• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.8
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• pp.693-701
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• 2016

In this study, notch defects are evaluated using fracture mechanics. To understand the effects of notch defects, FE analysis is conducted to predict the limit load and J-integral for middle-cracked and single-edge cracked plates with various sizes of notch under tension and bending. As the radius of the notch increases, the energy release rate also increases, although the limit load remains constant. The values of fracture toughness($J_{IC}$) of SM490A are determined for various notch radii through FE simulation instead of conducting an experiment. As the radius of the notch increases, the energy release rate also increases, together with a more significant increase in fracture toughness. To conclude, as the notch radius increases, the resistance to crack propagation also increases.

• Journal of Conservation Science
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• v.26 no.4
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• pp.385-395
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• 2010

This study aimed to identify weathering factors and to assess the conservation environment through microclimatic analysis of Hyeonpung Seokbinggo (ice-storing stone warehouse). The stone blocks inside Seokbinggo suffered crack, displacement, break-out, exfoliation, efflorescence, brown and black discoloration, and biological colonization. Biological colonization represented the maximum deterioration rate(24%) among those weathering forms. The indoor microclimate showed parallel patterns with outdoor one, but the indoor temperature and relative humidity ranged far narrower than outdoor and remained steady. The environmental characteristics resulted from blocking-out of outdoor heat by the closed entrance and surrounding microtopography. This prevented water condensation and freezing effects, so that it reduced physical deterioration of rock, and maximized ice-storing effect for long time. However, contrary to positive effect, extremely high relative humidity over 99% accelerated biological colonization inside the Seokbinggo.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.9
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• pp.1047-1052
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• 2012

Primary water stress corrosion cracking (PWSCC) instances have been reported in the Alloy 600 reactor pressure vessel head penetration nozzle and the Alloy 82/182 dissimilar metal butt weld nozzle in several PWRs. Therefore, in-service inspection programs have been adopted worldwide to prevent failure at the weld region. If a PWSCC is observed at the dissimilar metal weld region during inspection, its structural integrity should be evaluated; however, this requires considerable time and effort, and this might lead to a decrease in the plant utilization coefficient. To prevent this, KHNP-CRI have established integrity assessment criteria and developed a computer program for the fast evaluation and judgment of PWSCC. In this paper, the results and current status of the same are presented. Through this study, criteria for the structural integrity evaluation of PWSCC have been established, and a computer program has been developed to realize technical means for the evaluation of PWSCC structural integrity.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.755-767
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• 2020

A significant development has been made on a new fatigue damage model applicable to Gaussian wide band stress response spectra using numerical approximation methods such as data processing, time simulation, and regression analysis. So far, most of the alternative approximate models provide slightly underestimated or overestimated damage results compared with the rain-flow counting distribution. A more reliable approximate model that can minimize the damage differences between exact and approximate solutions is required for the practical design of ships and offshore structures. The present paper provides a detailed description of the development process of a new fatigue damage model. Based on the principle of the Gaussian wide band model, this study aims to develop the best approximate fatigue damage model. To obtain highly accurate damage distributions, this study deals with some prominent research findings, i.e., the moment of rain-flow range distribution MRR(n), the special bandwidth parameter μk, the empirical closed form model consisting of four probability density functions, and the correction factor QC. Sequential prerequisite data processes, such as creation of various stress spectra, extraction of stress time history, and the rain-flow counting stress process, are conducted so that these research findings provide much better results. Through comparison studies, the proposed model shows more reliable and accurate damage distributions, very close to those of the rain-flow counting solution. Several significant achievements and findings obtained from this study are suggested. Further work is needed to apply the new developed model to crack growth prediction under a random stress process in view of the engineering critical assessment of offshore structures. The present developed formulation and procedure also need to be extended to non-Gaussian wide band processes.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.1
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• pp.107-116
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• 2022

Recently, research has been actively conducted on the technology of inspection facilities through image-based analysis assessment of human-inaccessible facilities. This research was conducted to study the conditions of deep learning-based imaging data on bridges and to develop an evaluation prototype program for bridges. To develop a deep learning-based bridge damage detection prototype, the Semantic Segmentation model, which enables damage detection and quantification among deep learning models, applied Mask-RCNN and constructed learning data 5,140 (including open-data) and labeling suitable for damage types. As a result of performance modeling verification, precision and reproduction rate analysis of concrete cracks, stripping/slapping, rebar exposure and paint stripping showed that the precision was 95.2 %, and the recall was 93.8 %. A 2^nd performance verification was performed on onsite data of crack concrete using damage rate of bridge members.

• Smart Structures and Systems
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• v.31 no.4
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• pp.365-381
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• 2023

The existing vision-based techniques for inspection and condition assessment of civil infrastructure are mostly manual and consequently time-consuming, expensive, subjective, and risky. As a viable alternative, researchers in the past resorted to deep learning-based autonomous damage detection algorithms for expedited post-disaster reconnaissance of structures. Although a number of automatic damage detection algorithms have been proposed, the scarcity of labeled training data remains a major concern. To address this issue, this study proposed a semi-supervised learning (SSL) framework based on consistency regularization and cross-supervision. Image data from post-earthquake reconnaissance, that contains cracks, spalling, and exposed rebars are used to evaluate the proposed solution. Experiments are carried out under different data partition protocols, and it is shown that the proposed SSL method can make use of unlabeled images to enhance the segmentation performance when limited amount of ground truth labels are provided. This study also proposes DeepLab-AASPP and modified versions of U-Net++ based on channel-wise attention mechanism to better segment the components and damage areas from images of reinforced concrete buildings. The channel-wise attention mechanism can effectively improve the performance of the network by dynamically scaling the feature maps so that the networks can focus on more informative feature maps in the concatenation layer. The proposed DeepLab-AASPP achieves the best performance on component segmentation and damage state segmentation tasks with mIoU scores of 0.9850 and 0.7032, respectively. For crack, spalling, and rebar segmentation tasks, modified U-Net++ obtains the best performance with Igou scores (excluding the background pixels) of 0.5449, 0.9375, and 0.5018, respectively. The proposed architectures win the second place in IC-SHM2021 competition in all five tasks of Project 2.

