Tension–Compression Fatigue Behaviour of Jacket Grouted Connections with Different Grout Strengths

Grouted connections are widely used in offshore jacket structures and are often subjected to eccentric compression and tension–compression cyclic loading arising from installation deviations and environmental actions. This study presents a comparative investigation of the fatigue behaviour of jacket grouted connections fabricated with ultra-high-strength and normal-strength grout. Preliminary static tests were conducted to evaluate the connection capacities and to determine the corresponding fatigue load levels; these were then followed by tension–compression fatigue tests under identical external cyclic loading. The ultra-high-strength grout specimen maintained a longer stable response, whereas the normal-strength grout specimen exhibited grout crushing, interface slip, and accelerated degradation at an earlier stage. The normal-strength grout connection also showed a lower static capacity and, consequently, experienced a higher normalised fatigue load level under the same external load, which was accompanied by a substantially shorter fatigue life. Comparisons with the provisions of ISO, NORSOK, and DNV revealed that the measured fatigue lives of both specimens exceeded the corresponding code-based predictions. These findings indicate that the fatigue behaviour of grouted connections under a given external load is closely related to the grout properties, the connection capacity, and the resulting relative load level.