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

• Journal of Ocean Engineering and Technology
• /
• v.25 no.4
• /
• pp.59-65
• /
• 2011

In structural health monitoring (SHM) using electro-mechanical impedance signatures, it is a critical issue for extremely large structures to extract the best damage diagnosis results, while minimizing unknown environmental effects, including temperature, humidity, and acoustic vibration. If the impedance signatures fluctuate because of these factors, these fluctuations should be eliminated because they might hide the characteristics of the host structural damages. This paper presents a long-term SHM technique under an unknown noisy environment for tidal current power plant structures. The obtained impedance signatures contained significant variations during the measurements, especially in the audio frequency range. To eliminate these variations, a continuous principal component analysis was applied, and the results were compared with the conventional approach using the RMSD (Root Mean Square Deviation) and CC (Cross-correlation Coefficient) damage indices. Finally, it was found that this approach could be effectively used for long-term SHM in noisy environments.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.36 no.3
• /
• pp.211-216
• /
• 2016

In several industrial fields, epoxy resin is widely used as an adhesive for co-curing and manufacturing various structures. Controlling the manufacturing process is required for ensuring robust bonding performance and the stability of the structures. A fiber optic sensor is suitable for the cure monitoring of epoxy resin owing to the thready shape of the sensor. In this paper, a fiber Bragg grating (FBG) sensor was applied for the cure monitoring of epoxy resin. Based on the experimental results, it was demonstrated that the FBG sensor can monitor the status of epoxy resin curing by measuring the strain caused by volume shrinkage and considering the compensation of temperature. In addition, two types of epoxy resin were used for the cure-monitoring; moreover, when compared to each other, it was found that the two types of epoxy had different cure-processes in terms of the change of strain during the curing. Therefore, the study proved that the FBG sensor is very profitable for the cure-monitoring of epoxy resin.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2010.04a
• /
• pp.670-673
• /
• 2010

무기저 손상 진단 기법은 능동센서를 이용하여 과거의 기저자료와 현재 상태에서 취득한 유도파의 정보를 비교하지 않고, 구조물의 현재 상태에서 취득한 신호만을 분석함으로써 구조물의 상태를 진단하는 기법이다. 온도 변화 및 하중 변화 등의 외부 환경의 변화에 민감한 유도파의 특성으로 인하여 기저자료를 이용하는 과거의 방법론은 현실적용성이 떨어질 우려가 있다. 본 무기저 손상 진단 기법은 외부 환경적 영향을 최소화함으로써 구조물의 상태를 효율적으로 진단할 수 있다. 최초, 본 연구진에서 제안하였던 무기저 기법은 두 쌍의 능동센서를 구조물에 양면 대칭으로 배치시켜 능동센서의 극성을 이용한 방법이었다. 하지만 실제 구조물의 양면에 완벽한 대칭성을 유지하며 능동센서를 배치시키는 것은 사실상 불가능하다. 이와 같은 한계점을 극복하기 위해 신개념의 듀얼 능동센서를 활용한 무기저 손상 진단 기법이 제안되었고, 수치해석 및 연구실 환경에서 제한적으로 그 실용성이 검증되었다. 본 논문에서는 무기저 손상 진단 기법의 실 구조물에의 적용성을 폐교량을 대상으로 검토하였다. 특히, 보강재를 포함하는 영역에서 본 기법을 적용함으로써 실제 구조물에 적용 가능성을 검증하였다.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.6A
• /
• pp.399-408
• /
• 2011

Development of smart sensors for structural health monitoring and damage detection has been advanced remarkably in recent years. Nowadays fiber optic sensors, especially fiber Bragg grating (FBG) sensors, have attracted many researchers' interests for their attractive features, such as multiplexing capability, durability, lightweight, electromagnetic interference immunity. In this paper, a damage detection approach of jacket-type offshore structures by principal component analysis (PCA) technique using FBG sensors are presented. An experimental study for a tidal current power plant structure as one of the jacket-type offshore structures was conducted to investigate the feasibility of the proposed method for damage monitoring. It has been found that the PCA technique can efficiently eliminate environmental effects from measured data by FBG sensors, resulting more damage-sensitive features under various environmental variations.

