Journal of the Korean Geotechnical Society (한국지반공학회논문집)

Korean Geotechnical Society (한국지반공학회)
권호 표지
DOI QR코드

DOI QR Code

Natural Frequency Measurement for Scour Damage Assessment of Caisson Pier

교량 우물통 기초의 세굴피해 평가를 위한 고유진동수 측정

  • ;
  • 고석준 (서울대학교 건설환경공학부) ;
  • 정경자 (한국도로공사) ;
  • 이주형 (한국건설기술연구원 지반연구본부) ;
  • 유민택 (한국철도기술연구원) ;
  • 김성렬 (서울대학교 건설환경공학부)
  • Received : 2021.10.13
  • Accepted : 2021.11.05
  • Published : 2021.11.30
Download PDF
⟨ Previous Next ⟩

Abstract

River scour erodes the soil around the pier, reducing the lateral bearing capacity of the pier and lowering the stability of the structure. In this study, in order to examine the effect of scouring on the stability of the structure, an experiment was performed to measure the natural frequency of the pier according to the excavation of the surrounding ground. Impact vibration test was conducted on the pier with the caisson foundation of the Mangyeonggang Bridge, which is scheduled to be demolished. Accelerometers were attached to the top, center, and bottom of the pier and the acceleration responses were measured by hitting those three points. The experimental results showed that the top hit showed consistent and reasonable results of the acceleration responses according to the hitting position. The measured accelerations were converted to the frequency domain through Fast Fourier Transform (FFT), and then the natural frequency was determined. In addition, to analyze the scour effect on the natural frequency of the pier, the ground around the pier was excavated and the natural frequency change was analyzed. As a result, the natural frequency showed the decreasing tendency according to the excavation depth, but the decrease was small due to the large stiffness of the caisson foundation.

하천의 세굴은 교각 주변의 흙을 침식시켜 교각의 횡방향 지지력을 저감시키고 구조물의 건전도를 저하시키게 된다. 본 연구에서는 세굴이 구조물의 건전도에 미치는 영향을 살펴보고자 주변지반의 굴착에 따른 교각의 고유진동수 측정실험을 수행하였다. 폐교예정인 만경강교의 우물통기초 교각에서 충격진동시험을 수행하였다. 교각의 상단, 중앙, 하단에 가속도계를 부착하고 세 지점을 타격하여 가속도를 계측하였다. 실험 결과, 타격위치에 따른 가속도 측정값 중 상단타격이 일관되고 합리적인 가속도 결과를 보여주었다. 계측된 가속도는 고속 푸리에 변환(FFT)을 통하여 주파수 영역으로 변환되었고, 이를 이용하여 고유진동수를 측정하였다. 또한, 세굴이 교각의 고유진동수 변화에 미치는 영향을 분석하기 위하여 교각 주변 지반을 굴착하면서 고유진동수의 변화를 측정하였다. 그 결과, 굴착 깊이에 따라 고유 진동수가 감소하는 경향을 보여주었지만, 우물통 기초형식이 큰 강성을 가지고 있어 그 감소폭은 작은 것으로 나타났다.

Keywords

Acknowledgement

본 연구는 한국도로공사 도로교통연구원의 "교량기초 점검 및 평가 방안 개발" 과제 및 국토교통부/국토교통과학기술진흥원(21SCIP-C155167-03: MT21027)의 지원으로 수행되었으며, 이에 깊은 감사를 드립니다.

