Journal of the Korean Geotechnical Society (한국지반공학회논문집)

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Laboratory Experiments for Evaluating Dynamic Response of Small-scaled Circular Steel Pipe

실내 실험을 통한 소형 모형 원형 강관의 동적 반응 평가

  • Song, Jung Uk (School of Architecture and Civil Engrg., Korea Univ.) ;
  • Lee, Jong-Sub (School of Architecture and Civil Engrg., Korea Univ.) ;
  • Park, Min-Chul (School of Architecture and Civil Engrg., Korea Univ.) ;
  • Byun, Yong-Hoon (School of Agricultural Civil & Bio-Industrial Engrg., Kyungpook National Univ.) ;
  • Yu, Jung-Doung (School of Architecture and Civil Engrg., Korea Univ.)
  • 송정욱 (고려대학교 건축사회환경공학부) ;
  • 이종섭 (고려대학교 건축사회환경공학부) ;
  • 박민철 (고려대학교 건축사회환경공학부) ;
  • 변용훈 (경북대학교 농업토목.생물산업공학부) ;
  • 유정동 (고려대학교 건축사회환경공학과)
  • Received : 2018.11.12
  • Accepted : 2018.11.19
  • Published : 2018.11.30
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Abstract

For a marine bridge foundation construction, a large-circular-steel-pipe has been proposed for supporting vertical load and preventing water infiltration. However, a ship collision can adversely affect the structural stability. This paper presents a fundamental study on dynamic responses of the large-circular-steel-pipe by an impact load. In laboratory experiments, small-scaled steel pipe is installed in a soil tank. The soil height and water level are set to 23 cm and 25~70 cm, respectively. The upper part of the steel pipe is impacted using a hammer to simulate the ship collision. The dynamic responses are measured using accelerometers and strain gauges. Experimental results show that the strain decreases as the measured location is lowered. The higher frequency components appear in the impact load condition compared to the microtremor condition. However, the higher frequency components measured at the strain gauge located below the water level do not appear. For the accelerometer signal, the maximum frequency under the impact load is higher than that of the microtremor. The maximum frequency decreases as water level increases but it is larger than the maximum frequency of the microtremor. This study shows that strain gauge and accelerometer can be useful for evaluating the dynamic responses of large-circular-steel-pipes.

최근 해상 교량 기초 시공 중 차수 및 연직 하중을 지지하는 역할을 수행하는 대형 원형 강관 가설 공법이 제안되었다. 하지만, 대형 원형 강관의 시공 및 운용 중에 발생할 수 있는 선박 충돌과 같은 위부 요인은 구조물의 안정성에 악영향을 줄 수 있다. 따라서, 본 연구에서는 외부 충격에 의한 대형 원형 강관의 동적 반응을 평가할 수 있는 기법을 개발하기 위해 실내 실험을 통한 기초 연구를 수행하였다. 실내 실험에서는 해상에 설치된 대형 원형 강관을 모사하기 위하여 소형 모형 강관을 토조에 설치하였고, 토조 속 흙의 높이와 수위는 각각 23cm와 25cm로 설정하였다. 수위는 40cm, 55cm, 70cm로 변화시켜가며 실험을 수행하였다. 선박 충돌을 모사하기 위하여 모형 강관의 상부를 해머로 타격하였으며, 모형 강관의 길이 방향으로 설치된 변형률계와 상부에 설치된 가속도계로 신호를 측정하였다. 실험결과, 변형률계로 측정된 변형률이 모형 강관의 상부에서 하부로 내려갈수록 감소하였다. 변형률계로 측정된 신호의 주파수는 충격이 가해지면 상시미진동 주파수보다 크게 증가하였지만, 수위 아래에 위치한 변형률계에서 측정된 주파수는 큰 증가를 나타내지 않았다. 가속도계로 측정된 신호의 최대 주파수는 충격이 가해지면 상시미진동 주파수보다 크게 증가하였다. 수위가 증가하면 최대 주파수는 감소하지만, 상시미진동 주파수보다는 크게 나타났다. 본 연구의 결과는 변형률계와 가속도계가 대형 원형 강관의 동적 반응 특성을 평가하는데 유용한 지표가 될 수 있음을 보여준다.

Keywords

GJBGC4_2018_v34n11_81_f0001.png 이미지

Fig. 1. Installation procedure of large-circular-steel-pipe (Ssenyondo et al., 2017)

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Fig. 2. Schematic diagram of wheatstone bridge circuit

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Fig. 3. Measurement system

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Fig. 4. Schematic diagram of small-scaled circular steel pipe installed in soil tank

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Fig. 5. Normalized strain according to gauge location at different water levels

GJBGC4_2018_v34n11_81_f0006.png 이미지

Fig. 6. Frequency response for microtremor measured using strain gauge at 2.5 cm location with water level of 25 cm

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Fig. 7. Frequency response of strain gauge for water level of 25 cm

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Fig. 8. Frequency response of strain gauge for water level of 40 cm

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Fig. 9. Frequency response of strain gauge for water level of 55 cm

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Fig. 10. Frequency response of strain gauge for water level of 70 cm

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Fig. 11. Normalized acceleration signals according to different water levels

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Fig. 12. Frequency response for microtremor measured using accelerometer

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Fig. 13. Frequency response of accelerometer after hammer impacting

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Fig. 14. Maximum frequency according to water level

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