PERFORMANCE EVALUATION ON JOINTED PIPES USED UNDERGROUND FOR FIRE PROTECTION AT A NUCLEAR POWER PLANT AS A RESPONSE TO THE EFFECTS OF THE 2007 NIIGATA-KEN CHUETSU-OKI EARTHQUAKE

摘要

This study discusses the strength of jointed pipes used underground for fire protection at a nuclear power plant and their capacity to accommodate ground displacement. For this purpose, bending tests, a finite element analysis and an elastic beam theory analysis were conducted. The bending tests were conducted for four types of joints previously subjected to actual use, including welded, flange, screw and coupling types. The welded and flange joints demonstrated significantly higher load capacity; five times that of the coupled joint. The bending test results for the flange, screw and coupling joints were applied to identify the bending moment and rotation angle at the moment the internal pressure reached the level of the atmospheric pressure due to leakage. The limit state of the welded joint was not obtained in the experiment but was estimated by nonlinear finite element analysis. The bending moment and rotation angle of the welded joint were identified at the moment the welded joint reached the limit state. Finally, the test results and finite element analysis were applied to estimate the capacity of each joint to accommodate ground displacement. The elastic beam theory was used by modeling the pipe as an elastic beam and idealizing the joint as an elastic rotational spring. Consequently, the ground displacement capacity of the welded joint exceeded that of the coupling and screw joints by more than 500 per cent.