References

  1. Ghatak, A. (2005), Optics (3rd ed.), Tata McGraw-Hill, New Delhi.
  2. Ju, S.H. (2013), "Determination of Scoured Bridge Natural Frequency with Soil-structure Interaction", Soil Dynamics and Earthquake Engineering, 55, pp.247-254. https://doi.org/10.1016/j.soildyn.2013.09.015
  3. Jung, H.S., Lee, M.J., Yoo, M.T., and Lee, I.W. (2020), "Response Dominant Frequency Analysis for Scour Safety Evaluation of Railroad Piers", Journal of the Korean Geotechnical Society, Vol.36, No. 11, pp.88-95.
  4. Kien, P.H. (2017), "Application of Impact Vibration Test Method for Bridge Substructure Evaluation", The 6th International Conference of Euro Asia Civil Engineering Forum, Seoul, Korea.
  5. Kim, Y.J. and Yu, D.W. (2002), "Lessons and Analysis of Event in Domestic Bridge Failures", Journal of Korean Society of Civil Engineers, Vol.50, No.8, pp.34-40.
  6. Kim, B.I., Yoon, K.Y., and Lee, S.H. (2005), "Field Investigation of Scour-protection Methods for Bridges in Small Size Streams of Central Region of Korea", Journal of Korean Society of Hazard Mitigation, Vol.5, No.1, pp.45-53.
  7. Kim, Y.D., Lee, J.S., Lee, I.W., and Yu, J.D. (2021), "Natural Frequencies of Model Piers under Different Ground Support Conditions", Journal of Korean Society of Hazard Mitigation, Vol.21, No.1, pp.239-249.
  8. Korea Infrastructure Safety Corp (2003), Daegu Line Josancheon Bridge and 23 Other Precise Safety Diagnosis Reports.
  9. Korea railroad research institute (2017), Korean Railway in Statistics.
  10. Korea railroad research institute (2018), Field Condition Evaluation Verification Test Service Report for Securing Reliability of Pier Test Method.
  11. Korea railroad research institute (2018), On-site Railway Bridge Impact Vibration Test and Natural Frequency Analysis Report.
  12. Korea railroad research institute (2019), Development of collapse diagnosis technique using loss-information building model based on CPM (Cyber Physics Model), Final Report of Major Projects 2019.
  13. Kwak, K.S., Park, J.H., Chung, M.K., and Woo, H.S. (2006), "Bridge Scour Prioritization and Management System (I) - System Development", Journal of The Korean Society of Civil Engineers, 26(2B), pp.187-195.
  14. Lee, M.J., Yoo, M.T., Kim, K.H., and Lee, I.W. (2019), "Establishment of Testing Method for Abutment Scour Stability by Real-scale Model Test", Journal of the Korean Geotechnical Society, Vol.35, No.7, pp.5-14. https://doi.org/10.7843/KGS.2019.35.7.5
  15. Ministry of Land, Infrastructure, Transport and Tourism (2007), Railroad structure maintenance standard, building explanation (structure part), Foundation Structure, Combined Earth Pressure Structure, Tokyo.
  16. Park, J.H., Kwak, K.S., Yoon, H.S., Lee, J.H., and Chung, M.K. (2005), "Evaluation of Bridge Scour Vulnerability for Bridges Near Kangneung Area", Journal of Korean Society of Civil Engineers, pp.4276-4279.
  17. Prendergast, L.J., Hester, D., Gavin, K., and O'Sullivan, J.J. (2013), "An Investigation of the Changes in the Natural Frequency of a Pile Affected by Scour", Journal of Sound and Vibration, 332, pp.6685-6702. https://doi.org/10.1016/j.jsv.2013.08.020
  18. Prendergast, L.J., Gavin, K., and Doherty, P. (2015), "An Investigation into the Effect of Scour on the Natural Frequency of an Offshore Wind Turbine", Journal of Ocean Engineering and Science, 101, pp.1-11. https://doi.org/10.1016/j.oceaneng.2015.04.017
  19. Railway Technical Research Institute (2000), Design Standard for Railway Earth Structure (in japanese), Maruzen.
  20. Samizo, M., Watanabe, S., Fuchiwaki, A., and Sugiyama, T. (2007), "Evaluation of the Structural Integrity of Bridge pier Foundations Using Microtremors in Flood Conditions", Quarterly Report of RTRI, Vol.48, No.3, pp.153-157. https://doi.org/10.2219/rtriqr.48.153
  21. Shirhole, A.M. and Holt, R.C. (1991), "Planning for a Comprehensive Bridge Safety Assurance Program", Transportation Research Record, 1290, pp.137-142.
  22. Smith, D.W. (1976), "Bridges failures", Proceedings of the Institute of Civil Engineers, Vol.60, No.1, pp.367-382. https://doi.org/10.1680/iicep.1976.3389
  23. Yeo, W.K. and Kang, J.G. (1999), "Field Investigation of Bridge Scours in Small and Medium Streams(2)", Journal of Korea Water Resources Association, Vol.32, No.1, pp.41-47.