This paper provides investigation on method of an elasto-plastic analysis for practical seismic design of nuclear piping systems, which are excited by multi-direction input.
The Japan Society of Mechanical Engineers (JSME) established a task group to develop an elasto-plastic analysis method for nuclear piping systems, and prepared a case example code proposal for JSME., Our studies in past (ASME PVP2016-63186 and ASME PVP2017-65341) were implemented on tests with unidirectional excitation using simple piping systems. In order to examine the applicability of the proposed case example code for JSME in piping of actual systems, it is necessary to examine cases in which there is multidirectional input excitation in piping systems in scales comparable to those of the piping in actual systems. We therefore conducted an analytical examination on demonstration of “the ultimate strength of piping system,” which was implemented at NUPEC. 
We confirmed in the results of analytical examination that the strain range could be calculated at precision nearly equivalent to our examinations in the past, and that the draft code case was applicable. However, we also found a problem which needs to be solved.
In addition, we were able to confirm that the local damping increase caused by the elasto-plastic behavior of the elbow which was subject to examination in this study was 1% or larger.