Study on Piping Seismic Response Under Multiple Excitation

The uniform response spectrum (URS) analysis method is generally used to seismic qualification of piping systems in nuclear power plants (NPPs). This method can reasonably not only compute dynamic responses of the piping systems exposed to different seismic motions from the building but also tend to overestimate the responses due to an assumption while conservatively considering a variety of the characteristic among input loadings. Increases of design seismic motions for NPPs in Japan by 2–3 times due to the 2011 off Pacific Coast of Tohoku Earthquake resulted that structures, systems, and components such as piping systems are subject to numbers of additional supporting structures to meet the design code requirements. Use of multiple-input analysis methods (independent support motion methods) is expected to bring high degree of precision in dynamic responses than the URS method. However, existence of a handful of experimental tests prevents from utilizing the method in the design process for NPPs in Japan. In order to practically utilize the multiple-input analysis methods in the plant design, this paper provides validation analyses and results for the multiple-input analysis methods for piping by conducting excitation tests and validation analyses. Some recommendations were also found in the study for seismic design of NPPs.