Seismic Analysis and Design of Buried Pipingby M. Bilgin Atalay, Cygna Group, Oakland, United States,
Abstract: Among the causes of damage to buried pipelines due to earthquakes, the one that is most complicated to analytically deal with and that is most credible at safety related sites such as nuclear plants is the wave propagation effect. The preliminary step in the analysis of stresses in a buried piping run due to wave propagation effects consists of data gathering and the establishment of the fundamental relationships. These include seismic loading parameters such as peak ground excitations, soil properties such as different moduli, wave velocities, friction parameters, etc. Equations, and tables are specified whereby the various parameters can be determined in a typical application. The analysis of stresses at various locations is performed next. A set of equations is presented whereby axial and bending stresses due to various wave types at long and short straight runs, elbows, tees, and building interfaces can be calculated. Guidance is provided whereby the stresses due to the seismic effects can be combined with the stresses due to other concurrent loads, and the combined stress can be compared with the design allowables. Among the practical design considerations for the mitigation of any possible overstress conditions are the uses of flexible couplings, the beneficial effects of the soil friction, removal of excess conservatisms in the analysis, and the use of more refined analysis techniques. Practical issues such as the presence of thrust blocks employed to satisfy the national fire protection code, and the possible use of plastic as the piping material are also discussed.
Subject Headings: Stress analysis | Soil analysis | Seismic loads | Seismic design | Buried pipes | Seismic tests | Parameters (statistics)
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