Application of Seismic Fragility of Buried Piping Systems with Bellows Expansion Joints

Bellows expansion joints are known to have a large displacement capacity and can thus be potentially used to improve the seismic performance of buried piping systems. However, there are no guidelines on the installation of bellows expansion joints for the seismic performance improvement of buried piping systems. Furthermore, there are very few studies on the seismic performance of buried piping systems with bellows expansion joints. In this study, therefore, we performed seismic fragility analysis according to the installation conditions to obtain basic data for the installation guidelines of bellows expansion joints. Therefore, in this study, an experimental test was performed on bellows expansion joints considering the characteristics of earthquake loading conditions, and a 3D finite element (FE) model using the ABAQUS platform was developed and validated based on the experimental results. This model was verified by comparing the force-displacement relationship and energy dissipation. Leakage occurred at a displacement of 113.6 mm in the experiment, and the FE analysis result was also applied up to the same displacement. In the case of energy dissipation, an error between the FE model and experimental result was determined not to be significant. However, the appearance of such physical performance errors is due to the manufacturing errors resulting from the bellows forming process and the variability of material properties. Finally, seismic fragility analysis of buried pipeline systems with bellows expansion joints was performed. In addition, the following cases were used for analysis according to whether bellows were applied or not: (1) without a bellows expansion joints; (2) with a single bellows expansion joint; and (3) with two bellows expansion joints. In conclusion, it was found that the seismic performance of the buried pipeline system was improved when bellows were applied. However, the effect of the seismic fragility curve according to the increase in the number of bellows was insignificant.