Overview
EN ISO 19905-1:2023/A1:2025 (CEN adoption) is an amendment to ISO 19905-1:2023 - the site-specific assessment standard for jack-up mobile offshore units elevated at a site. This Amendment 1 issues targeted corrections to the strength assessment of tubular members, updates Table B‑2 (partial material factor), and replaces the simplified free‑field liquefaction assessment calculation method. The changes were approved by CEN in 2025 and apply across CEN member national standards.
Key Topics
- Scope: Site‑specific assessment procedures for jack‑ups (elevated at a site) used in oil & gas and lower‑carbon energy activities.
- Tubular member strength corrections: Revised formulae and checks for combined axial tension/compression, bending, shear and torsion (Annex A.12.5.3.3). The amendment corrects representative strengths and reduction factors used to compute tensile, local buckling and bending capacities.
- Partial material factor update: Table B‑2 first row replaced to set γ_m (partial material factor for calculated foundation capacities) = 1.25.
- Simplified free‑field liquefaction method: Clause E.5 replaced with a clarified simplified method that:
- Computes the normalized cyclic resistance ratio (CRR*, λ_CR R) from either shear wave velocity (Vs) or CPT cone resistance,
- Computes the normalized cyclic stress ratio (CSR*, λ_CSR) for the site,
- Indicates liquefaction where λ_CSR exceeds λ_CR R.
- Includes explicit formulae (E.5‑1, E.5‑2) based on published correlations (e.g., Kayen et al. 2013) and guidance on probabilistic treatment (probability of liquefaction, PL).
- Editorial and numerical corrections: Multiple formula replacements and clarifications to ensure consistent implementation.
Applications
This amendment is directly applicable to:
- Offshore structural and geotechnical engineers performing site‑specific assessments and design verification of jack‑ups.
- Design offices and engineering consultancies preparing foundation capacity calculations, member strength checks and liquefaction assessments.
- Classification societies, regulators and asset owners requiring compliance with the EN/ISO benchmark for jack‑up installation and operation.
- Contractors and installation teams needing validated assessment outputs for safe jacking/operation decisions.
Practical uses include jack‑up pre‑installation assessments, design checks for tubular leg strength under combined loads, foundation capacity verification and simplified earthquake‑induced liquefaction screening using Vs or CPT data.
Related Standards
- ISO 19905 series (site‑specific assessment of mobile offshore units)
- ISO/TC 67 and CEN/TC 12 guidance documents for offshore structures and geotechnical assessment
Keywords: EN ISO 19905-1:2023/A1:2025, jack-up, site-specific assessment, mobile offshore units, liquefaction assessment, tubular member strength, partial material factor, CPT, shear wave velocity, offshore engineering.
