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<p>A large number of offshore jacket platforms operate beyond their original design life, raising concerns about their seismic vulnerability. This study performs a fragility-based risk assessment of a 45-year-old platform in the Caspian Sea using nonlinear static pushover analysis integrated with the capacity spectrum method. Susceptibility of the structure across all four damage states (slight, moderate, severe &amp; complete) was assessed under eight horizontal loading directions (0°–315°). The analysis quantifies the influence of seismic incidence angle, future corrosion (2–4&#xa0;mm thickness loss), marine growth (1–5&#xa0;cm), and two retrofit strategies utilizing original-grade and high-strength steel. Results reveal strong directional dependence: the 135° direction governs damage initiation (slight/moderate), while the 225° direction governs collapse (severe/complete). At the site-specific Abnormal Level Earthquake demand, limiting assessment to principal axes underestimates collapse risk. Corrosion losses of 3&#xa0;mm and 4&#xa0;mm increase the vulnerability of the structure at serviceability conditions by 5% and 11%, respectively. Marine growth of 3&#xa0;cm triggers the collapse probability by nearly 290%, identifying a critical thickness threshold for maintenance. Reinstating missing bracing with original steel reduces the complete-damage exceedance probability by 66.5%, while high-strength steel (355&#xa0;MPa) reduces it by 94.6%. The findings provide quantitative criteria for inspection (alert at 3&#xa0;mm corrosion, clean at 2–3&#xa0;cm marine growth) and retrofit (use high-strength steel in high-seismic regions). This study demonstrates that directional fragility analysis, corrosion monitoring, marine growth management and targeted retrofitting are essential for safe life extension of aged jacket platforms.</p>

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Multi-scenario seismic fragility-based risk assessment of an ageing offshore jacket platform

  • 期刊论文

  • 发表日期：

    2026年7月21日

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  • P. B. Harisankar,
  • M. B. Praveen,
  • Aparna Viswanathan,
  • Chandru Pichaimuthu,
  • R. Prethiv Kumar

摘要

A large number of offshore jacket platforms operate beyond their original design life, raising concerns about their seismic vulnerability. This study performs a fragility-based risk assessment of a 45-year-old platform in the Caspian Sea using nonlinear static pushover analysis integrated with the capacity spectrum method. Susceptibility of the structure across all four damage states (slight, moderate, severe & complete) was assessed under eight horizontal loading directions (0°–315°). The analysis quantifies the influence of seismic incidence angle, future corrosion (2–4 mm thickness loss), marine growth (1–5 cm), and two retrofit strategies utilizing original-grade and high-strength steel. Results reveal strong directional dependence: the 135° direction governs damage initiation (slight/moderate), while the 225° direction governs collapse (severe/complete). At the site-specific Abnormal Level Earthquake demand, limiting assessment to principal axes underestimates collapse risk. Corrosion losses of 3 mm and 4 mm increase the vulnerability of the structure at serviceability conditions by 5% and 11%, respectively. Marine growth of 3 cm triggers the collapse probability by nearly 290%, identifying a critical thickness threshold for maintenance. Reinstating missing bracing with original steel reduces the complete-damage exceedance probability by 66.5%, while high-strength steel (355 MPa) reduces it by 94.6%. The findings provide quantitative criteria for inspection (alert at 3 mm corrosion, clean at 2–3 cm marine growth) and retrofit (use high-strength steel in high-seismic regions). This study demonstrates that directional fragility analysis, corrosion monitoring, marine growth management and targeted retrofitting are essential for safe life extension of aged jacket platforms.