• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.3
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• pp.21-30
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• 2021

Architectural cultural properties suffer a lot of damage due to various environmental factors. In order to preserve damaged cultural properties, preventive preservation and long-term preservation management are becoming more important. Therefore, research on a scientific non-destructive testing method applicable to regular inspection is required. For related research, DangGan with a high flag-pole shape was selected as the subject of study among various cultural properties. Among the preserved DangGans, a basic study was conducted on the analysis technique to evaluate the structural stability by selecting Treasure No. 49 Naju SeokDangGan. An idealized model was presented and a multi-degree of freedom equation of motion was derived. In addition, an equation for estimating the critical stiffness value for each joint position is presented.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.2
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• pp.185-190
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• 2006

This study carried out an evaluation of an oil tank that was defective in structure. This paper is divided into two sections which are analysis for the working process and suggestion for improving on the structure of the oil tank. As stated above, it has three major factors as to an improvement, such as the life cycle of structure (especially physical life cycle), and the many factors related to the duration years of the oil tank and analysis result. Based on this study, the improvement of oil tank was established. For example, the ground investigation needs before design and construction of oil tank, and constructing the oil tank by retaining wall type tank is good for maintenance. Also, it is important that the system for drainage is related to maintenance.

• Journal of the Korean Society of Safety
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• v.20 no.2 s.70
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• pp.119-126
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• 2005

Load bearing structural members in a wide variety of applications accumulate damage over their service life. From a standpoint of both safety and performance, it is desirable to monitor the occurrence, location, and extent of such damage. Structures require complicated element models with a number of degrees of freedom in structural analysis. During experiment much effort and cost is needed for measuring structural parameters. The sparseness and errors of measured data have to be considered during the parameter estimation Of Structures. In this paper we introduces damage identification algorithm by a system identification(S.I) using static and dynamic response. To study the behaviour of the estimators in noisy environment Using Monte Carlo simulation and a data measured perturbation scheme is adopted to investigate the influence of measurement errors on identification results. The assessment result by static and dynamic response were compared, and the efficiency and applicabilities of the proposed algorithm are demonstrated through simulated static and dynamic responses of a truss bridge. The assessment results by each method were compared and we could observe that the 5.1 method is superior to the other conventional methods.

• Magazine of the Korea Concrete Institute
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• v.10 no.6
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• pp.203-211
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• 1998

It is well recognized recently that acoustic emission, which is an elastic wave generated from rapid release of elastic energy in steressed solids, is very useful tool for on-line monitoring of microscopic behavior of deformation of material. In this study, three point bend test was performed to evaluate the microscopic damage progress during the loading and failure mechanism of mortar beam by monitoring the characteristic of AE signal. The relationship between AE characteristic and microscopic failure mechanism is discussed. In addition 2 dimensional AE source location based on triangular method was also done to monitor the intiation and propagation of micro crack around notch tip of mortar beam. It was shown that AE source location was very effective to predict the growth behavior of micro crack in mortar beam specimen.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.993-996
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• 2008

It has been reported that destruction test by core collection is the most reliable of the structural concrete strength in present building construction field. But it causes low efficiency by damage and cutting in structure due to the core collection. It also has some problems in repairing. Additionally in case of strength test with management specimen, different environment compared to the structure environment cause problems about estimation precise structure strength. Therefore, it is required to develop structure direct strength test that has test values and credibility above the ones obtained by core specimen collection strength test and seasonal specimen test to suggest a reasonable and practical management method of structural concrete.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.4
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• pp.9-16
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• 2010

In the health monitoring of civil engineering structures, the optimal sensor placement has a major influence on the quality of the results. This paper considers the problem of locating sensors with the aim of maximizing the data information so that structural parameters or damage of structures can be assessed. An proposed technique using a genetic algorithm is introduced to find the optimal placement of sensors. The sensitivity on modal vectors by structural parameters and the orthogonality of modal vectors have been taken as the fitness function of the genetic algorithm. A simple tower structure is used for example analyses to investigate the feasibility and applicability of the proposed approach. The example analyses show the way how the modal sensitivity and the modal orthogonality in the fitness function have influence on the optimal sensor placement. It is shown that the present method using the proposed fitness function can provide the reliable results.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.49 no.4
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• pp.23-30
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• 2012

This paper proposes an improved steganalysis method to detect the existence of secret message. Firstly, we magnify the small stego noise by multiplying the speckle noise to a given image and then we estimate the denoised image by using the soft thresholding method. Because the noises are not perfectly eliminated, some noises exist in the estimated cover image. If the given image is the cover image, then the remained noise will be very small, but if it is the stego image, the remained noise will be relatively large. The parent-child relationship in the wavelet domain will be slighty broken in the stego image. From this characteristic, we extract the joint statistical moments from the difference image between the given image and the denoised image. Additionally, four statistical moments are extracted from the denoised image for the proposed steganalysis method. All extracted features are used as the input of MLP(multilayer perceptron) classifier. Experimental results show that the proposed scheme outperforms previous methods in terms of detection rates and accuracy.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.1
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• pp.25-33
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• 1999

Since concrete is an inhomogeneous material consisting of larger aggregates and sand embedded in a cement paste matrix, it relatively shows a complex failure mechanism. In order to assure the reliability of concrete structure. microscopic fracture behavior and internal damage progress of concrete under the loading should be fully understood. In this study, an acoustic emission(AE) technique has been used to clarify microscopic failure mechanism and their corresponding AE signal characteristics of concrete under three-point bending test. In addition 2-dimensional AE source location has been performed to monitor the progress of an internal damage and the successive crack growth behavior during the loading. The relationship between AE signal characteristics and microscopic fracture mechanism is discussed.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.6 s.40
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• pp.73-80
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• 2004

A nonlinear time-domain system identification algorithm using measured acceleration data is developed for structural damage assessment. To take account of nonlinear behavior of structural systems, an output error between measured and computed acceleration increments has been defined and a constrained nonlinear optimization problem is solved for optimal structural parameters. The algorithm estimates time-varying properties of stiffness and damping parameters. Nonlinear response of restoring force of a structural system is recovered by using the estimated time-varying structural properties and computed displacement by Newmark-$\beta$ method. In the recovery, no pre-defined model for inelastic behavior has been assumed. In developing the algorithm, noise and incomplete measurement in space and state have been considered. To examine the developed algorithm, numerical simulation and laboratory experimental studies on a three-story shear building have been carried out.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.1
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• pp.97-108
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• 2013

Recently, mobile devices were increased and there was a sharp rise in demand. To exploit the location information of each device, many researcher was studying locating systems. The favorite locating or positioning systems were a GPS using satellites and a RTLS using wireless communication between devices. If some obstacle existed nearby the target device, The system have difference of performance. The obstacles near targets were caused signal disconnection and reflection because of NLOS condition. As the result, the NLOS condition degrade the locating performance. In this paper, we propose a locating system which is cooperated two systems using information reliability estimates from LOS/NLOS condition. We developed proposed system. In addition, we performed fields test and simulation tests at various environment for performance evaluation. As the result, the test showed 97% success rate to estimate NLOS condition. Furthermore, the simulation result of our locating system was increased to 89% compared with a single system.