• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2011.04a
• /
• pp.157-160
• /
• 2011

본 연구에서는 광섬유 센서 기반 스마트 모니터링 시스템이 지중 열전도도 측정에도 효율적으로 적용될 수 있는지를 분석하였다. 이를 위해 광섬유 온도센서를 이용하여 지반의 열전도도를 측정할 수 있는 열응답 시험기가 개발되었다. 개발된 열응답 시험기는 기존의 RTD(Resistance Temperature Detector) 온도 센서 외에 광섬유 센서의 한 종류인 FBG(Fiber Bragg Grating) 센서도 실시간적으로 측정할 수 있는 시스템으로 구성되어 있다. 개발된 장비의 적용성 검증을 위하여 주문진 표준사를 이용하여 모형토조 내에 일정한 간극비에 맞추어 시료가 조성되었으며 지중열교환기는 U자형 파이프가 사용되었다. 20시간동안 열응답 시험을 통하여 광섬유 센서와 RTD 센서를 동시에 이용하여 온도값을 측정하여 표준사의 열전도도 값을 산출하였다. 그 결과 모형실험을 통한 열전도도 값은 탐침법을 통해 얻어진 열전도도 값과 선형 열원 모델(line source model) 해석해와 거의 유사하게 나타났으며 광섬유 센서와 RTD 센서와의 온도차는 0.1~0.3$^{\circ}$로써 유사한 값을 나타내었다. 따라서 본 연구에서 개발된 광섬유 기반 열응답 시험기는 지반의 열전도도를 측정하는데 효과적으로 사용될 수 있음을 알 수 있었으며 향후 지열시스템 가동에 따른 지중열 교환기의 손상도 평가 및 경보시스템 개발을 위해 지중열교환기의 거동을 실시간으로 모니터링 하는데 있어서도 효과적으로 사용될 수 있을 것으로 생각된다.

• Magazine of the Korea Institute for Structural Maintenance and Inspection
• /
• v.18 no.2
• /
• pp.10-16
• /
• 2014

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.39 no.1
• /
• pp.37-43
• /
• 2015

Structural health monitoring (SHM) techniques based on the use of active-sensing piezoelectric (PZT) materials have received considerable attention. The validation of the PZT functionality during SHM operation is critical to successfully implementing a reliable SHM system. In this study, we investigated several parameters that affect the admittance-based sensor diagnostic process. We experimentally identified the temperature dependency of the active-sensor diagnostic process. We found that the admittance-based sensor diagnostic process can differentiate the adhesion conditions of bonding materials that are used to install a PZT on a structure, which is important when designing a sensor diagnostic process for an SHM system.

• Journal of the Korean Society for Precision Engineering
• /
• v.29 no.8
• /
• pp.887-895
• /
• 2012

Lamb waves have received a great attention in the structural health monitoring (SHM) societies because they can propagate over relatively large distances in wave guides such as thin plates and shells. The time-of-flights of Lamb waves can be used to detect damages in a wave guide. However, due to the inherent dispersive and multi-mode characteristics of Lamb waves, one must decompose the Lamb wave modes into the symmetric and anti-symmetric modes for SHM applications. Thus, this paper proposes a decomposition method for the two-mode Lamb waves based on two rules: the group velocity ratio rule and the mode amplitude ratio rule. The group velocity ratio rule means that the ratio of the group velocities of fundamental symmetric and anti-symmetric modes is constant, while the mode amplitude ratio rule means that the magnitude of the fundamental symmetric modes of all measured response signals should be always larger than those of the anti-symmetric mode once the input signal is applied so that the magnitude of fundamental symmetric mode of excited Lamb-wave is larger than that of anti-symmetric mode, and vice versa. The proposed method is verified through the experiments ducted for an aluminum plate specimen.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.32 no.7
• /
• pp.51-59
• /
• 2004

An experimental procedure to identify failure modes of impact damage using sensor signals and to analyze their general features is examined. A series of low-velocity impact tests from low energy to damage-induced high energy were performed on the instrumented drop weight impact tester to monitor the stress wave signals due to failure modes such as matrix cracking, delamination, and fiber breakage. The wavelet transform(WT) and Short Time Fourier Transform(STFT) are used to decompose the piezoelectric sensor signals in this study. The extent of the damage in each case was examined by means of a conventional ultrasonic C-scan. The PVDF sensor signals are shown to carry important information regarding the nature of the impact process that can be extracted from the careful signal processing and analysis.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.16 no.1
• /
• pp.99-109
• /
• 2012

