Combination of the primary and secondary stress components for piping systems

The study considers several typical piping models subjected to distinct support motions. The independent time history analysis yields both primary stresses due to inertia and secondary stresses due to relative support motions. In addition, this analysis predicts the total response due to both effects. These results presumably are the best estimate of the actual response of a piping system subjected to a real earthquake because the analysis involves solving the system equations at every time step and the phasing during the process of solution is not lost. The piping models were then analyzed using the response spectrum method to obtain the maximum primary stresses. The secondary stresses were next calculated by performing a set of static analysis which result in the most unfavorable combination. These two results are combined by both SRSS and absolute sum methods and the results are compared with the time history solutions. It was found that the SRSS combination of the primary and secondary stress components yield acceptable results provided the latter component is calculated in its most unfavorable combination. (orig./HP)