Through an ongoing effort by API / ISO (ISO/TC67/SC 7/ WG 3 /Panel 5) Earthquake Committees and feedback received from the petroleum and natural gas industries, the first edition of ISO 19901-2 - Seismic design procedures and criteria was published in April, 2004. ISO stands for "The International Organization for Standardization."
This paper highlights the new features of ISO 19901-2. They include worldwide offshore maps of site seismic zones, the new response spectrum shape, at least 4 sets of ground motion records will be required for the linear or nonlinear time history analysis. The site soil classifications have been expanded to include types A / B, C, D, E, and F in contrast to the soil types of A, B, and C used in API Earthquake Response Spectra. Also, the terms SLE (Strength Level Earthquake) and DLE (Ductility Level Earthquake) as used in API have been replaced by ELE (Extreme Level Earthquake) and ALE (Abnormal Level Earthquake) in ISO.
Three existing platforms located in the different seismic zones of the world are used to verify the ISO 19901-2 seismic design guidelines: i) API model - the 8-legged, 80 conductor, template-type structure designed for offshore California in 265 feet water, ii) A 4-legged, drilling and production platform with 8 skirt piles designed for offshore Trinidad in 497 feet water depth, iii) A 4-legged, template type wellhead platform designed for the Persian Gulf in 181 feet water depth. The API model was used in the 1980s under the sponsorship of API and coordination of API Earthquake Committee to verify the API Earthquake Design Provisions.
Through an ongoing effort by API / ISO (ISO/TC67/SC 7/ WG 3 /Panel 5, "Panel 5") Earthquake Committees and feedback received from the petroleum and natural gas industries, the first edition of ISO 19901-2 - Seismic design procedures and criteria was published in April, 2004. ISO stands for "The International Organization for Standardization."
ISO 19901 (Specific Requirements for Offshore Structures) consists of design criteria and design considerations for seven parts:
Metocean design and operating considerations,
Seismic design procedures and criteria,
Geotechnical and foundation design considerations,
Weight control during engineering and construction,
Stationkeeping systems for floating offshore structures and mobile offshore units.
ISO 19901 is one of a series of standards for offshore structures. The intent of ISO 19901 is to provide specific guidelines for other ISO 19900 series documents.
In this paper, we will concentrate on ISO 19902 (Fixed steel offshore structures) and ISO 19901-2 (Seismic design procedures and criteria) with regard to seismic design and analyses of offshore platforms. ISO 19902 is a very comprehensive design code (recommendations) for fixed steel offshore platforms, which is equivalent to API RP 2A (Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms). API RP 2A [Ref. 1 & 2] is a well-known and well-circulated design code (recommendations) in the offshore industry worldwide.