# Validation of Seismic Performance of Stainless Press-to-Connect Piping System under Cyclic Loadings
## 5 Validation and Verification of FE Large Scale Piping System Model  
Experimental tests of large-scale piping systems are typically time-consuming and costly. To overcome these issues, it is necessary to develop a high-fidelity simulation model based on an experimental test to understand the in- or out-of-plane behavior of the piping system. Considering the material properties of the component-level test data, the bilinear kinematic hardening plasticity model as a nonlinear behavior material model was used to construct a high-fidelity FE simulation model of the large-scale piping system with a press-to-connect system. This large-scale piping system consisted of an upper elbow, a low elbow, a T-joint, and two flexible couplings to absorb energy from an earthquake. Based on the schematic design and experimental test of the piping system, a high-fidelity simulation FE model with the components was developed, and to allow seismic sway, the displacement and rotation in the z-direction were unfixed, as demonstrated in Figure 9. \begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{2}{c}{**Level**} \\ \cline{2-3}  & **Special** & **I** & **II** \\ \hline Drift ratio & 0.010 h & 0.015 h & 0.020 h \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Allowable inter-story drift ratio for KBC 2016. \begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{2}{c}{**Risk Category**} \\ \cline{2-3}  & **IV** & **III** & **I or II** \\ \hline Drift ratio & 0.010 hxx & 0.015 hxx & 0.020 hxx \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Allowable inter-story drift ratio for IBC 2015. Figure 8: Test setup of a large-scale press-to-connect piping system: (**a**) experimental set up; (**b**) cyclic loading protocol. Additionally, to describe the characteristics of the T-joint in the piping system as a press-to-connect system, both S3 and S4R shell elements were utilized, and other piping components such as the straight pipe, elbows, and flexible couplings were constructed using the S4R shell element in the ABAQUS platform [11]. Thus, a total of 31,751 and 32,360 elements and nodes were generated in the high-fidelity simulation model, respectively. Next, the results of the analytical model of the piping system were validated using the experimental test results. The characteristics of the seismic performance of the elbow joints with a press-to-connect pipe were extensively focused on in this study because the elbow is the weakest component in the piping system during and after a strong earthquake. Therefore, reconciliation of the experimental and numerical results at the elbow was the main priority in this study. First, the von Mises stress of the large-scale piping system was verified, as shown in Figure 10. The results of the high-fidelity simulation FE model are in good agreement with the data observed from the experimental test. The maximum and minimum stresses of the large-scale press-to-connect piping system is described in Figure 10c. The maximum von Mises stress of the FE model in the piping system and the stress from the experimental test at the lower press-to-connect elbow were 187 and 205 MPa, respectively, at the 10 th cycle during the loading condition. In addition, the observations from the upper elbow system, that is, the stresses of the FE model and experimental test, were 371 MPa and 403 MPa, respectively. In the case of the stress analysis, the error of the stress for the validation of the piping system model was less than 9%, which indicated that the FE model of the press-to-connect large-scale piping system using the ABAQUS platform [11] was a high-principled model. In particular, during and after a strong earthquake, the seismic sway to validate the FE model with the more critical condition was also an important phenomenon in the structural and nonstructural components. Figure 11 illustrates the deformation angle of the two-elbow system obtained from experimental and analytical data. The deformation angle results of the experimental and analytical models were not significantly different.