On the determination of the primary part of the seismically induced inertial forces in pressurized piping systems
Résumé
This paper focusses on discussing which part of inertial stresses should be regarded as primary or secondary. To do so, a classification is established based on the study of non-linear oscillator. The case of zero and non-zero-permanent force are explored to simulate the pressure effect. Two types of dynamic signals are considered as samples of a wide-band and a narrow-band stochastic process to simulate ground level motions and floor input motions respectively. The results of the classification highlight the importance the φ parameter, the ratio between the natural frequency of the oscillator and the central frequency of the input motion, in the calculation of the primary part of the inertial forces. Based on the defined classification, a reduced spectrum method, initially proposed by Labbé and Nugyen [Modified Response Spectrum Accounting for Seismic Load Categorization as Primary or Secondary in Multi-Modal Piping Systems, ASME 2021, PVP] is tested numerically on a piping system. Non-linear calculations are compared to the results of the linear reduced spectrum analysis. Von-mises stresses at the most damaged elbow flank and opening/closing displacement of the same elbow are compared. Comparable results are obtained in term of stresses.
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