• Journal of the Korean Geosynthetics Society
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• v.18 no.1
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• pp.67-77
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• 2019

The grouting method is utilized to reinforce and waterproof poor grounds, enhance the bearing capacity of structures damaged resulting from settlement due to elevation and vibration or differential settlement, and for cutoff. The purpose of this research is to enhance the compressive strength of grout materials by using aramid fiber and develop a high-strength ground improvement method by using blast furnace slag powder. In this regard, this study has conducted a uniaxial compression test after checking the high charge (higher than 50%) of the ratio of blast furnace slag powder and cement at 100:0, 70:30 and 40:60%, adding the aramid mixture based on 0, 0.5 and 1.0% of the cement and furnace slag powder weight and creating sand gels based on surface oiling rate of 0.7 and 1.2%. For the environmental review evaluation, a heavy metal exudation test and a pH test measurement have been conducted. The experiment results showed that 1% increase of aramid fiber led to 1.3 times greater uniaxial compression intensity. As for the hexavalent chrome, a 30% increase in blast furnace slag powder led to approximately 50% decrease in heavy metal exudation. However, the pH test revealed that a 30% increase in blast furnace slag powder resulted in approximately 0.5 increase in pH. Further research on the pH part is needed in the future.

• Journal of the Korean Geotechnical Society
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• v.22 no.8
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• pp.107-118
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• 2006

Among a variety of influencing components, time-variant seepage and long-term underground motion are important to understand the abnormal behavior of tunnels. Excessiveness of these two components could be the direct cause of severe damage on tunnels, however, it is not easy to quantify the effect of these on the behavior of tunnels. These parameters can be estimated by using inverse methods once the appropriate relationship between inputs and results is clarified. Various inverse methods or parameter estimation techniques such as artificial neural network and least square method can be used depending on the characteristics of given problems. Numerical analyses, experiments, or monitoring results are frequently used to prepare a set of inputs and results to establish the back analysis models. In this study, a back analysis method has been developed to estimate geotechnically hard-to-known parameters such as permeability of tunnel filter, underground water table, long-term rock mass load, size of damaged zone associated with seepage and long-term underground motion. The artificial neural network technique is adopted and the numerical models developed in the first part are used to prepare a set of data for learning process. Tunnel behavior, especially the displacements of the lining, has been exclusively investigated for the back analysis.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.399-407
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• 2010

The flexural behaviors of two types of beam members exposed to freeze-thaw cycles were evaluated. This study aims to examine the effect of freeze-thaw cycles on the behavior characteristics of reinforced concrete (RC) beams. For the purpose, a part of the beam specimens were damaged until yielding of tension reinforcement was reached, before they were exposed to 150 and 300 cycles of freeze-thaw. Cyclic tests, as well as monotonic tests, were conducted to evaluate the stiffness degradation characteristics when same cycle is repeated. The material tests showed that relative dynamic modulus of concrete exposed to 300 cycles of freeze-thaw moderately decreased to 86.8% of normal concrete, indicating that concrete used in this study has good durability against freeze and thaw damage. The results of monotonic tests showed reduction of flexural strength, ductility and stiffness of the beam specimens exposed to freeze-thaw cycles compared with those of the control speciments. In particular, BDF13 specimens, which had been subjected to artificial cracking damage, did not showed enough flexural strength to satisfy nominal moment required by current concrete structure design code. In the monotonic tests results, BF75 specimens exposed to freeze-thaw cycles showed 10% or more cyclic stiffness degradation. Therefore, it was thought that deformation of concrete in compression have to be considered in design process of members under cyclic load, such as seismic device.

