With five decades of construction and project management experience as a civil engineer, split equally between the public and private sectors involving projects with a total value of several hundred billion (US$s); my goal has always been to deliver solutions that are customer focused and performance that adds value.

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During the late 1980's it became evident that an API process was required for assessing the structural integrity of existing jacket platforms in the US OCS. The approach would be different from the design of new platforms and as such required a new section of API RP 2A. The offshore community then established an API working group that developed the assessment approach and released it in the mid 1990's as "API RP 2A, Section 17 - Assessment of Existing Platforms." The background and assumptions of Section 17 are described in a series of 1994 OTC papers. Since then, Section 17 has become the worldwide recognized approach for assessing existing platforms. It has been used many times around the world and particularly in the Gulf of Mexico. In August 2003, the MMS released an NTL requiring Gulf of Mexico platform owners to assess their platforms to Section 17 requirements. This paper provides further background, clarifications and proposed updates to Section 17. The paper is divided into three parts. Part I is a discussion on the background and perspective on why and how Section 17 was originally developed including review of some of the basic premises of the document. Part II is a historical perspective on how Section 17 has been implemented over the past seven years, and how platforms that applied the process have performed, including during Hurricane Lili. Part III presents the planned future of Section 17 and proposed clarifications and updates. Part I: The Development of Section 17 The offshore industry started in the Gulf of Mexico in the late 1940's. Drilling and production grew steadily into the 1960's. In the frontier environment where little was know about the details of wave heights and wave loadings, land based practices were extrapolated with apparent success. Various oil companies and contractors developed staffs and procedures to design, install and operate the necessary facilities. The industry had continued success until the early 1960â??s when Hurricanes Hilda in 1964 and Betsy in 1965 swept through the Gulf of Mexico resulting a considerable damage to and loss of a number of platforms. These were the first large scale ("full population") hurricanes that the industry had experienced and it was evident that some guidance was required for platform design. The First API Recommended Practice Following Hurricane Hilda, a group of industry leaders met to discuss issues related to design practice (13). Discussions of return periods for design wave height were one of the key topics. Considerable variance, from 25 year to 100 year periods, was confirmed along with a wide variety of techniques and data for determining the height for a given return period. Additional topics of key importance identified were steel design and foundation characteristics. More important than the actual topics discussed, was the long term result of the meeting. This group of more than 60 met in November 1964 and held what became the first meeting that eventually led to the issuance of the first design guidance for offshore facilities, the API Recommended Practice for the Planning, Design, and Construction Fixed Offshore Platforms in 1969, a 16 page document (11).

Design of steel offshore structures has traditionally been based on elastic analysis to determine the distribution of forces through the structure, for an envelope of design cases. Checks are then performed on a component basis to ensure that no element of the structure fails to meet the governing criteria. Uncertainties in estimating the design loads and component strengths are allowed for by the application of safety factors. The analyses undertaken are linear and take no account of the reserve strength, and the robustness of the system. This paper discusses how the use of X-bracing leads to more robust designs that are: lighter, less expensive to fabricate and easierto install. In this paper we will use the results of previous studies, [1,2] and a number of pushover analysis on two, third generation (1990's), central North Sea platforms, to show that:The .....use of X-bracing..." [3] increases structural robustness in the jacket, without sacrificing cost, or constructability.Omitting the horizontal members on the vertical framing will not compromise the robustness of an X-braced jacket, subjected to hydrodynamic loading, if adequately designed X-braced horizontals are used. Introduction The main aim of structural design and fitness for purpose assessment is to ensure that a structure adequately fulfills its requirements with respect to serviceability and safety. Most offshore jacket structures possess an inherent reserve strength that is greater than the strength of the critical components. This is derived from a variety of sources, the principal one being the nonlinear structural interaction between components through plastic deformation and load redistribution, which in redundant systems allows mobilization of alternative load paths. Some structures display considerable levels of reserve strength whereas others suffer from a sudden drop in capacity as soon as one critical member fails. The reduction in ultimate capacity of a jacket structure due to damage to individual members can be measured by the so-called Damage Strength Ratio (DSR). This is effectively identical to the Reserve Strength Ratio (RSR), but is calculated with specific member(s) removed. DSR analyses have been used to prioritize inspection and also to check the strength or reliability implications of damage events. As the industry moves towards system based design it is important during the design cycle that the reliability of different framing configurations be assessed. In this paper we examine the results of several pushover analyses performed for two platform designs which were selected to have similar water depth, deck payload, hydrodynamic loading and vertical framing but different horizontal framing patterns. The discussion will focus on the advantages of considering system behavior, and robustness at the conceptual design level without compromising steel weight, fabrication and inspection costs. Consideration will also be given to the effects of structural robustness on inspection/repair philosophy, and changes in operational requirements during the design life. Definitions Redundancy Fixed offshore structures are typically statically indeterminate, When the number of unknown forces and/or moments in a structure exceeds that which can be determined by statics, the structure is said to be indeterminate. The forces and/or moments that cannot be determined using statics are said to be superfluous or redundant.

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