• 한국안전학회지
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• 제31권4호
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• pp.64-74
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• 2016

Recently, the seismic stability evaluation of concrete gravity dams is raised due to the failure of dams occurred by the Izmit, Turkey and JiJi, Taiwan earthquake in 1999. Dams failure may incur loss of life and properties around the dam as well as damage to dam structure itself. Recently, there has been growing much concerns about "earthquake - resistance" or "seismic safety" of existing concrete gravity dams designed before current seismic design provisions were implemented. This research develops three evaluation levels for seismic stability of concrete gravity dams on the basis of the evaluation method of seismic stability of concrete gravity dams in U.S.A., Japan, Canada, and etc. Level 1 is a preliminary evaluation which is for purpose of screening. Level 2 is a pseudo-static evaluation on the basis of the seismic intensity method. And level 3 is a detail evaluation by the dynamic analysis. Evaluation results on existing concrete gravity dams on operation showed good seismic performance under designed artificial earthquake(KHC earthquake).

• 한국해양공학회지
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• 제19권6호통권67호
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• pp.72-77
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• 2005

The materials used in a ship screw propeller are commonly made with brass. The seawater corrosion and seawater cavitation of the screw propeller reduces the propulsive performance of the ship. In screw manufacturing, the corrosion rust of the screw propeller is removed through a hand grinding method. The grinding process produces dust of the heavy metals from the brass. The dust creates a poor working environment that is harmful to the health of the workers. An automatic corrosionrust removing apparatus, using a blasting method, was developed for the improvement of screw polishing conditions and its working environment. The performance of this apparatus was investigated by surface roughness, weight loss rate, hardness, electrochemical corrosion resistance, and cavitation erosion, after removing of the corrosion rust under various blasting conditions. Two medias of alumina and emery were used in this experiment. The surface roughness and hardness of the screw were improved by this apparatus. The electrochemical corrosion potential (Ecorr) and current density (Icorr) were measured by the dynamic polarization method, using a potentiostat,under the conditions of surface polishing with grinding, blasting, wire brushing, and fine sand papering. The test results prove that the new corrosion rust-removing apparatus improves the surface performance of a screw propeller.

• The Plant Pathology Journal
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• 제27권1호
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• pp.26-32
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• 2011

Plant-pathogenic bacteria including Xanthomonas spp. carry genetic diversity in composition of avirulence genes for interaction with their host plants. Previously, we reported genetic diversity of avirulence genes in X. axonopodis pv. glycines. In this study, we determined genetic diversity of five avirulence genes, avrBs1, avrBs2, avrBs3, avrBs4, and avrRxv, in three other Xanthomonas species isolated in Korea by genomic southern hybridization. Although Korean races of X. campestris pv. vesicatoria that were isolated from year 1995 to 2002 had the same avirulence gene patterns as those that already reported, there was race shift from race 3 to race 1 by acquisition of avrBs3 genes. X. campestris pv. campestris isolated from Chinese cabbage, but not from cabbage or radish, carried two avrBs3 genes, and one of them affected HR-eliciting ability of this bacterium in broccoli. X. oryzae pv. oryzae carried eight to thirteen avrBs3 gene homologs, and this bacterium showed dynamic changes of resistance patterns in rice probably by losing or obtaining avrBs3 genes. These results indicate that avrBs3 gene is more diverse in Xanthomonas spp. than other four avirulence genes and also host ranges of these bacteria can be easily changed by loss or acquisition of avrBs3 genes.

• 한국건축시공학회지
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• 제6권2호
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• pp.73-79
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• 2006

The purpose of this study is to enhance the development of construction waste-recycling technologies and its economical efficiency by developing environment-friendly tetrapod, precast concrete, where recycled aggregate is used in order to promote recycling of waste concrete. The results of concrete mechanic characteristics experiments by the circulation coarse aggregate-replacement ratio are as the following. The circulation aggregate is lower and higher than natural aggregate in specific gravity and absorption ratio, respectively so that in case of mix proportioning, unit volume increases, while unit aggregate amount decreases. From the result, sufficient experiments of physical characteristics of circulation aggregate are required to get proper mix proportioning. When circulation aggregate-replacement ratio increases, compressive strength tends to decrease comprehensively, but 50% of replacement ratio is good enough to use. When circulation coarse aggregate's replacement ratio is 0%, drying shrinkage, which causes cracks in concrete and deteriorates durability, shows the minimum length change and the higher the ratio, the larger the length change. Thus. when using circulation coarse aggregate, drying shrinkage should be fairly examined. In freezing-and-thawing resistance, weight loss tends to comprehensively increase its loss at the circulation aggregate-mixed site. And the examination of surface aggregate-omission ratio is further needed and dynamic elastic modulus and durability factor(DF) require more study as well. In order to use circulation aggregate to tetrapod, a clear standard for strength should be first prepared and at the same time, more study about durability is needed.

