• 건축역사연구
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• 제24권5호
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• pp.49-58
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• 2015

The purpose of this study is to analyze the overall condition of the foundation for the three storied stone pagoda of Bulguksa temple in GyeongJu. As a research method, exploration of the electrical resistivity, refraction seismic, surface wave exploration, GPR exploration, Reputation loading test. The results of the investigation, the range of the foundation was formed in foundation stone outskirts of 1.5 ~ 2.0m. It was confirmed to be about 2.0m depth. The depth of the foundation becomes shallower from the base portion to the outside. And the bearing capacity of foundation was sufficient conditions to weight. It can sufficiently support the weight of pagoda. And, the result of this investigation becomes basis data for repair work.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.1545-1561
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• 2008

Among all transportations, railway transports have been promisingly offering excellent energy conservation and travelling time. Inevitably, they become a main role in not only transport goods but also passengers. With leap in development of technology, trains have tremendously enhanced their services in terms of speed, accessibility and comfort. However, the safety and ride quality have become a main issue as the train speed increased. The higher speeds have led the structural dynamics and health must be monitored from time to time to ensure that they are in good condition to provide reliable ride. Among all monitoring systems, the structural health monitoring (SHM) systems are imperative important due to its capability of in-situ monitoring and inherently reduce the maintenance frequencies and the huge associated cost. In this paper, SHM systems and the related non-destructive test and evaluation methods were discussed. The types of damages related to train vehicles as well as the damage hot spots are also included in this paper.

• Structural Monitoring and Maintenance
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• 제6권3호
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• pp.173-190
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• 2019

Steel-confined reinforced concrete (SCRC) columns feature highly complex and invisible mechanisms that make damage evaluation and pattern recognition difficult. In the present article, the prevailing acoustic emission (AE) technique was applied to monitor and evaluate the damage process of steel-confined RC columns in a quasi-static test. AE energy-based indicators, such as index of damage and relax ratio, were proposed to trace the damage progress and quantitatively evaluate the damage state. The fuzzy C-means algorithm successfully discriminated the AE data of different patterns, validity analysis guaranteed cluster accuracy, and principal component analysis simplified the datasets. A detailed statistical investigation on typical AE features was conducted to relate the clustered AE signals to micro mechanisms and the observed damage patterns, and differences between steel-confined and unconfined RC columns were compared and illustrated.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 가을 학술논문 발표대회
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• pp.146-147
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• 2021

In this study, the deterioration of concrete subjected to high temperature was evaluated using harmonics. When concrete is exposed to high temperatures, its mechanical properties deteriorate. In order to evaluate this deterioration, a method of analyzing the waveform of elastic waves was applied. As the heating temperature increased, the fundamental wave of the 50 kHz elastic wave passing through the concrete decreased. In addition, harmonics were generated at each temperature, and the higher the heating temperature, the greater the ratio of harmonics. The higher the compressive strength, the greater the amplitude of the fundamental wave, and this phenomenon is thought to be due to the internal structure of concrete.

• Earthquakes and Structures
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• 제25권1호
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• pp.69-78
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• 2023

Life-cycle performance analysis of a reinforced concrete box section bridge was generated. Moreover, Monte Carlo simulation with important sampling (IS) was used to simulate the bridge material and load uncertainties. The bridge deterioration model was generated with the basic probabilistic principles and updated according to the measurement data. A genetic algorithm (GA) with the response surface model (RSM) was used to determine the deterioration rate. The importance of health monitoring systems to sustain the bridge to give services economically and reliably and the advantages of fiber-optic sensors for SHM applications were discussed in detail. This study showed that the most effective loss of strength in reinforced concrete box section bridges is corrosion of the reinforcements. Due to reinforcement corrosion, the use of the bridge, which was examined, could not meet the desired strength performance in 25 years, and the need for reinforcement. In addition, it has been determined that long-term health monitoring systems are an essential approach for bridges to provide safe and economical service. Moreover the use of fiber optic sensors has many advantages because of the ability of the sensors to be resistant to environmental conditions and to make sensitive measurements.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2022년도 가을 학술논문 발표대회
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• pp.183-184
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• 2022

In this study, harmonics of 100 kHz ultrasonic pulse transmitted through concrete exposed to high temperature were evaluated. Concrete exposed to high temperatures deteriorates its mechanical properties. In ultrasonic pulse, the fundamental wave was attenuated by the deterioration of the concrete. In addition, it was possible to confirm the occurrence of harmonics. It is thought that the fundamental and harmonics of ultrasonic pulse greatly affected by the internal structure of concrete.

