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Title |
Structural Integrity Limit Evaluation of 3-Inch Steel Pipe Elbows under Seismic Loading
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Authors |
김성완(Sung-Wan Kim) ; 윤다운(Da-Woon Yun) ; 전법규(Bub-Gyu Jeon) ; 장성진(Sung-Jin Chang) ; 박동욱(Dong-Uk Park) |
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DOI |
https://doi.org/10.11112/jksmi.2026.30.5.75 |
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Keywords |
인터페이스 배관시스템; 구조 건전성 한계; 강관 엘보; 극저주기 피로 Interface piping system; Steel pipe elbow; Structural integrity limit; Ultra-low cycle fatigue |
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Abstract |
This study evaluates the ultra-low-cycle fatigue (ULCF) behavior and structural integrity limit of a 3-inch steel pipe elbow used in the secondary piping system of a nuclear power plant equipped with a seismic isolation system under extreme seismic loading conditions. The interface piping system connecting seismically isolated and non-isolated structures must accommodate large relative displacements during an earthquake, resulting in concentrated large plastic deformation and cross-sectional ovalization of the elbow component. To simulate this behavior, a 3-inch elbow specimen was fabricated, and dynamic cyclic loading tests were conducted by amplifying the seismic load from 100% to 355%. A modified Park?Ang damage index was introduced to evaluate the structural integrity limit in the ULCF regime by comprehensively considering ductility damage and energy dissipation damage. Calibration based on the experimental data yielded weighting coefficients of 0.58 and 0.42 for the ductility and energy terms, respectively. The results indicate that a structural integrity assessment based solely on a maximum-deformation-based ductile failure criterion may not adequately quantify the actual damage state in the ULCF regime. Under extreme seismic loading conditions, the structural integrity limit should therefore be evaluated by considering both ductility exhaustion and energy dissipation associated with the cyclic plastic loading history. Accordingly, this study proposes a physically sound methodology for evaluating the structural integrity limit of pipe elbows subjected to extreme seismic loading.
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