Early age movement in offshore structures with various bearing conditions

Abstract

Grouted connections (GCs) consist of two infiltrating steel tubes of different diameters and a grout material bonding the two steel tubes together. Predominantly, the GCs are used to connect the foundation piles with the jacket support structure. Additionally, it can be applied for monopile substructures. A challenging and scientifically still marginally analysed detail of grouted connections is the influence of early age movement (EAM), also known as early age cycling (EAC) on the final load bearing behaviour of the connection. After grouting and until the end of the curing of the material, the offshore structure is partially supported by fluid grout material for several hours. During this time waves and current affect the soft connections. This leads to relative movement during the curing of GCs, which is known as EAM. Previous investigations showed grout material damage due to vertical EAM. These results form the basis of the current offshore guideline limits. According to DNVGL-OS-J101 from 2014, it must be ensured that during the curing process the vertical EAM does not exceed 1 mm. Since 2016 the limit value also applies for the lateral EAM according to DNVGL. However, the influence of lateral EAM on the load bearing behaviour is barely experimentally nor numerically investigated. Thus, the authors are involved in a comprehensive research project (GREAM) addressing this topic. This paper focusses on Finite Element Analysis of different support structures under varying boundary conditions and sea states to analyse the amplitude of lateral EAM of grouted connections.