• Journal of Forest and Environmental Science
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• 제30권4호
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• pp.351-361
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• 2014

Leaf area ($A_0$) and leaf biomass ($M_0$) estimation are significant prerequisites to studying tree physiological processes and modeling in the forest ecosystem. The objective of this study was to develop allometric models for estimating $A_0$ and $M_0$ of Swietenia mahagoni L. from different tree parameters such as DBH and tree height of mahogany plantations in the northeastern region of Bangladesh. A total of 850 healthy and well formed trees were selected randomly for sampling in the five study sites. Then, twenty two models were developed based on different statistical criteria that propose reliable and accurate models for estimating the $A_0$ and $M_0$ using non-destructive measurements. The results exposed that model iv and xv were selected on a single predictor of DBH and showed more statistically accuracy than other models. The selected models were also validated with an additional test data set on the basis of linear regression and t-test for mean difference between observed and predicted values. After that, a comparison between the best logarithmic and non-linear allometric model shows that the non-linear model produces systematic biases and underestimates $A_0$ and $M_0$ for larger trees. As a result, it showed that the bias-corrected logarithmic model iv and xv can be used to help quantify forest structure and functions, particularly valuable in future research for estimating $A_0$ and $M_0$ of S. mahagoni in this region.

• Corrosion Science and Technology
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• 제13권3호
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• pp.112-119
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• 2014

In this work, it is aimed to develop the fabrication method of axial stress corrosion cracking (SCC) defects having various sizes, on the outer diameter surface of the steam generator (SG) tubings. To control the length of the artificial SCC defect, the specific area of the SG tubing samples was exposed to an acidic solution after a sensitization heat treatment. During the exposure to an acidic solution, a direct current potential drop (DCPD) method was adopted to monitor the crack depth. The size of the SCC defect was first evaluated by an eddy current test (ECT), and then confirmed by a destructive examination. From the comparison, it was found that the actual crack length was well controlled to be similar to the length of the surface exposed to an acidic solution (5, 10, 20 or 30 mm in this work) with small standard deviation. From in-situ monitoring of the crack depth using the DCPD method, it was possible to distinguish a non-through wall crack from a through wall crack, even though the depth of the non-through wall crack was not able to be precisely controlled. The fabrication method established in this work was useful to simulate the SCC defect having similar size and ECT signals as compared to the field cracks in the SG tubings of the operating Korean PWRs.

• 대한기계학회논문집A
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• 제25권12호
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• pp.1911-1918
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• 2001

Recently the non-destructive test technique which uses the grain boundary etching characteristics owing to the variation of material structures has been proposed. However, during in-serviced GEM test there are a lot of variables such as the changes of temperature and concentration of etching solution, the roughness condition of surface polished etc.. The purpose of this paper is to investigate the influences of these test variables on GEM test results in order to establish a reliable and sensitive of GEM evaluation technique. The experiments are conducted in various solution temperatures, 10$\^{C}$, 15$\^{C}$, 20$\^{C}$, and 25$\^{C}$ and in 70% and 100% concentrations of that, and in various surface roughnesses polished by #800, #2000, and 0.3㎛ alumina powder. Through the test with variables, it is verified that the decrease of temperature and concentration of etching solution and the coarsened surface roughness by not using polishing cloth and powder induce some badly and/or greatly influences on GEM test results like grain boundary etching width(W$\_$GB) and intersecting point ratio(N$\_$i/N$\_$0/). Therefore, to get reliable and good GEM test results, it must be prepared the surface of specimen polished by polishing cloth and 0.3㎛ alumina powder and the saturated picric acid solution having 25$\^{C}$ and be maintained the constant temperature(25$\^{C}$) during GEM test.

• Structural Engineering and Mechanics
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• 제26권5호
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• pp.499-516
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• 2007

An experimental method denoted as Impulse Method is proposed as a cost-effective non-destructive technique for the on-site evaluation of concrete elastic modulus in existing structures: on the basis of Hertz's quasi-static theory of elastic impact and with the aid of a simple portable testing equipment, it makes it possible to collect series of local measurements of the elastic modulus in an easy way and in a very short time. A Hypothesis Testing procedure is developed in order to provide a statistical tool for processing the data collected by means of the Impulse Method and assessing the possible occurrence of significant variations in the elastic modulus without exceeding some prescribed error probabilities. It is based on a particular formulation of the renowned sequential probability ratio test and reveals to be optimal with respect to the error probabilities and the required number of observations, thus further improving the time-effectiveness of the Impulse Method. The results of an experimental investigation on different types of plain concrete prove the validity of the Impulse Method in estimating the unknown value of the elastic modulus and attest the effectiveness of the proposed Hypothesis Testing procedure in identifying significant variations in the elastic modulus.