API REPORT GROUND MOTION
Ground Motion Intensity Factors and Acceleration Response Spectra Ninth Edition API RP 2A Earthquake Design Provisions Eastern Gulf of Alaska Region
|Publication Date:||1 November 1978|
This report documents a study of earthquake design criteria for the eastern Gulf of Alaska. This study backgrounded a portion of the development of the Ninth Edition of API RP 2A's Section 2.10 earthquake design guideline effective ground acceleration and response spectra.
This study was performed during 1976 and 1977, with additional details developed during early 1978.
This study is based on a statistical and probabilistic platform system performance analysis (risk or reliability analysis). In this analysis, an assessment was made of environmental exposures (oceanographic and seismic), the loadings imposed or induced in a given type of platform system, and the ability of the platform system (designed for given amounts of loading and according to API element sizing criteria) to resist such loadings. Environmental criteria parameters were determined from an assessment of reliabilities (for different design strategies) and cost impacts.
A conventional drilling and production, steel, tubular membered, pile supported, 12-leg, template-type platform for 300 feet of water, sited on soft and stiff soil profiles was used to characterize the platform system. Environmental conditions for the eastern Gulf of Alaska were studied. Elements of the platform (legs, braces, joints, piles) were sized according to the element sizing criteria contained in the Ninth Edition of RP 2A.
The results of this study are contained in two primary elements of the Ninth Edition RP 2A earthquake guidelines:
• Seismic zoning of the eastern Gulf of Alaska offshore area (Zone 5), and the associated effective ground acceleration (0.4 g), and
• Elastic response spectra appropriate for different soil conditions, and for calculation of elastic design forces (to be used in sizing platform elements together with API element sizing criteria).