UNE-EN ISO 19901-2:2022

This document contains requirements for defining the seismic design procedures and criteria for offshorestructures; guidance on the requirements is included in Annex A. The requirements focus on fixed steel offshorestructures and fixed concrete offshore structures. The effects of seismic events on floating structures and partiallybuoyant structures are briefly discussed. The site-specific assessment of jack-ups in elevated condition is onlycovered in this document to the extent that the requirements are applicable.Only earthquake-induced ground motions are addressed in detail. Other geologically induced hazards such asliquefaction, slope instability, faults, tsunamis, mud volcanoes and shock waves are mentioned and brieflydiscussed.The requirements are intended to reduce risks to persons, the environment, and assets to the lowest levels that arereasonably practicable. This intent is achieved by using:a) seismic design procedures which are dependent on the exposure level of the offshore structure andthe expected intensity of seismic events;b) a two-level seismic design check in which the structure is designed to the ultimate limit state (ULS)for strength and stiffness and then checked to abnormal environmental events or the abnormal limitstate (ALS) to ensure that it meets reserve strength and energy dissipation requirements.Procedures and requirements for a site-specific probabilistic seismic hazard analysis (PSHA) are addressed foroffshore structures in high seismic areas and/or with high exposure levels. However, a thorough explanation ofPSHA procedures is not included.Where a simplified design approach is allowed, worldwide offshore maps, which are included in Annex B, show theintensity of ground shaking corresponding to a return period of 1 000 years. In such cases, these maps may be usedwith corresponding scale factors to determine appropriate seismic actions for the design of a structure.For design of fixed steel offshore structures, further specific requirements and recommended values of designparameters (e.g. partial action and resistance factors) are included in ISO 19902, while those for fixed concreteoffshore structures are contained in ISO 19903. Seismic requirements for floating structures are contained inISO 19904, for site-specific assessment of jack-ups and other MOUs in ISO 19905 (all parts), for arctic structures inISO 19906 and for topsides structures in ISO 19901-3.