The growth of the offshore industry into newer regions - including seismic regions - requires a detailed understanding of the earthquake design of offshore platforms. Guidance is provided in ISO 19901-2, " Petroleum and natural gas industries, Specific requirements for offshore structures, Seismic design procedures and criteria." This was adopted almost in it's entirely by API in 2013 in the form of API RP2EQ, " Seismic Design Procedures and Criteria for Offshore Structures." This paper provides supplemental information to these ISO and API standards with the intent to provide additional guidance to engineers analyzing and designing platforms in earthquake regions. The guidance is based on practical application of these standards over the past few years on platforms located in different worldwide regions. Issues discussed include: historical development of seismic guidelines; the importance of ductility in a platform design; Pushover and Time History analysis procedures; definitions of platform collapse; and, pre-planning for post-earthquake actions.

Historical Development of Offshore Platform Seismic Guidelines

Offshore platforms have been designed and installed in seismic regions since the 1960s when the first platforms were installed offshore California. These early structures used the onshore seismic design practice contained in the Uniform Building Code (UBC) of the time. The first specific guidance for seismic design for offshore platforms appeared in the API RP 2A (RP2A)" Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms," 1st Edition published in October 1969 and contained specific reference to the UBC including the calculation of an equivalent lateral seismic design load using a special structure design factor for offshore platforms. However, the guidance was limited to only a half page of the sixteen page document. The API RP 2A 3rd Edition issued in January 1972 maintained the UBC guidance but was the first to specifically also mention dynamic analysis as an option, although the guidance was limited to a small paragraph.

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