Historical Development And Assessment Of The Current Api Design Methods For Axially Loaded Pipes
Authors: Pelletier J.H. , Murff J.D. , Young A.C. 
Published: October 2008

ABSTRACT
The design methods for axially loaded piles contained in the API RP 2A, Recommended Practice for Planning. Designing and Constructing Fixed Offshore Platforms are continually evaluated and updated. To support this activity, API has funded research over the past 10–12 years which has resulted in the establishment of an internationally recognized data base of axial pile load tests. Subsequent interpretation of these data led to significant changes in the design methods for axially loaded piles for both sand and clay. The sand revisions, first incorporated into the 15th Edition of RP 2A provide improved statistical predictions (bias and coefficient of variation) of the sand data base than did the design methods for sand contained in earlier editions. The clay revisions, first incorporated into the 17th Edition of RP 2A provide a statistical description of the clay data base that is similar to descriptions provided by earlier clay methods. Both the revised clay and sand methods provide a more technically sound framework than the methods contained in earlier editions. The revised methods are contained in the current, i.e., the 20th Edition of RP 2A (1993). These revisions have initiated considerable debate, and have prompted the authors to present their thoughts herein. A discussion of the data base, review of the philosophy and evolution of the design method, and a summary and analysis of the key criticisms are provided. The data have been exceedingly useful in formulating design practice, but in our opinion they are too limited to conclusively resolve many of the important issues. While some modifications to the present practice seem to be indicated, the authors believe that when combined with a careful site investigation, attention to installation detail and good engineering judgment, RP 2A continues to provide a sound basis for design of axially loaded piles.

INTRODUCTION
The empirical design methods for axially loaded piles contained in the 20th Edition of RP-2A (1993) evolved over a number of years and are subject to continuing review and updating. This process led to significant changes in the design criteria for piles in both sand (15th Edition 1984) and clay (17th Edition 1987). The revisions have given rise to several years of international discussion among engineers, government agencies, API, and certification authorities as to the applicability of the revised methods, especially for sites outside the Gulf of Mexico.
In this paper we first describe the role and history of W 2A, including summaries of selected relevant studies. Similar histories were presented by Focht (1983) and Toolan and Horsnell (1992), but some repetition is given here for completeness and continuity. This history includes important research findings that impact unresolved design issues. This discussion is followed by a brief analysis of each of these issues. Finally we present our own views of the validity of the current RP 2A pile design methods and our comments on their future evolution.