• Journal of Korean Society of Steel Construction
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• v.22 no.1
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• pp.21-31
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• 2010

In this study, a technique that uses wireless impedance sensor nodes is proposed to monitor tensile force of structural cable. To achieve this goal, the following approaches were implemented. First, a wireless impedance sensor node was designed for automated and cost-efficient prestress-loss monitoring. Second, an impedance-based algorithm was embedded in the wireless impedance sensor node for autonomous structural health monitoring of structural cables. Third, a tensile force monitoring technique that uses an interface plate for structural cables was proposed to overcome the limitations of the wireless impedance sensor node such as its narrow-band measurable frequency ranges. Finally, the applicability of the wireless impedance sensor node and the technique that uses the interface washer were evaluated in a lab-scaled prestressed concrete (PSC) girder model with internal and external tendons for which several prestress-loss scenarios were experimentally monitored with the wireless impedance sensor nodes.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.1-7
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• 2018

Suspension bridge cables made of high strength steel wires require periodical maintenance in accordance with the axial force of cable-band bolts, since the bolts in suspension bridges can undergo tension decrease due to creep of cable wires, bolt relaxation, load fluctuation, and cable re-arrangement, etc. Consequently, this study is aimed at investigating and subsequently evaluating the critical factors with respect to the bolt tension-decrease phenomenon in SR suspension bridge in Korea, based on field monitoring, theoretical studies, and field record management works. From the observation, it is interesting to note that the decrease in the bolt tension force is typically accompanied by plastic deformation of the zinc plating layers in the cable wires. In addition, a framework corresponding to generic methodologies to characterize the deformation in terms of the bolt tension-decrease and long-term history management has been developed in this exploratory study.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.172-181
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• 2023

In this study, real-time damage evaluation of cable-stayed bridges was conducted for cable damage. ICP type acceleration sensors were used for real-time damage assessment of cable-stayed bridges, and Kinetic Energy Optimization Techniques (KEOT) were used to select the optimal conditions for the location and quantity of the sensors. When a structure vibrates by an external force, KEOT measures the value of the maximum deformation energy to determine the optimal measurement position and the quantity of sensors. The damage conditions in this study were limited to cable breakage, and cable damage was caused by dividing the cable-stayed bridge into four sections. Through FE structural analysis, a virtual model similar to the actual model was created in the real-time damage evaluation method of cable. After applying random oscillation waves to the generated virtual model and model structure, cable damage to the model structure was caused. The two data were compared by defining the response output from the virtual model as a corruption-free response and the response measured from the real model as a corruption-free data. The degree of damage was evaluated by applying the data of the damaged cable-stayed bridge to the Improved Mahalanobis Distance (IMD) theory from the data of the intact cable-stayed bridge. As a result of evaluating damage with IMD theory, it was identified as a useful damage evaluation technology that can properly find damage by section in real time and apply it to real-time monitoring.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1002-1006
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• 2006

Temperature monitoring techniques per depth have been recognized as important information in the reservoir environmental issues. However, old measurement method by single temperature sensor and cable type has demerits not only for its limited measuring location but for its inconvenience of users. In this study, multi-channel temperature monitoring system was introduced and executed experiment for actual application feasibility evaluation. Both type of new techniques such as multi-channel addressable built-in temperature sensor and fiber optic multi sensor were tested in Daechung and Imha reservoir. As a result, it was proved that these kinds of temperature monitoring skills had very good performance and availability for a output of spatial, simultaneous thermal distribution focused on the user's convenience. And these measuring method and thermal data will be useful for providing basic information in a water resources investigation like reservoir stratification and environmental problems.

• Smart Structures and Systems
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• v.11 no.5
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• pp.533-553
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• 2013

In this paper, system identification of a cable-stayed bridge in Korea, the Hwamyung Bridge, is performed using vibration responses measured by a wireless sensor system. First, an acceleration based-wireless sensor system is employed for the structural health monitoring of the bridge, and wireless sensor nodes are deployed on a deck, a pylon and several selected cables. Second, modal parameters of the bridge are obtained both from measured vibration responses and finite element (FE) analysis. Frequency domain decomposition and stochastic subspace identification methods are used to obtain the modal parameters from the measured vibration responses. The FE model of the bridge is established using commercial FE software package. Third, structural properties of the bridge are updated using a modal sensitivity-based method. The updating work improves the accuracy of the FE model so that structural behaviors of the bridge can be represented better using the updated FE model. Finally, cable forces of the selected cables are also identified and compared with both design and lift-off test values.

• Smart Structures and Systems
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• v.15 no.2
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• pp.425-445
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• 2015

Parametric identification of structures is one of the important aspects of structural health monitoring. Most of the techniques available in the literature have been proved to be effective for structures with small degree of freedoms. However, the problem becomes challenging when the structure system is large, such as bridge structures. Therefore, it is highly desirable to develop parametric identification methods that are applicable to complex structures. In this paper, the LSE based techniques will be combined with the substructure approach for identifying the parameters of a cable-stayed bridge with large degree of freedoms. Numerical analysis has been carried out for substructures extracted from the 2-dimentional (2D) finite element model of a cable-stayed bridge. Only vertical white noise excitations are applied to the structure, and two different cases are considered where the structural damping is not included or included. Simulation results demonstrate that the proposed approach is capable of identifying the structural parameters with high accuracy without measurement noises.