• Journal of Energy Engineering
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• v.18 no.1
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• pp.49-55
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• 2009

Occurrence of hydrogen embrittlement could be one of the main obstacles for using structural equipment under hydrogen environment. It is required to develop assessment methods of hydrogen embrittlement for the metals used in production, storage, transmission and application utilities of hydrogen. The most probable method of hydrogen mass transmission is using existing natural gas pipeline. Base or weld part of the pipeline can be damaged by mixed gas of hydrogen in the pipeline. In this study small punch (SP) testing was employed to evaluate the hydrogen embrittlement behavior for a line pipe steel (API X65) with electrochemically hydrogen charged specimens. Results showed that the SP test can be a good candidate test method for hydrogen damage evaluation method. Strength of steel is known to be decreased with the level of hydrogen charging. However, for API X65 steel base metal need in this study, the effect of hydrogen to strength was not significant. It can be negligible regardless of the hydrogen contents in the steel. With this test different strength levels with various hydrogen charging conditions were observed. It can also be anticipated that more sensitive evaluation of material behavior be obtainable by the SP test method.

• Journal of Navigation and Port Research
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• v.35 no.10
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• pp.823-827
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• 2011

The present Common Structural Rules for double hull oil tanker is not included the residual strength, which is one of the functional requirements in design part of Goal-based new ship construction standards (GBS). The GBS will be enforced after July 1, 2016. The requirement related residual strength has the goal to build safe ship even if she has the specified damages due to marine accidents including collision and grounding. In order to assess the residual strength based on risk for structural damages according to GBS, tons of nonlinear FE analysis work taking into account various types of damage will be needed. The Smith's method, a kind of simplified method for the strength analysis is very useful for this purpose. In this paper, the residual strength assessments based on ultimate strength using Smith's method were carried out. The objected ship is VLCC with stranding damage in bottom structures. Also, the results were compared with that of nonlinear FE analysis using three cargo hold model.

• Korean Journal of Plant Resources
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• v.33 no.4
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• pp.337-364
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• 2020

Mt. Taegi (1,261.4 m) located in Gangwon-do, is a geographically important region for plant biodiversity. But the biodiversity of Mt. Taegi has been seriously damaged by the invasion of foreign plants, the development of forests and so on. We conducted 21 field surveys between April and August in 2008 and March and October in 2018 to investigate the vascular flora in Mt. Taegi. Total 662 taxa were identified including 96 families, 338 genera, 580 species, 4 subspecies, 66 varieties and 12 formas. Among them, 28 taxa were Korean endemic plants and 8 taxa were rare plants designated by the Korea Forest Services, and 11 taxa were listed on the Red list of endangered plants and 127 taxa were designated as the floristic regional indicator plants according to the Ministry of Environment. The alien plants were 45 taxa, including R. acetosella that is the ecosystem disturbing species.

• KEPCO Journal on Electric Power and Energy
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• v.6 no.2
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• pp.137-143
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• 2020

The CM247LC, a Ni-based superalloy material used for gas turbine hot gas path parts, is casted using directionally solidified technology to analyze the mechanical properties and microstructures through HIP (Hot Isostatic Pressing) and post-heat treatment, and to derive optimal HIP treatment conditions. The CM247LC material is being researched in various ways as an alternative material for prototyping gas turbine blades. In particular, the blade rotating part is exposed and operated in a high temperature and high-pressure environment, and when damaged, it may cause huge economic losses. Therefore, in order to use the CM247LC material as prototyping materials for gas turbine blades, the reliability of the microstructure and mechanical properties must be verified. In this study, after casting rod test specimens using CM247LC material by directionally solidified technology, after that the specimens were performed by HIP treatment and post-heat treatment to test two HIP conditions designed by KEPCO to derive the possibility of prototyping of CM247LC material and optimization of HIP treatment conditions. Additionally, the properties of CM247LC material were compared to the GTD111DS material using for 1,300℃ class gas turbine blades.

• Journal of the Korean Institute of Landscape Architecture
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• v.38 no.3
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• pp.53-61
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• 2010

The purpose of this paper is to devise a user management plan for tourism destinations in parts of park and open green spaces to prevent resource damage through depreciative behavior by tourists. Also, the possibility of the introduction of user management has been considered in order to complement this in these kinds of park and open green spaces. As explained in prior results, tourists have had the opportunity of taking part in many experiences which furnish cultural and historical information, but have never had experiences which furnish information in utilization and management such as prohibited behavior at tourism destinations, responsibility for damage, etc. The furnishing of information on utilization and management plays an important role in understanding responsibility in resource damage. For example, groups who have been given information on utilization and management appear to be much more responsible toward resources and environmental damage. For this reason, this must be a very important element for preventing damaging behavior at tourism destinations. Tourists can be made to understand that tourism destinations can be very seriously damaged by users. In order to control these damaging behaviors which occur from other users and to meet the needs of the tourism destinations being visited, it is necessary to establish a user management plan.

