API RP 2A-LRFD
Draft Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms - Load and Resistance Factor Design
|Publication Date:||15 December 1989|
The load and resistance factor design (LRFD) format of this practice is realiability based in constrast to the "Recommended Practice for Planning, Designing, and Constructing Fixed Offshore Platforms," 18th Edition, which based on working strength design (WSD) methods. In the RP2A-LRFD uncertainties that naturally occur in the determination of loads and member strengths are explicitly accounted for in the development of the LRFD format. The LRFD format of this practice also provides a framework for extrapolating the existing design practices into frontier areas where experience is limited.
While the load and resistance factors have been chosen based on reliability considerations, the designer is not faced with carrying out probabilistic calculations. This work was done during the development of the practice and is documented in PRAC-22 reports and summarized in the "LRFD Commentary" in this draft.
The design provisions of the RP2A-LRFD have been calibrated against the exisiting provisions of the RP2A-WSD. This assures that RP2A-LRFD designs will be based on the same extensive experience base existing in the RP2A-WSD. The calibration has included checking six existing or planned platforms with the LRFD provisions. The checks have included static, dynamic, and earthquake loadings.
The RP2A-LRFD is a self-contained document. When adopted it will not be necessary to refer to the RP2A-WSD when using the RP2A-LRFD. Almost all of the topics included in the present RP2A-WSD are covered in the RP2A-LRFD. Provisions for complaint, arctic, and gravity concrete structures are outside the scope of the present document.
Like the current RP2A-WSD, the RP2-LRFD is intended for design of new platforms, not for requalification of existing platforms. In cases of reanalysis, the better knowledge of loads and materials for existing platforms often justifies a more detailed and precise analysis. The load factors and formulas in RP2A-LRFD should not preclude the use of load factors and formulas specific to reanalysis, as long as consistent reliability can be demonstrated.