Kommittébeteckning: SIS/TK 289 (Gassystem)
Källa: CEN
Svarsdatum: den 30 mar 2020
Se merSe mindre

This document contains requirements for defining the seismic design procedures and criteria for offshore

structures; guidance on the requirements is included in Annex A. The requirements focus on fixed steel offshore

structures and fixed concrete offshore structures. The effects of seismic events on floating structures and partially

buoyant structures are briefly discussed. The site-specific assessment of jack-ups in elevated condition is only

covered 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 as

liquefaction, slope instability, faults, tsunamis, mud volcanoes and shock waves are mentioned and briefly


The requirements are intended to reduce risks to persons, the environment, and assets to the lowest levels that are

reasonably practicable. This intent is achieved by using:

a) seismic design procedures which are dependent on the exposure level of the offshore structure and

the 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 limit

state (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 for

offshore structures in high seismic areas and/or with high exposure levels. However, a thorough explanation of

PSHA procedures is not included.

Where a simplified design approach is allowed, worldwide offshore maps, which are included in Annex B, show the

intensity of ground shaking corresponding to a return period of 1 000 years. In such cases, these maps may be used

with 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 design

parameters (e.g. partial action and resistance factors) are included in ISO 19902, while those for fixed concrete

offshore structures are contained in ISO 19903. Seismic requirements for floating structures are contained in

ISO 19904, for site-specific assessment of jack-ups and other MOUs in ISO 19905 (all parts), for arctic structures in

ISO 19906 and for topsides structures in ISO 19901-3.