• Journal of Life Science
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• v.25 no.2
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• pp.237-242
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• 2015

The use of calcite-forming bacteria (CFB) in crack remediation and durability improvements in construction materials creates a permanent and environmentally-friendly material. Therefore, research into this type of application is stimulating interdisciplinary studies between microbiology and architectural engineering. However, the mechanisms giving rise to these materials are dependent on calcite precipitation by the metabolism of the CFB, which raises concerns about possible hazards to cement-based construction due to microbial metabolic acid production. The aim of this study was to determine target microorganisms that possibly can have bio-corrosive effects on cement mortar and to assess multi-functional CFBs for their safe application to cement structures. The chalky test was first used to evaluate the $CaCO_3$ solubilization feature of construction sites by fungi, yeast, bacterial strains. Not all bacterial strains are able to solubilize $CaCO_3$, but C. sphaerospermum KNUC253 or P. prolifica KNUC263 showed $CaCO_3$ solubilization activity. Therefore, these two strains were identified as target microorganisms that require control in cement structures. The registered patented strains Bacillus aryabhatti KNUC205, Arthrobacter nicotianae KNUC2100, B. thuringiensis KNUC2103 and Stenotrophomonas maltophilia KNUC2106, reported as multifunctional CFB (fungal growth inhibition, crack remediation, and water permeability reduction of cement surfaces) and isolated from Dokdo or construction site were unable to solubilize $CaCO_3$. Notably, B. aryabhatti KNUC205 and A. nicotianae KNUC2100 could not hydrolyze cellulose or protein, which can be the major constituent macromolecules of internal materials for buildings. These results show that several reported multi-functional CFB can be applied to cement structures or diverse building environments without corrosive or bio-deteriorative risks.

• Journal of Conservation Science
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• v.18 s.18
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• pp.19-32
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• 2006

The stone pagoda of the Bunhwangsa temple made by piling small brick-shaped stones. The major rock forming stone bricks are andesites with variable genesis. Rock properties of the pagoda roof stone suffer partly including multiple peel-offs, exfoliation, decomposition like onion peels, cracks forming round lines and falling off stone pieces. The stylobates and tabernacles in all the four directions the pagoda are mostly composed of granitic rocks. Those rock properties are heavily contaminated by lichens and mosses with the often marks of inorganic contamination by secondary hydrates that are dark black or yellowish brown. Within the four tabernacles and northern pagoda body situated to relatively high humidity. There are even light gray precipitate looking like stalactites between the northern and western rocks of the body Their major minerals are calcite, gypsum and clays. The stone lion standing in the southeast and northeast side are alkali granite, while that in the southwest and northwest lithic tuff. Total rock properties of the pagoda are 9,708 pieces, among the all properties, fractured blocks are 11.0%, fall out blocks are 6.7% and covered blocks by precipitates are 7.0%, respectively. The pagoda has highly deteriorated the functions of the rock properties due to physical, chemical and biological weathering, therefore, we suggest that this pagoda has need to do long term monitoring and synthetic conservation researches.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.589-597
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• 2009

High Performance Fiber-reinforced Cement Composite (HPFRCC) shows the multiple crack and damage tolerance capacity due to the interfacial bonding of the fibers to the cement matrix. For practical application, it is needed to investigate the fractural behavior of HPFRCC and understand the micro-mechanism of cement matrix with reinforcing fiber. This study is devoted to the investigation of the AE signals in HPFRCC under monotonic and cyclic uniaxial compressive loading, and total four series were tested. The major experimental parameters include the type and volume fraction of fiber (PE, PVA, SC), the hybrid type and loading pattern. The test results showed that the damage progress by compressive behavior of the HPFRCC is a characteristic for the hybrid fiber type and volume fraction. It is found from acoustic emission (AE) parameter value, that the second and third compressive load cycles resulted in successive decrease of the amplitude as compared with the first compressive load cycle. Also, the AE Kaiser effect existed in HPFRCC specimens up to 80% of its ultimate strength. These observations suggested that the AE Kaiser effect has good potential to be used as a new tool to monitor the loading history of HPFRCC.

• The Journal of Engineering Geology
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• v.17 no.3
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• pp.393-404
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• 2007

The purpose of this study is to capture the essentials in survey and evaluation scheme which are able to assess the hazard of a rock slope systematically. Statistical analysis are performed on slope instability parameters related to failure of the rock slope. As the slope instability parameters, twelve survey items are considered such as tension crack, surface deformation, deformation of retaining structures, volume of existing failures, angles between strike of discontinuity and strike of cut slope face, angles between dip of discontinuity and dip of cut slope face, discontinuity condition, cut slope angle, rainfall or ground water level, excavation condition, drainage condition, reinforcement. A total of 233 road cut slopes located in Gyeongnam were considered. The stability of the road cut slopes were evaluated by estimating the slope instability index(SII) and corresponding stability rank. 126 rock slopes were selected to analyze statistical relation between SII and slope instability parameters. The multiple regression analysis was applied to derive statistical models which are able to predict the SII and corresponding slope stability rank. Also, its applicability was explored to predict the slope failures using the variables of slope instability parameters. The results obtained in this study clearly show that the methodology given in this paper have strong capabilities to evaluate the failures of the road cut slope effectively.