriorated. Also, four empirical equations recommended by UK, API, DNV 2013 and 2014 standards are discussed. A comparison study shows that the four standards all have some disadvantages. The forms of the API and DNV 2013 equations are not so reasonable, whereas the experimental parameters for the UK and the DNV 2014 equations are incomplete. Thus, a new formula concerning the interface shear strength of grouted connections is proposed to meet a wider range of parameters in engineering practice.