<p>Single Point Anchor Reservoir (SPAR) floating offshore platforms are essential for deep-water oil and gas extraction, but their structural integrity is challenged by hydrodynamic loads and progressive structural degradation. This study develops an integrated survivability framework combining hydrodynamic load modelling, structural response analysis, and degradation mechanisms into a composite degradation index. A MATLAB-based model was developed to simulate the components. The outputs were normalized and consolidated into a composite degradation index. It quantifies structural integrity and establishes the life cycle stages. Results show that long-term structural degradation mechanisms had a greater effect on the structure than hydrodynamic loads and motions. Among them, corrosion and fatigue are identified as the major concerns. The framework is validated for the North Sea conditions using sensitivity analysis across varying sea states. Harsher sea states also increase the vulnerability to structural degradation. The higher wave heights are also revealed as the dominant driver. The gauged composite degradation index ranges from 0.92 to 0.99 over 10 to 60 years. Therefore, the SPAR structure entails repurposing due to the structural degradation and harsher environments. Accordingly, the composite degradation index serves as a decision support tool for lifecycle management and sustainable offshore engineering.</p>