API RP2EQ - Seismic Design Procedures and Criteria for Offshore Structures

Abstract This paper describes the updates of the API recommended practice for seismic design procedures and criteria for offshore structures. The updates are divided into two parts. The first part is a new API Recommended Practice (RP) called API RP 2EQ which contains the overall seismic design procedures and selection of seismic design criteria, applicable to all types of offshore structures. This is a modified version of ISO 19901-2 adjusted as necessary for the USA. The second part is an update to API RP 2A (RP2A) or seismic design practices for steel jackets, that follows a combination of prior RP2A practices as well as the guidance contained in ISO 19902 (steel jackets). This paper describes these updates and in particular discusses how the changes differ from prior API practice. The updated seismic documents are part of an overall API effort to update RP2A as well as merge and align with the worldwide ISO documents. Background The original API RP 2A seismic design procedures were developed in the 1970's and early 1980's for fixed steel structures offshore California and Alaska. There have been few updates to these design procedures since then. However, during this time, there was considerable effort by the onshore building industry and the International Standard Organization (ISO) to develop new seismic design procedures and guidance. Much of the onshore industry work was an outcome of lessons learned from large seismic events like the 1985 Michoacan earthquakes that affected the Mexico City area, the 1989 Loma Prieta earthquake in the San Francisco Bay area, the 1994 Northridge earthquake in the Los Angeles area and the 1995 Hyokogen- Nanbu earthquake in the Kobe area. These earthquakes resulted in damage and destruction of various types of structures, some of which had been designed to what was thought at the time to be adequate seismic design standards.