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2021 Vol.37, Issue 11 Preview Page
Natural Frequency Measurement for Scour Damage Assessment of Caisson Pier

교량 우물통 기초의 세굴피해 평가를 위한 고유진동수 측정

Quang-Thien-Buu Nguyen1
,
Seok-Jun Ko2
,
Gyungja Jung3
,
Ju-Hyung Lee4
,
Min-Taek Yoo5
,
Sung-Ryul Kim6*
Nguyen Quang-Thien-Buu1
,
고 석준2
,
정 경자3
,
이 주형4
,
유 민택5
,
김 성렬6*
1Ph.D.Candidate, Dept. of Civil & Environmental Eng., Seoul National Univ.
2Graduate Student, Dept. of Civil & Environmental Eng., Seoul National Univ.
3Member, Principal Researcher, Korea Expressway Corporation Research Institute
4Member, Research Fellow, Dept. of Geotechnical Engineering Research, KICT
5Member, Senior Researcher, Korea Railroad Research Institute
6Member, Associate Prof., Dept. of Civil & Environmental Eng., Seoul National Univ.
1비회원, 서울대학교 건설환경공학부 박사과정
2비회원, 서울대학교 건설환경공학부 석사과정
3정회원, 한국도로공사 수석연구원
4정회원, 한국건설기술연구원 지반연구본부 연구위원
5정회원, 한국철도기술연구원 선임연구원
6정회원, 서울대학교 건설환경공학부 부교수
*Corresponding Author
30 November 2021. pp. 51-60
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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.

Keywords
Caisson foundation
Impact vibration test
Natural frequency
Scour

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.

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Information
  • Publisher :The Korean Geotechnical Society
  • Publisher(Ko) :한국지반공학회
  • Journal Title :Journal of the Korean Geotechnical Society
  • Journal Title(Ko) :한국지반공학회 논문집
  • Volume : 37
  • No :11
  • Pages :51-60
  • Received Date : 2021-10-13
  • Revised Date : 2021-11-05
  • Accepted Date : 2021-11-05
  • DOI :https://doi.org/10.7843/kgs.2021.37.11.51
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