• Child Health Nursing Research
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• v.8 no.2
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• pp.183-194
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• 2002

This study was conducted to obtain a basic information related to a more systematic safety education and measures against children's accidents by a descriptive survey with regard to accidents actually experienced by elementary schoolers, their perceived safety education activities and school facilities to their safety lives. The data was collected among 1,654 pupils, belonging to the 5th and 6th grades in Pusan from Nov. 20 to Dec. 1, 2000. The data was analyzed using SPSSWIN(7.5). The results were as follows ; 1. According to the perception by elementary schoolers, they received safety life instruction at school in most cases from teachers in charge of their own class (41.0％). Such safety education was provided often during formal classes(24.4％). Traffic guidance was given by parents, highest in frequency(67.3％). 2. Matters as most often treated during safety life instruction were safety knowledge or dangerous things(37.5％). A majority of notices of school safety instruction were presented sometimes(48.4％). Source of knowledge about safety lives included teacher (35.3％), parents(32.9％), TV and newspaper (29.9％). As a source of knowledge of emergency treatment, school nurses were accounted for 41.3％ that was highest. 3.Among the 1,654 students, 91.8％ experienced at least more than one case of safety accident. The most frequent type and cause of safety accident were wound(33.7％). and self-carelessness(38.4％) respectively. In most cases, the subject experienced such accident during a break time(32.2％) and at a playgrounds. Part of body as most often damaged by accidents were arms and legs, 25.4％ higher than any other sides problem solving measures against the accident were taken by school nurse in most cases, 44.8％ in percentage point. 4. Those students' perceived safety management of school facilities showed that they considered classroom facilities as most safe (61.6％), while playground facilities as least safe(42.8％). They also responded that the treatment of glass fragments or stones at playground is the most important item of safety management.

• Journal of fish pathology
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• v.35 no.2
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• pp.167-176
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• 2022

We injected infectious myonecrosis virus (IMNV) to pacific whiteleg shrimp, Litopenaeus vannamei, and observed closely with using light microscope and transmission electron microscope (TEM) for 4-8 days post infection (dpi). As clinical signs, abdominal bodies had mild opaque muscles at 5 dpi. And the mortality was shown at 6 dpi. At 8 dpi, most injected shrimps had severe opaque muscles and humped back that cause of movement disorder. As results of histopathological examinations, local parts of abdominal body muscle had muscle fiber hyalinization, muscle fiber atrophy, rounded muscle fibers, myofibrillar hypertrophy in size, a decrease in number of myofibrils and phagocytosis from the sarcolemmas by multiple hemocytes at 4 dpi. Especially, myofibrillar hypertrophy appeared at the whole or random part of single muscle fiber not in specific locations like the center or edge of muscle fiber. At 6-7 dpi, multiple muscle necrosis, muscle fiber segmentation, myofibril lysis ap- peared and a few hemocytes were infiltrated at lesions. At 8 dpi, extensive muscle necrosis, multiple myofibril lysis and muscle fiber atrophy were shown, and very few hemocytes were infiltrated. In early stage of infection, local viral myositis with zenker's degeneration were shown. These lesions appeared multiply after the early stage. In late stage of infection, extensive coagulative muscle necrosis appeared with few of inflammatory response such as hemocytes infiltration. The lack of hemocytes infiltration response at the late stage might be disadvantage for Litopenaeus vannamei to defense against IMNV and to recover, because hematocytes (granulocyte, semi-granulocyte) eliminate pathogen and damaged tissues from infection sites and help recover. As results of the TEM observation, IMNVs that had nonenveloped icosahedral capsid which was 30-40 nm diameter were in myofibril and beside tubules of sarcoplasmic reticulum and moved to the certain direction. The micro-tears and micro-trau- mas in myofibrils caused muscle fiber necrosis. And semi-granulocytes engulfed IMNVs to eliminate virus.