Early Age Cycling of grouted connections

The JIP has completed its first phase and at this stage we are looking for industry partners for the second phase.

Progress and Next Steps

DNV has successfully completed Phase 1 of the EAC JIP, which focused on defining key objectives, and establishing the testing scope. As a result, a comprehensive testing plan for Phase 2 has now been established. Phase 2 is set to commence in Q3 2025, with a focus on executing large-scale testing to isolate the critical factors influencing EAC. The ultimate objective of the JIP remains to establish an analytical design approach that accounts for the effects of EAC at displacements greater than 1 mm. This approach will help reduce the need for expensive and time-consuming project-specific testing for typical offshore grouted connections.

Challenge

Grouted connections are widely used in offshore wind turbine support structures, relying on high-strength grout to fill the annulus between jacket legs and piles, monopiles and transition pieces, and other structural elements. Early Age Cycling (EAC) refers to relative displacement caused by wave and current loading during grout curing.

Excessive EAC may compromise grout performance and, consequently, the integrity of the wind turbine foundation. The industry has limited research and dedicated testing on EAC, with existing evaluations largely based on small-scale tests that may not be applicable to the increasing size of offshore wind turbine structures. As a result, the industry still lacks a comprehensive understanding of the impact of EAC on grouted connections.

Objective

DNV-ST-0126 currently limits EAC effects by specifying that relative movement during the initial curing phase must not exceed 1 mm. While preventing excessive EAC displacements can lead to significant additional costs and prolonged installation times, limited testing has shown that EAC influences grouted connection capacity. The offshore wind industry is pushing for a relaxation of the 1 mm criterion, but with many different grouted connection types and numerous influencing variables—such as geometries, loads, displacements, materials, and temperatures—further research is needed to develop an informed and reliable approach.

Through this JIP, DNV aims to update EAC guidelines in DNV-ST-0126 for the most widely used grouted connections in the industry. In addition, we recognize the need to develop a standardized small-scale testing methodology to assess grout material properties and their suitability for EAC conditions.

Deliverables

Building on input from our industry partners, DNV is committed to determining the most efficient approach to improving EAC guidelines. We propose that a large-scale testing program will provide the necessary data to refine current design criteria and improve industry understanding of EAC effects. The final goal is to incorporate these insights into an analytical design framework that will enhance offshore wind project efficiency and reliability.

Industry Participation

Grouted connections remain a fundamental component of offshore wind turbine structures, and industry interest in this JIP remains strong. In Phase 1, participants from COWI, DEME, Equinor, ITW PP, IQIP, Kent, Sika, Smulders,  Parkwind, Rambøll, Ruentex  SAIPEM, Shimzu Corporation , and Ørsted all contributed, recognizing the importance of this initiative. DNV continues to welcome additional relevant parties to contribute to the discussion and help shape the next phase of research.

If you are interested in participating in this JIP, please reach out to discuss how you can be involved in shaping the future of EAC guidelines for offshore wind.