Sophistication of seismic performance evaluation for plant structures utilizing finite element analysis of assembly modelling

Satoda, Akira*; Matsukawa, Keisuke*; Guo, Z. H.*; Choi, B. ; Nishida, Akemi  

In order to contribute to the seismic safety assessment of nuclear power plants and other industrial facilities against large earthquakes, it is an important issue to realistically capture the seismic behavior of plant structures and enable practical response analyses. Among the structural features that significantly influence seismic behavior, joints play a particularly critical role. In the case of steel pipe support structures (hereafter referred to as pipe racks), the joints connecting members (hereafter referred to as joints) have conventionally been modeled by empirical approaches, often idealized as pinned or rigid, leading to conservative evaluations. The final objective of this study is to develop a joint modeling method that reproduces more realistic behavior by utilizing three-dimensional detailed models of joints. To date, using the developed three-dimensional detailed analysis techniques, we have evaluated realistic semi-rigid stiffness of joints in both elastic and elasto-plastic ranges, proposed simplified joint models, and reported the obtained results. Furthermore, three-dimensional detailed analyses of an entire pipe rack including joints have been conducted, demonstrating the possibility of simultaneously capturing both the global seismic response of the pipe rack and the local joint behavior. In this paper, the simplified joint model proposed in previous studies is applied to the pipe rack joints modeled with conventional beam elements used in design practice, and the analysis results are compared with those of the detailed three-dimensional analysis. The findings are organized to clarify the differences and applicability. This enables improvement in the accuracy of practical seismic response analysis methods using beam elements. By applying the obtained results to the modeling of joints in steel structures of plant facilities, more rational seismic safety assessments of nuclear facilities and other plant structures can be expected.