Structural behaviour and design of grouted connections cast with neat seawater mixed OPC

Seawater mixed neat ordinary Portland cement (OPC) has been used to connect tubular members of offshore structures since the 1940s in the Oil and Gas industry. More recently seawater mixed neat OPC has been used to connect the foundation piles of offshore wind turbine jacket structures, some of these structures are now since over 10 years in operation. The design of these connections was carried out mostly using design guidance stipulated in ISO 19902 or DNVGL Certification Guidelines. Despite the vast amount of documented background data substantiating these codes, it was to date not possible to readily carry out or certify design in accordance with the Eurocode design family, although constituent materials OPC CEM I and seawater as a mixing water are defined in EN 206 and EN 1008. The use of neat seawater cement grout, i.e. without any aggregates, is not covered in EN 1992 as a primary load carrying material. The aim of this work is to give comprehensive guidance for a Eurocode compliant design of concentric subsea connections grouted with seawater mixed neat OPC and subject to static and cyclical axial load with coexisting bending. All critical elements of the semi-probabilistic design framework, consisting of material models of the constituent and mixed materials, durability considerations, parameters affecting the performance of the assembled connection and the structural stress model, are critically reviewed. Guidance is based on a statistical analysis of over 500 material property tests carried out to investigate all main material parameters required for design and execution. In this work the results are compared to relevant parameter descriptions of EN 206 and EN 1992 and are integrated into a guidance to use of these formulae based on statistical analysis. Durability aspects such as sulphate and chloride resistance are examined under consideration of the high heat of hydration. The validation of ISO 19902 design rules for large annuli connection is reviewed and fatigue guidance is compared to recent historic data points from over 200 static and cyclic large- and full-scale assembly tests, including a limited number of submerged cyclical tests. A three-dimensional stress model, based on Lame’s equation is derived akin to interference fit assemblies. The model is integrated into EN1992 verification rules, to assess design resistance capacity. Finally, the Eurocode compliant simplified design approach is compared in a parameter study with the substantiated ISO 19902 design formulae to test and validate the approach. The reliability levels related to the proposed design formulae are statistically validated following the guidance of DIN EN 1990 Appendix D for design assisted by testing using available data base of more than 200 large-scale tests.