• Information and Communications Magazine
• /
• v.30 no.10
• /
• pp.25-31
• /
• 2013

본고에서는 건설기술과 IT기술이 융합된 건설IT융합기술에서 스마트 빌딩과 관련하여 안전, 건강, 편의, 에너지를 위한 기술들로 분류하여 사례와 함께 서술한다. 고층 빌딩의 안전성을 위한 건축 구조물 건전도 모니터링 기술, 빌딩 실내 또는 지하 주차장에서 쾌적한 공기 환경을 유지하기 위한 스마트 환기제어 시스템 기술, 빌딩 정보의 체계적인 데이터 관리를 위한 빌딩정보모델링 기반의 센서와 영상 인터페이스, 스마트 빌딩 네트워크 관리 시스템에 관하여 소개한다. 또한, 에너지 절감을 위한 빌딩 에너지 관리 시스템에 관하여 냉난방, 조명, 환기설비, 전력모니터링 관련 기술에 대하여 설명한다. 이러한 기술들을 적용한 스마트 빌딩은 유무선통신, 스마트디바이스와 같은 IT기술을 건축공학 및 빌딩자동제어, 설비 기술에 적용하여 빌딩 사용자에게는 안전 및 최적 환경을 제공하고 빌딩 소유주나 관리자에게는 관리비용 절감, 관리 편의, 빌딩가치 상승 등을 제공할 수 있다.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.20 no.2
• /
• pp.166-171
• /
• 2010

Wired monitoring systems have been used for damage detection and dynamic analysis of large structures(bridges, dams, plants, etc.). However, the real-world applications still remain limited, mainly due to time and cost issues inherent to wired systems. In recent years, an increasing number of researchers have adopted WSN(wireless sensor network) technologies to the field of SHM(structural health monitoring). Accurate time synchronization is most critical for the wireless approach to be feasible for SHM purpose, along with sufficient wireless bandwidth and highly precise measuring resolution. To satisfy technical criteria stated above, a wireless vibration monitoring system that uses high-precision MEMS(micro-electro-mechanical system) sensors and A/D convertor is discussed in detail. It was found experimentally that the level of time synchronization fell within $200\;{\mu}sec$.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.29 no.1A
• /
• pp.61-73
• /
• 2009

In this paper, hybrid health monitoring techniques using acceleration-impedance features are newly proposed to detect two damage-type in steel plate-girder bridges, which are girder's stiffness-loss and support perturbation. The hybrid techniques mainly consists of three sequential phases: 1) to alarm the occurrence of damage in global manner, 2) to classify the alarmed damage into subsystems of the structure, and 3) to estimate the classified damage in detail using methods suitable for the subsystems. In the first phase, the global occurrence of damage is alarmed by monitoring changes in acceleration features. In the second phase, the alarmed damage is classified into subsystems by recognizing patterns of impedance features. In the final phase, the location and the extent of damage are estimated by using modal strain energy-based damage index method and root mean square deviation (RMSD) method. The feasibility of the proposed hybrid technique is evaluated on a laboratory-scaled steel plate-girder bridge model for which hybrid acceleration-impedance signatures were measured for several damage scenarios. Also, the effect of temperature on the accuracy of the impedance-based damage monitoring results are experimentally examined from combined scenarios of support damage cases and temperature changes.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.17 no.2
• /
• pp.10-20
• /
• 2013

To evaluate the safety of a beam structure, strains are measured as an indicator of structural states. However, unless strain sensors are installed exactly on where maximum or other representative strains occur, the techniques by which rational assessment through measured strains is accomplished are required. Thus, this study suggests a process to estimate strain distribution on the steel beam from discrete strains measured by sensors. In the presented technique, the targeted beam is regarded to be subjected to unknown loads so that applicability is enhanced. Final strain distribution is given as form of a function after regression analysis. To verify the performance of estimation, a bending test for steel beam on which distributed and concentrated loads simultaneously act is conducted. From the comparison between estimated and directly measured strains in the test, the curve of strain distribution and the strain at arbitrary location could be predicted within maximum relative error 3.32% and maximum absolute error of $2.32{\mu}{\varepsilon}$, respectively. Thus reliable and practical monitoring is expected to apply effectively for the steel beam structure.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.18 no.6
• /
• pp.105-113
• /
• 2014

Most operating civil structures measure response data continuously by various types of sensors and evaluate their health conditions. Measurement control criteria for such civil structures are usually defined in the first operating stage by experts working at a construction or engineering company. However, a few studies have been carried to examine the adequacy of these measurement control criteria based on the actual measured data. The paper introduces a systematic way of resetting the measurement control criteria for the measured monitoring data based on the statistical aspects of the measured data. The proposed statistical approach has been examined with actually measured time-history data from a bridge structure.