Journal of the Korea Academia-Industrial cooperation Society (한국산학기술학회논문지)

The Korea Academia-Industrial cooperation Society (한국산학기술학회)
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Probabilistic Fatigue Life Evaluation of Steel Railway Bridges according to Live-Dead Loads Ratio

강철도교의 활하중-사하중 비에 따른 확률기반 피로수명 평가

  • Lee, Sangmok (School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology) ;
  • Lee, Young-Joo (School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology)
  • 이상목 (울산과학기술원 도시환경공학부) ;
  • 이영주 (울산과학기술원 도시환경공학부)
  • Received : 2018.11.11
  • Accepted : 2019.01.04
  • Published : 2019.01.31
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Abstract

Various studies have been conducted to evaluate the probabilistic fatigue life of steel railway bridges, but many of them are based on a relatively simple model of crack propagation. The model assumes zero minimum stress and constant loading amplitude, which is not appropriate for the fatigue life evaluation of railway bridges. Thus, this study proposes a new probabilistic method employing an advanced crack propagation model that considers the live-dead load ratio for the fatigue life evaluation of steel railway bridges. In addition, by using the rainflow cycle counting algorithm, it can handle variable-amplitude loading, which is the most common loading pattern for railway bridges. To demonstrate the proposed method, it was applied to a numerical example of a steel railway bridge, and the fatigue lives of the major components and structural system were estimated. Furthermore, the effects of various ratios of live-dead loads on bridge fatigue life were examined through a parametric study. As a result, with the increasing live-dead stress ratio from 0 to 5/6, the fatigue lives can be reduced by approximately 30 years at both the component and system levels.

강철도교에 대한 확률기반 피로 수명 평가를 위한 많은 연구들이 그간 있어 왔지만, 대부분 상대적으로 단순한 피로 균열 진전 모델을 기반으로 한 연구들이었다. 이 모델은 최소 응력이 0이고 일정한 응력변동 진폭을 가정하기 때문에, 철도교의 피로수명 평가에는 적합하지 않다. 따라서 본 연구에서는 보다 고도화된 균열 진전 모델을 이용해 강철도교의 피로 수명을 평가하는 새로운 확률기반 기법을 제안하였다. 또한 이 기법은 철도교에서 흔히 발생하는 다양한 하중 변동 진폭을 rainflow cycle counting algorithm을 사용해 고려할 수 있어, 보다 현실적인 피로 수명을 평가할 수 있다. 제안된 기법을 강철도교 예제 모델에 적용하여 피로 수명을 주요 부재 및 시스템에 대해 평가하였다. 또한 다양한 활하중-사하중 비가 피로 수명에 끼치는 영향을 분석하였으며, 그 결과 활하중-사하중 응력 비가 0에서 5/6까지 증가함에 따라 부재와 시스템 수준 모두에서 피로 수명이 30년 내외까지 줄어드는 것을 확인하였다.

Keywords

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Fig. 1. Cyclic loading for various values of R

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Fig. 2. Steel railway bridge example

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Fig. 3. Stress history for Members 13 and 27

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Fig. 4. Reliability indices for five selected members obtained via proposed method (R=3/4)

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Fig. 5. Reliability indices for two selected members and the entire system, as derived via the proposed method

Table 1. Maximum stress values of the five structural members with the overall highest stress values

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Table 2. Statistical properties of random variables (RVs)

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Table 3. Statistical properties of random variables

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