This part of ISO 19901 contains requirements for defining the seismic design procedures and criteria for
offshore structures; guidance on the requirements is included in Annex A. The requirements are applicable to
fixed steel structures and fixed concrete structures. The effects of seismic events on floating structures and
partially buoyant structures are also briefly discussed. The site-specific assessment of jack-ups in elevated
condition is only covered in this part of ISO 19901 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
discussed.
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 platforms exposure level 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 accidental limit state
(ALS) to ensure that it meets reserve strength and energy dissipation requirements.
For high seismic areas and/or high exposure level fixed structures, a site-specific seismic hazard assessment
is required; for such cases, the procedures and requirements for a site-specific probabilistic seismic hazard
analysis (PSHA) are addressed. However, a thorough explanation of PSHA procedures is not included.
Where a simplified design approach is allowed, worldwide offshore maps are included in Annex B that 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 f (...abbreviated)