• Smart Structures and Systems
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• v.17 no.3
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• pp.491-522
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• 2016

A benchmark problem for modal identification of a cable-stayed bridge was proposed by a research team at Hong Kong Polytechnic University. By taking an instrumented cable-stayed bridge as a test bed, nineteen sets of vibration records with known/unknown excitations were provided to invited researchers. In this paper, the vibration responses of the bridge under a series of excitation conditions are examined to estimate the wind and traffic-induced variations of its dynamic characteristics. Firstly, two output-only experimental modal identification methods are selected. Secondly, the bridge and its monitoring system are described and the nineteen sets of vibration records are analyzed in time-domain and frequency-domain. Excitations sources of blind datasets are predicted based on the analysis of excitation conditions of known datasets. Thirdly, modal parameters are extracted by using the two selected output-only modal identification methods. The identified modal parameters are examined with respect to at least two different conditions such as traffic- and typhoon-induced loadings. Finally, the typhoon-induced effects on dynamic characteristics of the bridge are estimated by analyzing the relationship between the wind velocity and the modal parameters.

• Proceedings of the KIEE Conference
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• 2006.07e
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• pp.15-16
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• 2006

배전선로에 전력을 공급하는 방식은 일반적으로 22.9kV급 XLPE 케이블에 의한 전력공급이 주를 이루어 왔다. 한편으로 대규모 전력을 소비하는 공장 및 고층 빌딩의 전력 공급에 있어서는 일반적으로 각각 부하로의 많은 회선수의 케이블 포설을 요하는 전력케이블 보다는, 한 선로로 보다 많은 대전류를 수송하면서 부하 가까이에서 필요한 전류를 간편하게 분기해 공급받는 부스덕트 시스템이 시공 및 배전선로 관리의 간편성에 의해 점차 용도가 늘어나고 있다. 부스닥트 시스템의 대부분은 일단 시설물이 건축될 때 건축물의 상부 공간 또는 설비가 위치한 하부 바닥 구간을 통해 설치된 이후, 기타 배관, 가스관 등의 추가적인 건축 구조물과 함께 설치되어 이후 선로의 보수 진단 등이 대부분 어렵게 되어진다. 본 논문에서 소개하는 부스덕트의 온도감시 시스템은 아무리 복잡하고 협소한 설치 환경이라도 특수한 포설 공법에 의해 광화이버를 포설하고, 이를 활용하여 실시간으로 부스덕트 선로의 표면온도와 주변온도를 상시 감시함으로써, 효율적인 부스덕트 선로의 활용뿐만 아니라 과열에 의한 절연사고를 미연 방지하는 운전신뢰성과 안정성을 높이는 것이 가능하게 되었다.

• Structural Monitoring and Maintenance
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• v.5 no.4
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• pp.489-506
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• 2018

This paper reported test of full-scale cables attached with four types of dampers: viscous damper, passive Magneto-Rheological (MR) damper, friction damper and High Damping Rubber (HDR) damper. The logarithmic decrements of the cable with attached dampers were calculated from free vibration time history. The efficiency ratios of the mean damping ratios of the tested four dampers to theoretical maximum damping ratio were derived, which was very important for practical damper design and parameter optimization. Non-ideal factors affecting damper performance were discussed based on the test results. The effects of concentrated mass and negative stiffness were discussed in detail and compared theoretically. Approximate formulations were derived and verified using numerical solutions. The critical values for non-dimensional concentrated mass coefficient and negative stiffness were identified. Efficiency ratios were approximately 0.6, 0.6, and 0.3 for the viscous damper, passive MR damper and HDR damper, respectively. The efficiency ratio for the friction damper was between 0-1.0. The effects of concentrated mass and negative stiffness on cable damping were positive as both could increase damping ratio; the concentrated mass was more effective than negative stiffness for higher vibration modes.

• Journal of Sensor Science and Technology
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• v.32 no.4
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• pp.219-222
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• 2023

Partial discharges (PD) have long been recognized as a major contributing factor to catastrophic failures in high-power equipment. As the demand for high voltage direct current (HVDC) facilities continues to rise, the significance of on-line and real-time monitoring of PD becomes increasingly prominent. In this study, we have designed, fabricated, and characterized a highly sensitive and cost-effective PD sensor comprising a pair of copper electrodes with different arc lengths. The key advantage of our sensor is its non-invasive nature, as it can be installed at any location along the entire power cable without requiring structural modifications. In contrast, conventional PD sensors are typically limited to installation at cable terminals or insulation joint boxes, often necessitating invasive alterations. Our PD sensor demonstrates exceptional accuracy in estimating PD location, with a success rate exceeding 95% in the straight sections of the power cable and surpassing 89% in curved sections. These remarkable characteristics indicate its high potential for realtime and on-line detection of PD.