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Adoption of Nonlinear Resonant Ultrasonic Spectroscopy for the Evaluation of Stress State on Concrete in Prestressed Beam

프리스트레스트 보의 콘크리트 응력 수준 평가를 위한 비선형 초음파 공진 기법의 적용

  • Kim, Gyu-Jin (Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology) ;
  • Kwak, Hyo-Gyoung (Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology)
  • 김규진 (한국과학기술원 건설 및 환경공학과) ;
  • 곽효경 (한국과학기술원 건설 및 환경공학과)
  • Received : 2017.02.15
  • Accepted : 2017.03.14
  • Published : 2017.06.30

Abstract

In order to evaluate a stress state of concrete according to the change of tensile force of prestressed beam, improved nonlinear resonant ultrasonic spectroscopy(NRUS) method is proposed. This technique is advantageous to evaluate the stress state in initial state because the method shows much higher sensitivity than existing linear ultrasonic methods. The NRUS technique measure a nonlinearity parameter, which is calculated from the resonant frequency shift of ultrasonic wave related to the medium state, and the result is also closely related to the stress state of concrete. In this study, the nonlinearity parameter was measured with the change of tensile force to verify the close relationship between the two factors, and the effect of repetitive load cycle on the change of nonlinearity parameter was analyzed. In addition, sensitivity comparison with the linear ultrasonic pulse velocity method was performed. Through the experimental results, the possibility of NRUS technique for the evaluation of stress state in prestressed beam was confirmed.

프리스트레스트 보의 인장력 변화에 따른 콘크리트 응력 수준을 평가하기 위하여, 초음파를 이용하는 기존의 방법보다 개선된 비선형 초음파 공진 기법의 도입을 제안하였다. 이는 동일하게 초음파를 사용하는 선형의 기법보다 월등히 높은 민감도를 보이므로 초기 상태의 응력 평가에도 유리하다. 비선형 초음파 공진 기법은 초음파 통과시 매질 상태에 따른 공진 주파수의 변화의 정도로부터 계산되는 비선형 인자의 값을 측정하며, 측정 결과는 콘크리트의 응력 상태와도 밀접한 연관을 갖는다. 본 연구에서는 유압 펌프를 통한 인장력 작용에 따른 비선형 인자의 측정을 수행함으로써 두 인자 사이에 밀접한 연관성이 있음을 확인하고, 반복적인 하중 이력의 작용이 비선형 인자의 변화에 미치는 영향을 분석하였다. 추가적으로, 선형 초음파 전파 속도 측정 결과를 비교하여 제안한 방법의 민감도를 검증하였다. 측정 결과를 통해 프리스트레스트 보의 콘크리트 응력 수준 평가를 위한 비선형 초음파 공진 기법의 적용 가능성을 확인하였다.

Keywords

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