APi Rp-2A 20Th Edition Update: Seismic Topsides Design And Assessment Guidelines
Authors: Craig M.J.K. , DoIan D.K. , Turner J.W. 
Published: October 2008

API guidelines have been updated to assist with the mitigation of hazards due to undersized and inappropriately restrained deck appurtenances and equipment subject to earthquake loading. Guidance is provided for the design of ne w appurtenances and equipment, as well as for the assessment of the adequacy of existing facilities. Areas for continued improvement are identified. The significant dedication of those who have supported these API efforts is acknowledged.

PAST HISTORY - SEISMIC CRITERIA EVOLUTION

The recent changes in the seismic criteria section of API RP 2A-WSD 20th edition on improved guidance for the design and assessment of â??appurtenances' on the decks of platforms in earthquake areas mark one milestone in an evolving process of continued seismic design guidance improvement.

The status of today's API RP 2A-WSD earthquake related Section 2.3.6 and associated Commentary reflect an extraordinary history of dedication and effort of numerous people working under the umbrella of the API Committee 2 organization.

It is as a result of these efforts that API RP 2A's seismic design guidelines are the basis by which offshore oil and gas platforms are designed in earthquake-prone areas worldwide today. A brief history behind the development of the current version of 2A's seismic guidelines follows:

The first edition of API RP 2A in 1969 incorporated the Uniform Building Code criteria. In 1974, under the chairmanship of Al Knapp of Amoco, the API Seismic Criteria committee was formed. 1975 saw the first program at OTC devoted to seismic criteria and design.

Major improvements were made by the committee in 1977 under the chairmanship of Warren Mitchell of Chevron: The 8'h edition first established Strength and Ductility level ground motion intensities in a seismic risk map of US coastal waters. The â??generic' smoothed design response spectra tied to local soil conditions first appeared. Ductility level deflection requirements were established.

Through representation on the ACI 357 committee, in 1978 the ACI 357-R-78 adopted 2A's seismic criteria guidelines for concrete structures. The same year, the committee sponsored experimental cyclic inelastic studies of braced frames.

The 10th edition of RP 2A in 1979 incorporated the results of the Offshore Alaska Seismic Exposure Study - OASES - in the seismic risk map. Ductility level performance was specified in energy absorption capacity terms. In 1982, through committee representation on 2N, 2A's seismic design guidelines were incorporated into the first edition of API RP 2N for the design of arctic structures.

The commentary of the 14th edition was expanded in 1984 with detailed guidelines for site-specific seismic hazard evaluations. The committee sponsored seismic load effects studies whose results were input to the initial API LRFD efforts through PRAC project 85- 22. in 1987, the 17th edition provided detailed commentary and guidance on pile dynamic performance.

Early in 1991, improved platform topsides design and assessment guidelines were developed and are incorporated into the 20th edition of API RP 2AWSD (Section 2.3.6e.2 and C2.3.6e.2) and into the 1â??t edition of API RP 2A-LRFD (Sections C.4.4.2 and COM. C.4.4.2). An explanation of these guidelines is the focus of this paper.