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박종칠,박찬민,김병화,이일근,조병완 한국지진공학회 2006 한국지진공학회논문집 Vol.10 No.6
본 논문에서는 구조건전성모니터링(SHM)시스템이 설치된 케이블교량을 대상으로 장기적인 동적거동 특성을 분석하였다. 3차원 유한요소모델을 사용한 모드해석을 통해 모드변수를 추출하였다. 이를 교량에서 측정된 상시진동신호에 대해 주파수영역에서 분석한 고유진동수와 비교하여 정확한 기저모델이 구축되었음을 알 수 있었다. 지난 5년간의 고유진동수와 온도를 통계분석하여 고유진동수가 온도에 선형 반비례하고 있음을 확인하였고, 이러한 온도효과에 대한 평가를 수행하였다. 또한 상시진동신호를 시간영역에서 TDD기법을 적용하여 모드형상을 추출하였으며, 모드해석 결과와의 비교를 통해 케이블교량에 적용이 가능함을 검증하였다. This paper presents long-term dynamic characteristics of a cable-stayed bridge where installed SHM (Structural Health Monitoring) system. Modal parameters such as natural frequencies and mode shapes are identified by modal analysis using three dimensional finite element model. The developed baseline model has a good correlation with measured natural frequencies identified from field ambient vibrations. By statistical data processing between measured natural frequencies and temperatures, it is demonstrated that the natural frequency is in linearly inverse proportion to the temperature. The estimation of temperature effects against frequency variations is performed. Mode shapes are identified from the TDD (Time Domain Decomposition) technique for ambient vibration measurements. Finally, these results demonstrate that the TDD method can apply to identify modal parameters of a cable-stayed bridge.
박종칠,Park, Jong-Chil 한국구조물진단유지관리공학회 2022 한국구조물진단유지관리공학회 논문집 Vol.26 No.4
The operational modal analysis (OMA) technique, which extracts the modal parameters of a structural system using ambient vibrations, has been actively developed as a field of structural health monitoring of cable-supported bridges. In this paper, the short and long-term modal parameters of a cable-stayed bridge were evaluated using the acceleration data obtained from the two ambient vibration tests (AVTs) and three years of continuous measurements. A total of 27 vertical modes and 1 lateral mode in the range 0.1 ~ 2.5 Hz were extracted from the high-resolution AVTs which were conducted in the 6th and 19th years after its completion. Existing OMA methods such as Peak-Picking (PP), Eigensystem Realization Algorithm with Data Correlation (ERADC), Frequency Domain Decomposition (FDD) and Time Domain Decomposition (TDD) were applied for modal parameters extraction, and it was confirmed that there was no significant difference between the applied methods. From the correlation analysis between long-term natural frequencies and environmental factors, it was confirmed that temperature change is the dominant factor influencing natural frequency fluctuations. It was revealed that the decreased natural frequencies of the bridge were not due to changes in structural performance and integrity, but to the environmental effects caused by the temperature difference between the two AVTs. In addition, when the TDD technique is applied, the accuracy of extracted mode shapes is improved by adding a proposed algorithm that normalizes the sequence so that the autocorrelations at zero lag equal 1.
온도와 변위 데이터를 이용한 사장교의 온도신축거동 평가
박종칠,Park, Jong Chil 대한토목학회 2015 대한토목학회논문집 Vol.35 No.4
케이블교량은 교량길이가 길고 규모가 크기 때문에 온도에 의한 이동량과 형상변화는 일반교량보다 훨씬 크다. 따라서 공용 중 온도영향을 분석, 평가하는 것이 중요하며, 온도영향은 온도변화에 따라 교량 상부구조계가 늘어나거나 줄어드는 온도신축거동을 평가하는 것이 가장 기본이다. 이에 공용 중인 사장교에서 장기간 계측된 온도와 이종 변위 데이터를 활용하여 실제적인 온도신축거동을 평가하고자 하였다. 변위 데이터는 기존 신축변위계와 함께 새롭게 도입된 GNSS(Global Navigation Satellite System) 수신기에서 계측된 데이터를 활용하였다. 먼저 외기온도, 개별온도, 평균온도, 유효온도의 다양한 온도 조합에 대한 신축거동의 상관성을 분석하여 부재의 평균온도나 유효온도를 사용하는 것이 합리적임을 확인하였다. 부재 유효온도와 신축량의 선형회귀분석으로부터 단위온도신축량을 산정하고, 추가적으로 신축길이와 계측 단위온도 신축량의 선형회귀분석으로부터 선팽창계수와 중립점의 위치를 산정할 수 있었다. 이를 이론과 해석 결과와 비교함으로써 케이블교량의 실제 온도신축거동의 건전성을 평가할 수 있는 방안을 제시하였다. Because cable-supported bridges have long spans and large members, their movements and geometrical changes by temperatures tend to be bigger than those of small or medium-sized bridges. Therefore, it is important for maintenance engineers to monitor and assess the effect of temperature on the cable-supported bridges. To evaluate how much the superstructure expands or contracts when subjected to changes in temperature is the first step for the maintenance. Thermal movements of a cable-stayed bridge in service are evaluated by using long-term temperatures and displacements data. Displacements data are obtained from extensometers and newly installed GNSS (Global Navigation Satellite System) receivers on the bridge. Based on the statistical data such as air temperatures, each sensor's temperatures, average temperatures and effective temperatures, correlation analysis between temperatures and displacements has been performed. Average temperatures or effective temperatures are most suitable for the evaluation of thermal movements. From linear regression analysis between effective temperatures and displacements, the variation rate's of displacement to temperature have been calculated. From additional regression analysis between expansion length's and variation rate's of displacement to temperature, the thermal expansion coefficient and neutral point have been estimated. Comparing these parameters with theoretical and analytical results, a practical procedure for evaluating the real thermal behaviors of the cable-supported bridges is proposed.