Response Combination Method Between Dynamic, High Frequency and Pseudo-Static Responses With Floor Response Spectrum Method Assisted by Time History Analysis for Multiply Supported Piping System

Abstract

Abstract The independent support motion (ISM) response spectrum method is currently used for multiply supported nuclear piping system. This method requires calculating and combining maximum values of following three responses excited by independent inputs of support excitations: the dynamic response of each mode below the cutoff frequency, the rigid response of the high frequency mode above the cutoff frequency (high frequency response), and the pseudo-static response due to relative displacement at the support point. Here, although the maximum values of each response rarely occur simultaneously, it is difficult to combine each maximum response appropriately because phase information is lost in the response spectrum analysis method. NUREG-1061 issued by the U.S. NRC proposes, based on the analysis results of many multiply supported piping systems, a method that mainly uses the absolute sum rule when combining the maximum values of the dynamic responses by multiple excitations and the SRSS rule when combining the maximum value of the pseudo-static response with the dynamic response. Even with this method, however, it is difficult to avoid excessive overestimation. The authors have already developed an analysis method for multiply supported piping systems, named SATH method (Spectrum method Assisted by Time History analysis), which combines the maximum value of each dynamic response by each excitation considering the correlation between each response, and have presented it in ASME PVP2020, etc. Then, the SATH method has been improved to add the function that considers the correlation coefficients to the combination of the maximum values of the dynamic response, the high frequency response and the pseudo-static response using the time history acceleration and the time history displacement of each support excitation. In this paper, the combination method between the dynamic response, the high frequency response and the pseudo-static response in the SATH method is explained, and the advantages of the SATH method is confirmed by comparing the analysis results by the SATH method, by the currently used analysis method (NUREG-1061 method) and by the time history analysis method. The SATH method is found to yield results close to those of the time history analysis method and to avoid excessive overestimation.