• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.3
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• pp.331-343
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• 1999

본 논문에서는 새로이 유도된 진동기초 손상검색방법을 제시하고, 제한적인 모드특성치가 측정된 구조물을 대상으로 이 알고리즘의 적합성과 손상예측의 정확도를 검증하고자 하였다. 먼저, 기존의 Kim과 Stubbs에 의해 발표된 손상발견 알고리즘들을 검토하였으며, 이 알고리즘들의 적용한계와 오류적 가정을 극복할 수 있는 손상검색 알고리즘을 새로이 유도하였다. 다음으로, 손상발생 전후에 소수의 진동모드 특성치가 측정된 2경간 연속보를 대상으로 손상예측실험을 수행하여, 이들 손상검색 알고리즘의 손상예측 정확도를 분석하였다. 기존의 손상검색 알고리즘에 비하여 새로이 유도된 손상검색 알고리즘의 손상예측 정확도가 향상된 것으로 분석되었다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.3 s.73
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• pp.313-322
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• 2006

In the genetic algoricm (GA) based damage detection methods using vibration of structures, the selection of modal properties is important to improve the accuracy of damage detection. The objective of this study is to improve the accuracy of damage detection using natural frequency and modal strain energy, The following approaches are used to achieve the goal. First, modal strain energy is formulated and a new GA-based damage detection technique using natural frequency and modal strain energy is proposed. Next, to verify the efficiency of proposed technique, damage scenarios for free-free beam are designed and vibration modal tests of the target structure are conducted. Finally, the feasibility of the proposed technique is verified in comparison with other GA-based damage detection technique using natural frequency and mode shape.

• 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 Korea institute for structural maintenance and inspection
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• v.10 no.6
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• pp.113-123
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• 2006

As Cable-stayed bridges were constructed to the long span, they have become bigger and had weaknesses to vibration induced by earthquake, wind and vehicle loads. Structural damages induced by these loads affect the characteristic of vibration modes of structure. Damage detection of cable-stayed bridges by using existing safety diagnosis is difficult to detect the characteristic change of overall structural action. Also it requires very much time and cost. So in this study, the investigation of characteristic change of structural action and the detection of structural damages is analyzed by using characteristic properties of vibration mode before and after structural damage.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.1
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• pp.165-174
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• 2010

In this paper, a two-phase structural health monitoring system using acceleration response signatures are presented to firstly alarm the change in structural condition and to secondly detect the changed location for full-scale concrete girder bridges. Firstly, Mihocheon Bridge which is a two-span continuous concrete girder bridge is selected as the target structure. The dynamic response features of Mihocheon Bridge are extracted by forced vibration test using bowling ball. Secondly, the damage alarming occurrence and the damage localization techniques are selected to design two-phase structural health monitoring system for Mihocheon Bridge. As the damage alarming techniques, auto-regressive model using time-domain signatures, correlation coefficient of frequency response function and frequency response ratio assurance criterion are selected. As the damage localization technique, modal strain energy-based damage index method is selected. Finally, the feasibility of two-phase structural health monitoring systems is evaluated from static loading tests using a dump truck.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.1
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• pp.43-58
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• 2002

A methodology to nondestructively locate and estimate size of damage in beam-type structures using a few natural frequencies or a few mode shapes is presented. A damage-localization algorithm to locate damage from changes in natural frequencies and a damage-sizing algorithm to estimate crack-size from natural frequency perturbation are outlined. A damage index algorithm to localize and estimate severity of damage from monitoring changes in mode shapes is outlined. The frequency-based method and the mode-shape-based method are evaluated for several damage scenarios by locating and sizing damage in PS concrete beams lot which a few natural frequencies and mode shapes are generated from finite element models. The result of the analyses indicates that the two methods correctly localize and closely estimate the size of the crack simulated in the test beam.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.3
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• pp.229-237
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• 2007

In this study, an artificial neural network (ANN)-based damage detection algorithm using acceleration signals is developed for real-time alarming locations of damage in beam-type structures. A new ANN-algorithm using output-only acceleration responses is designed tot damage detection in real time. The cross-covariance of two acceleration-signals measured at two different locations is selected as the feature representing the structural condition. Neural networks are trained lot potential loading Patterns and damage scenarios of the target structure for which its actual loadings are unknown. The feasibility and practicality of the proposed method are evaluated from laboratory-model tests on free-free beams for which accelerations were measured before and after several damage cases.

• 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1A
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• pp.135-146
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• 2008

In this paper, a hybrid damage monitoring scheme for prestressed concrete (PSC) girder bridges by using sequential acceleration and impedance signatures is newly proposed. Damage types of interest include prestress-loss in tendon and flexural stiffness-loss in a concrete girder. The hybrid scheme mainly consists of three sequential phases: damage alarming, damage classification, and damage estimation. In the first phase, the global occurrence of damage is alarmed by monitoring changes in acceleration features. In the second phase, the type of damage is classified into either prestress-loss or flexural stiffness-loss by recognizing patterns of impedance features. In the third phase, the location and the extent of damage are estimated by using two different ways: a mode shape-based damage detection to detect flexural stiffness-loss and a natural frequency-based prestress prediction to identify prestress-loss. The feasibility of the proposed scheme is evaluated on a laboratory-scaled PSC girder model for which hybrid vibration-impedance signatures were measured for several damage scenarios of prestress-loss and flexural stiffness-loss.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.1
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• pp.81-89
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• 2012

This study propose the vibration-based damage monitoring scheme for steel girder bolt-connection member by using wireless acceleration sensor node. In order to achieve the objective, the following approaches are implemented. Firstly, wireless acceleration sensor node is described on the design of hardware components and embedded operation software. Secondly, the vibration-based damage monitoring scheme of the steel girder bolt-connection member is described. The damage monitoring scheme performed global damage occurrence alarming and damage localization estimation by the acceleration response feature analysis. The global damage alarming is applied to the correlation coefficient of power spectral density. The damage localization estimation is applied to the frequency-based damage detection technique and the mode-shape-based damage detection technique. Finally, the performance of the vibration-based damage monitoring scheme is evaluated for detecting the bolt-connection member damage on a lab-scale steel girder.