Effect of flexibility degree in tubular joints on continuous genetic algorithm-based optimization of offshore jacket-type platforms

The optimization of offshore jacket platforms remains a critical challenge in marine engineering, requiring a balance between structural integrity, material efficiency, and cost. This study develops a continuous genetic algorithm (CGA) framework that explicitly integrates joint flexibility and codified design criteria. Four scenarios were evaluated: rigid joints, flexible joints with MSL criteria, flexible joints with API RP 2A criteria, and fixed-brace optimization. The rigid-joint model achieved a 31% weight reduction (1,437→996 tons), while incorporating joint flexibility improved outcomes: the MSL-based flexible model achieved 34% (943 tons), and the API-based flexible model achieved the highest reduction at 35% (934 tons). These improvements were accompanied by increases in the fundamental period (1.02→1.91 s) and deflection (65.7→156.4 mm), indicating realistic stress redistribution through elastic–plastic joint behavior. In contrast, the fixed-brace model yielded only 19% savings (1,170 tons) due to restricted load paths. Convergence analysis showed stable optimization within 90–100 generations, highlighting the robustness of the CGA. Sectional results revealed that jacket legs contributed up to 42% of the optimization in constrained scenarios, while simultaneous brace–leg optimization enabled holistic weight reduction. Overall, the proposed flexibility-aware framework achieves 30–35% material savings compared with traditional rigid models, without violating API displacement and stress constraints, thereby demonstrating its value for cost-effective and safe design.