This study aimed to develop a Structural Health Monitoring System for steel beams in the manner of suggesting and verifying a theoretical formula for displacement estimation using strain gauges, and estimating the loading points and magnitude. According to the results of this study, it was found that when a load of 160kN (56% of the yield load) was applied, the error rate of the deflection obtained with a strain gauge at the point of maximum deflection compared to the deflection measured with a displacement meter was within 2%, and that the estimates of the magnitude and points of load application also showed the error rate of not more than 1%. This suggests that the displacement and load of steel beams can be measured with strain gauges and further, it will enable more cost-effective sensor designing without displacement meter or load cell. The Structural Health Monitoring System program implemented in Lab VIEW gave graded warnings whenever the measured data exceeds the specified range (strength limit state, serviceability limit state, yield strain), and both the serviceability limit state and strength limit state could be simultaneously monitored with strain gauge alone.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2010.04a
• /
• pp.683-686
• /
• 2010

본 논문은 최근 이슈가 되고 있는 대형 건축/토목구조물에 대한 동적계측, 시스템판별, 모델향상 등을 통한 건전도 평가기법에 대하여, 현재까지 개발된 혹은 개발되고 있는 기술사항 들을 소개한다. 특히, 가속도계를 사용하여 의도하는 진동기록을 획득하기 위한 합리적인 Hardware Chain 구성, 이로부터 신뢰성 있는 동적 구조성능치를 추출하기 위한 다양한 고급 모달해석기법 및 보다 자세한 구조정보 획득 및 손상감지 등을 위하여 실험치와 유한요소 해석치를 일치시키는 모델향상기법에 대하여 기술하였다. 또한 이러한 기술들을 실제 구조물인 고층건물 및 비닐하우스 아치구조에 적용하였으며, 이러한 경험에 근거하여 현 모니터링 기술의 문제점 및 향후 개선방향 등을 토의하였다.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.24 no.1
• /
• pp.107-117
• /
• 2011

In this study, the effect of temperature-induced uncertainty to damage monitoring using acceleration-impedance response features is analyzed for presterssed concrete(PSC) girder bridges. Firstly, a damage monitoring algorithm using global and local vibration features is designed. As global and local features, acceleration and electro-mechanical impedance features are selected respectively. Secondly, the temperature effect on the acceleration and impedance features for a lab-scaled PSC girder is experimentally analyzed. From the experimental results, compensation models for temperature-acceleration features and temperature-impedance features are estimated. Finally, the feasibility of the acceleration-impedance-based damage monitoring technique using the compensation model is evaluated in the PSC girder for which a set of prestress-loss and flexural stiffness loss cases were dynamically tested.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.22 no.3
• /
• pp.69-74
• /
• 2018

Fiber-Reinforced Cementitious Composites (FRCCs) have electrical conductivity by inserting reinforced conductive fibers into a cementitious matrix. Such characteristic allows us to utilize FRCCs for crack monitoring of a structure by measuring electrical responses without sensor installation. However, the electrical responses are often sensitively altered by temperature variation as well as crack initiation. The temperature variation may disturb crack detection on the measured electrical responses. Moreover, as sensing probes for measuring electrical reponses increase, undesired contact noises are often augmented. In this paper, a self-sensing impedance circuit is specially designed for reducing the number of sensing probes. The crack initiation and temperature variation effects on the self-sensing impedance responses of FRCCs are experimentally investigated using the self-sensing impedance circuit. The experiment results reveal that the electrical impedance response are more sensitively changed due to temperature variation than crack initiation.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.14 no.6
• /
• pp.171-178
• /
• 2010

Pipeline structure is one of core underground infrastructure which transports primary sources. Since the almost pipeline structures are placed underground and connected each other complexly, it is difficult to monitor their structural health condition continuously. In order to overcome this limitation of recent monitoring technique, recently, a Ubiquitous Sensor Network (USN) system based on on-line and real-time monitoring system is being developed by the authors' research group. In this study, real-time pipeline health monitoring (PHM) methodology is presented based on electromechanical impedance methods using USN. Two types of damages including loosened bolts and notches are artificially inflicted on the pipeline structures, PZT and MFC sensors that have piezoelectric characteristics are employed to detect these damages. For objective evaluation of pipeline conditions, Damage metric such as Root Mean Square Deviation (RMSD) value was computed from the impedance signals to quantify the level of the damage. Optimal threshold levels for decision making are estimated by generalized extreme value(GEV) based statistical method. Throughout a series of experimental studies, it was reviewed the effectiveness and robustness of proposed PHM system.