• 수산해양기술연구
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• 제24권4호
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• pp.172-179
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• 1988

A cartridge type hydraulic logic valve consists of simple two port valve whose poppet is closed or opened by means of pressure signal of a pilot line. Accordingly, the logic valve can be used not only for direction, flow and pressure control purpose but also for versatile function valve which enables all above mentioned functions. In addition, the valve has little internal leakage and pressure loss, superior response characteristics and easiness in making small block type valve. The above mentioned good performances being recognized recently, the logic valve has been used widely in the large scale hydraulic system such as a hydraulic press system, for the performance requirements of high speed operation and precise control characteristics. However, there are scarce reports until now, except for a few ones from Aachen Institute of Technology in West Germany, so it is necessary to be studied on development and investigation for practical application. This paper showed that the static and dynamic characteristics of a logic valve when the logic valve is used for directional control, to investigate the relations between the valve operating characteristics and the valve design conditions. From the above mentioned procedure, it was ascertained that the valve operation characteristics obtained by numerical analysis showed good agreements with experimental results. The representative results obtained are as follows; 1. During the valve is closing, the poppet velocity is almost constant in the logic valve. 2. The pilot pressure P sub(3) and the resistance R in the pilot line have much influences on the valve operation time. 3. Spring strength have not such a severe influence on the valve operating time. 4. The operation characteristics of the logic valve can be estimated with good accuracy comparatively by numerical analysis with the equations describing poppet motion.

• 한국지진공학회논문집
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• 제6권1호
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• pp.33-41
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• 2002

최근 1995년 일본의 고베 및 1999년도에 터키와 대만 등지에서 일어난 강진으로 많은 사상자와 피해가 발생되었고 일본 및 대만의 경우 일부 댐의 피해가 발생되었다. 댐의 경우 지진 발생시 국부적인 구조물의 손상뿐만 아니라 주변 주거지역에 많은 인명피해를 유발하기 때문에 국내에서도 내진설계기준 강화 이전의 콘크리트 중력식 댐에 대한 내진 안전성 평가의 필요성을 인식하게 되었다. 본 연구에서는 미국, 일본 및 캐나다의 내진설계기준 및 안전성 평가기법을 분석하여 국내 실정에 적합한 내진 안전성 평가 지침을 마련하였다. 평가단계는 제3단계로 구성하였다. 제1단계는 기초 문헌자료를 이용한 내진 안전성 평가 필요여부를 구분하는 예비평가단계이며 제2단계 평가는 진도법을 적용한 유사정적해석을 수행하여 성능기준 만족여부를 판단한다. 제3단계 평가는 제2단계를 만족하지 못하였을 경우 대상구조물에 동적해석을 적용하여 정밀한 평가를 수행한 후 성능기준을 평가한다. 본 연구에서는 현재 국내에서 운영중인 콘크리트 중력식 댐을 선정하여 본 평가 방법을 적용하였다.

• 한국지반환경공학회 논문집
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• 제15권2호
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• pp.37-43
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• 2014

지진 및 해일과 같은 자연재해는 갑작스럽게 발생하므로 막대한 인명 피해 및 재산피해를 야기한다. 특히 지진은 이에 동반된 광범위한 피해로 인하여 특히 심각한 위협이 된다. 국내의 경우 비탈면 설계 및 시공 시 내진설계가 거의 적용되지 않고 있다. 하지만 점차적으로 내진에 대하여 중요성을 인지하고 이에 대한 연구가 이루어지고 있다. 비탈면의 안정화를 위한 공법 중 쏘일 네일 공법은 타 공법에 비해 시공성, 경제성이 우수한 공법으로 비탈면 안정을 위한 보강공사에도 광범위하게 이용되고 있다. 이러한 공법에 대한 연구는 네일과 주변지반의 상호거동에 대한 연구가 진행되고 있으며, 정하중 및 동하중 등의 다양한 하중조건에서의 안정성에 대한 연구가 활발히 진행되고 있다. 그럼에도 불구하고, 네일 두부의 구속조건에 따른 네일과 비탈면과의 상호거동에 대한 연구는 미비한 실정이다. 이에 본 연구에서는 네일 두부 구속조건에 따른 보강 비탈면의 안정성에 미치는 영향을 확인하기 위해 수치해석을 수행하였다. 그 결과 지진하중에 대하여 네일 두부가 구속된 경우가 비구속된 경우에 비해 지진하중에 대하여 저항이 큰 것으로 나타났다.

