Seismic analysis of multiply supported piping systems

The analysis of piping systems subjected to different response spectra input at different supports has been a subject of intense discussion in recent years. Although it is well known that the envelop response spectra analysis technique is often too conservative, no acceptable guidelines have emerged to allow the use of the multiple support input response spectra technique on a consistent basis. Since actual piping systems are generally supported by several support structures, such as vessel and steel structures, it is important to qualify multiple support input response spectra analysis techniques so that realistic piping design can be achieved. The overall reliability of the plant can be improved by using realistic seismic criteria in design to reduce the unnecessary conservatism. In this study, aided by the comparison of analytical and test results, a practical approach of forming the groups along with the use of square-root-of-sum-of-squares (SRSS) combinations groups is presented. The effects from closely spaced modes and residual modes are examined also. Most importantly, the adequacy of using the multiple support input response spectra analysis method with Code Case N-411 damping in the actual piping design is demonstrated. One of the major conclusions from this test correlation analysis is that the multiple support input response spectra method using SRSS combination between groups, Code Case N-411 damping and ±15% spectrum peak broadening is more realistic and should be acceptable for the design of piping systems. 26 refs., 26 figs., 49 tabs