Seismic-Resistant Design of Piping, Equipment, and Appurtenances for Offshore Structures

Abstract

ABSTRACT The requirements and procedures for seismic resistant design of offshore structures are receiving increased attention as sites are selected in seismically-active zones, and emphasis is usually on the basic structure. Of major importance to the entire facility, however, are the seismic design procedures used for piping, equipment, and appurtenances essential to operation and safety. Conventional static approaches used in some building codes generally neglect dynamic interaction between components and their supporting structure, and therefore are often inadequate. The paper provides a general overview of procedures which account for this dynamic interaction and which have been successfully applied to many types of facilities, including hazardous industrial facilities, nuclear plants, hospitals, conventional buildings, and offshore structures. The basic engineering principles of these procedures are applicable to all types of facilities, and only the details must be tailored to meet specific design and performance requirements. INTRODUCTION The requirements and procedures for earthquake resistant design of offshore structures are receiving increased attention as sites are selected in seismically-active zones. Emphasis is usually focused on the design of the basic structure. Of major importance to the entire facility, however, are the procedures used to ensure that critical piping, equipment, and other components essential to continued operation and safety can withstand the motions due to possible seismic events. Decisions regarding the extent of the design of such components will depend upon future regulatory requirements and management decisions regarding acceptable seismic risk. If, for example, a two-earthquake criterion is used, it may be necessary to design components used in normal processing operations, such as piping, pumps, compressors, heat exchangers, and separators to withstand the motions postulated for the lower level earthquake (e.g., strength level earthquake). It may also be necessary to design components essential for the safety of the facility, such as piping, equipment, and controls necessary for well shut-in, hazardous material storage, and fire protection systems, to resist motions specified for the upper level earthquake (e.g., ductility level earthquake). This paper presents a survey of viable procedures for designing critical supported components to withstand seismic loads, and is intended for managers, engineers, and equipment suppliers who interface with the seismic design of components. Since this is a survey paper, technical details of dynamic analysis methods are not presented; these are available in the literature. Emphasis is on seismic qualification of components by engineering design and analysis, which is often the most direct and economical solution. Certain items such as control panels and relays that are not amenable to analysis should be qualified by physical testing. This topic will be discussed in a future paper. Conventional static loading approaches such as those used in building codes often neglect dynamic interaction between supported component and supporting structure, and therefore may be inadequate in many cases. The dynamic approaches discussed in this paper consider this interaction.