This paper summarizes current developments in the International Standards Organization (ISO) proposed guidelines for design of offshore platforms to resist earthquakes. These developments include updated evaluations of seismic exposures in the U.K. and Norwegian Sectors of the North Sea, offshore Japan and Indonesia, and in the Bay of Campeche Mexico. Guidelines have been developed to permit design analyses based on either 100-year or 200 year bases. Recent results from measurements and analyses of the effects of local soil and geologic conditions are used to update the proposed ISO guidelines. Updated developments also address steel and concrete elements in offshore platforms. Both 'fixed' and 'information sensitive' load and resistance factors for steel and concrete elements have been developed to increase the ease of use of these guidelines. The updated guidelines in this paper provide important improvements in development off reliability based criteria for design and requalification of fixed offshore platforms. These improvements are in characterizations of seismic exposure, effects of local soil and geologic conditions on ground motions, performance characteristics of steel and concrete elements and pile and mat foundations subjected to earthquake loading effects, and in characterization of dynamic loading effects in fixed offshore platforms subjected to ultimate limit state earthquakes.
A first-generation LRFD ISO guideline for design of steel, pile supported, template-type platforms to resist earthquake induced loading has been developed.1 This guideline was based on the API RP 2A LRFD guideline and on the collective experience and judgment of the ISO TCG7-WG3-P5 committee members. During the first generation developments, limited verification studies of the entire process were performed, there was limited documentation of the background for some of the key developments, and there were additional topics that needed to be addressed. Three general topics are addressed in this paper:
seismic exposure characteristics,
design response spectra characteristics,
concrete gravity base structure characteristics.