• 한국건설순환자원학회논문집
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• 제7권4호
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• pp.438-444
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• 2019

본 연구에서는 모르타르의 동결융해피해에 미치는 폴리프로필렌섬유의 영향을 실험적으로 검토하였다. 섬유를 혼입하지 않은 섬유무보강 모르타르와 폴리비닐알코올섬유를 혼입한 모르타르를 비교 대상으로 하여 폴리프로필렌섬유의 혼입이 300사이클의 동결융해시험 후 모르타르의 압축 및 휨특성에 미치는 영향을 평가하였다. 또한, 300사이클의 동결융해 시험 후 모르타르의 질량감소율, 상대동탄성계수 및 공극크기분포에 대한 시험을 실시하였다. 그 결과, 섬유종류에 관계없이 섬유무혼입 모르타르에 비해 섬유혼입 모르타르는 300사이클의 동결융해시험 후 압축강도 및 휨강도의 역학적 성능저하와 질량감소율의 증가를 억제하는 것이 가능했다. 한편, 300사이클의 동결융해시험 후 모르타르의 공극감소에 대한 저항에 폴리비닐알코올섬유뿐만 아니라 폴리프로필렌섬유가 효과적으로 작용할 수 있는 것을 확인했으나 폴리프로필렌섬유를 혼입한 모르타르의 동결융해저항성을 향상시키기 위해서는 폴리비닐알코올섬유에서 기대할 수 있는 시멘트매트릭스와의 결합효율을 증가시킬 필요가 있다.

• 한국도로학회논문집
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• 제17권2호
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• pp.1-11
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• 2015

PURPOSES : This study set out to investigate the fundamental properties of alkali-activated concrete (AAC) using modified slag as the pavement maintenance material. METHODS: The material properties of modified slag based alkali-activated concrete (MSAAC) were analyzed and evaluated against those of alkali-activated slag concrete (AASC). Several mix formulations were considered, including one MSACC and four AASCs. The main variables considered in the study were slump, air content, compressive strength, rapid chloride permeability test, scaling resistance, freeze-thaw test, XRD, SEM, and EDS. RESULTS: MSAAC exhibits a compressive strength in excess of 21 MPa six hours after curing. Also, the charge passed of the MSACC was found to be less than 2000 coulombs after seven days and about 1000 coulombs after 28 days. The weight loss determined from a scaling test did not exceed $1kg/cm^2$ in the case of the MSACC, but that of the AASCs had already exceeded $1kg/cm^2$ at the 10th cycle. Based on the results of the freeze-thaw test, the relative dynamic modulus of every mix was found to be in excess of 90%. An energy dispersive spectroscopy(EDS) analysis found that the weight rate percentage of the calcium and aluminum in the MSAAC mix is twice that of the AASC mixes. CONCLUSIONS : It was found that the MSAAC mix exhibits significantly better performance than AASC mixes, based on various fundamental properties.

• 소성∙가공
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• 제25권1호
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• pp.36-42
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• 2016

Fiber metal laminates (FMLs) are well known for improved fatigue strength, better impact resistance, superior damage tolerance and slow crack growth rate compared to traditional metallic materials. However, defects and loss of strength of a composite material can occur due to the vertical load from the punch during the joining with a dissimilar material using a conventional clinching method. In the current study, tapered-hole clinching was an alternative process used to join Al 5052 and FMLs. The tapered hole was formed in the FML before the joining. For the better understanding of static and dynamic characteristics, a clinched joining followed by a tensile-shear test was numerically simulated using the finite element analysis. The design parameters were also evaluated for the geometry of the tapered hole by the Taguchi method in order to improve and compare the lateral joining strength of the clinched joint. The influence of the neck thickness and the undercut were evaluated and the contribution of each design parameter was determined. Then, actual experiments for the joining and tensile-shear test were conducted to verify the results of the numerical simulations. In conclusion, the appropriate combination of the design parameters can improve the joining strength and the cross-sections of the tapered-hole clinched joint formed in the actual experiments were in good agreement with the results of the numerical simulations.