The use of bolted flange connections in the offshore wind industry has steeply risen in the last few years. This trend is because of failings observed in other modes of joints such as grouted joints, coupled with enormous economic losses associated with such failures. As many aspects of bolted flange connections for the offshore wind industry are yet to be understood in full, the current study undertakes a comprehensive review of the lessons learned about bolted connections from a range of industries such as nuclear, aerospace, and onshore wind for application in offshore wind industry. Subsequently, the collected information could be used to effectively address and investigate ways to improve bolted flange connections in the offshore wind industry. As monopiles constitute an overwhelming majority of foundation types used in the current offshore wind market, this work focusses on large diameter flanges in the primary load path of a wind turbine foundation, such as those typically found at the base of turbine towers, or at monopile to transition piece connections. Finally, a summary of issues associated with flanges as well as bolted connections is provided, and insights are recommended on the direction to be followed to address these concerns.

Cracks are commonly observed at the hot spot stress location of tubular joints and it can be due to fatigue, accidental damage or corrosion. As a consequence, the plastic collapse load (P_c) of the tubular joints is reduced, and hence it is necessary to produce design guidance which can safely be used to estimate the static residual strength of cracked tubular structures in practice. This paper proposes a new expression for determining the reduction factor (F_AR) of cracked square hollow section (SHS) K-joints. A completely new and robust finite element mesh generator which is validated using the full scale experimental test results is used for the parametric study to propose the new F_AR expressions for cracked SHS K-joints. The crack area and the brace to chord width ratio (β) are shown to have the most profound effect on the P_c load of cracked SHS K-joints. For a given value of crack area, the variation of the F_AR values is up to 3.6% for different values of β. Furthermore, the F_AR values calculated using the existing equation given in the latest BS 7910:2013 + A1:2015 for circular hollow section (CHS) joints are revealed to be conservative up to 23.5%.