• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.4
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• pp.417-423
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• 2015

In this study, Magnetic Flux Leakage(MFL)-based inspection system was applied to detect the local fault of wire rope. To verify the feasibility of the proposed damage detection technique, an 4-channel MFL sensor head prototype was designed and fabricated. A wire rope with several types of cross-sectional damages were fabricated and scanned by the MFL sensor head to measure the magnetic flux density of the wire rope specimen. To interpret the condition of the wire rope, magnetic flux signals were used to determine the locations of the flaws. To improve the resolution of signal, the instantaneous variation value of magnetic flux was utilized. Measured signals from the damaged specimen were compared with thresholds set for objective decision making. Finally, the results were compared with information on actual inflicted damages to confirm the accuracy and effectiveness of the proposed cable monitoring method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.4
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• pp.287-292
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• 2012

In this study, Multi-Channel Magnetic Flux Leakage(MFL) sensor - based inspection system was applied to monitor the condition of cables. This inspection system measures magnetic flux to detect the local faults(LF) of steel cable. To verify the feasibility of the proposed damage detection technique, an 8-channel MFL sensor head prototype was designed and fabricated. A steel cable bunch specimen with several types of damage was fabricated and scanned by the MFL sensor head to measure the magnetic flux density of the specimen. To interpret the condition of the steel cable, magnetic flux signals were used to determine the locations of the flaws and the level of damage. Measured signals from the damaged specimen were compared with thresholds set for objective decision making. In addition, the magnetic flux density values measured from every channel were summed to focus on the detection of axial location. And, sum of flux density were displayed with threshold. Finally, the results were compared with information on actual inflicted damages to confirm the accuracy and effectiveness of the proposed cable monitoring method.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.6 s.52
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• pp.57-65
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• 2006

This paper presents hybrid structural damage monitoring system which performs both global damage assessment of structure and damage detection of local structural joints. Hybrid damage monitoring system is composed of vibration-based technique and electro/mechanic impedance technique. Vibration-based technique detects global characteristic change ot structure using modal characteristic change of structure, and electro/mechanical impedance technique detects damage existence of local structural joints using impedance change of PZT sensor. For the verification of the proposed hybrid monitoring system, a series of damage scenarios are designed to loosened bolts situations of the structural joints, and acceleration response and impedance response signatures are measured. The proposed hybrid monitoring system is implemented to monitor global damage-state and local damages in structural joints.

• Journal of Korean Society of Disaster and Security
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• v.11 no.2
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• pp.53-60
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• 2018

To diagnosis the local damages of the steel plates, magnetic flux leakage (MFL) method that is known as a adaptable non-destructive evaluation (NDE) method for continuum ferromagnetic members was applied in this study. To analysis the sensitivity according to thickness of steel plate in MFL method based damage diagnosis, several steel plate specimens that have different thickness were prepared and three depths of artificial damage were formed to the each specimens. To measured the MFL signals, a MFL sensor head that have a constant magnetization intensity were fabricated using a hall sensor and a magnetization yoke using permanent magnets. The magnetic flux signals obtained by using MFL sensor head were improved through a series of signal processing methods. The capability of local damage detection was verified from the measured MFL signals from each damage points. And, the peak to peak values (P-P value) extracted from the detected MFL signals from each thickness specimen were compared each other to analysis the MFL based local damage detection sensitivity according to the thickness of steel plate.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.4
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• pp.360-366
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• 2011

The Elasto-magnetic sensor is applied to detect the local cross-sectional loss of steel cables in this study while it was originally developed for measuring the tensile force in the previous works. To verify the feasibility of the proposed damage detection technique, steel bars which have 4-different diameters were fabricated and the output voltage value was measured at each diameter by the E/M sensor. Optimal input voltage and working point are chosen so that the linearity and resolution of results can ensure through repeated experiments, and then the E/M sensor was measured the output voltage values at the damage points of steel bar specimen that was applied the 4 types of damage condition based on the selected optimal experimental condition. This proposed approach can be an effective tool for steel cable health monitoring.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.106-109
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• 2009

본 논문에서는 교량의 상태감시 테스트베드 구축을 위한 한-미 국제공동연구의 현황 및 활동 내용들을 논하였다. 이 국제공동연구는 최첨단 센서와 구조건전도 모니터링 방법의 유용성 및 통합화하는데 그 목적을 두고 있다. 테스트베드 구축을 위해 가속도계과 동적 FBG 센서, 압전 센서 등과 같은 스마트 센서를 사용하였으며, 무선 데이터수집 시스템이 도입되었다. 교량 모니터링 기법으로는 압전 센서 및 EM센서로부터 취합된 데이터를 이용하여 국부손상검색을 수행하였으며, 가속도계, 동적 FBG센서 및 이미지 프로세싱을 이용하여 진동기반 전역손상검색을 수행하였다. 테스트베드 교량으로는 PC박스 거더교, 강상자형교, 강판형교, 사장교의 4가지 형식의 교량이 사용되었다. 테스트베드 교량에 최신 이동통신 인터넷 연결기술을 이용하여 교량에 설치된 센서로부터 취합된 데이터와 모니터링 시스템으로부터 교량의 상태를 실시간 감시할 수 있는 네트워크 시스템을 구축하였다. 이러한 원거리 이동통신시스템을 통하여 구조물의 건전성 평가결과를 실시간으로 전송 및 분석할 수 있도록 하였다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.4
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• pp.185-192
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• 2011

A CFRP (Carbon Fiber-Reinforced Plastic) strengthening method being widely used to increase the load-carrying capacity of structures is very suitable for existing bridge structures. However, not only flexure and shear failures but also debonding failure might be additionally occured in reinforced concrete(RC) beams strengthened with the CFRP plates. The CFRP debonding failure would cause a brittle fracture of the beam. Therefore, health monitoring for the CFRP bonding condition is strongly required. In this study, a feasibility of the impedance-based damage detection method using PZT sensors was investigated through a series of experimental studies for realtime structural health monitoring(SHM) for the CFRP laminated concrete structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.5
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• pp.72-78
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• 2010

A CFRP (Carbon Fiber-Reinforced Plastic) strengthening method is being very widely used to increase the load-carrying capacity of host structures, especially for bridges. However, not only flexure and shear failures but debonding failure also might occur in CFRP strengthened concrete structures. The CFRP debonding failure would cause a collapse accident of the host structure. Therefore, real-time health monitoring about the CFRP bonding condition is strongly required. In this study, a feasibility of the impedance-based damage detection method using PZT sensors is investigated through a series of experimental study monitoring both concrete cracks and CFRP debonding defects.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.21-26
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• 2007

This paper presents an impedance-based structural health monitoring (SHM) technique considering temperature effects. The temperature variation results in a significant impedance variation, particularly both horizontal and vertical shifts in the frequency domain, which may lead to erroneous diagnostic results of real structures. A new damage detection strategy has been proposed based on the correlation coefficient (CC) between the reference impedance data and a concurrent impedance data with an effective frequency shift which is defined as the shift causing the maximum correlation. The proposed technique was applied to a lab-sized steel truss bridge member under the temperature varying environment. From an experimental study, it has been demonstrated that a narrow cut inflicted artificially to the steel structure was successfully detected using the proposed SHM strategy.