• Journal of the Korea Concrete Institute
• /
• v.25 no.5
• /
• pp.529-537
• /
• 2013

The aim of the current study is to develop a nonlinear isoparametric layered frame finite element (FE) analysis of FRP strengthened reinforced concrete (RC) beam or column members by a force-based FE formulation. In sections, concrete is modeled in the triaxial stress-strain relationship state and the FRP sheet is modeled as layered composite materials in two-dimension. The element stiffness matrix derived by the force-based FE has the force-interpolation functions without assuming the displacement shape functions. A lateral load test of RC column strengthened by GFRP sheets was analyzed by the developed force-based FE model. From comparative studies of the experimental and analysis results, it was shown to compare with the stiffness FE method that the force-based FE analysis could give more accurate predictions in the overall lateral load-deflection response as well as in nonlinear deformations and damages in the column plastic hinge region.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.1 no.1
• /
• pp.26-34
• /
• 2013

Durability performance in RC structures varies significantly with changes in cover depth and mix proportions. GGBFS (Ground Granulated Blast Furnace Slag) is very effective mineral admixture and widely used for an improved resistance to chloride attack. In this paper, characteristics such as porosity, compressive strength, and diffusion coefficient are evaluated in GGBFS concrete with 30~70% of replacement ratio and $4,000{\sim}8,000cm^2/g$ of fineness. Through the tests, more dense pore structure, higher compressive strength, and lower diffusion coefficient are obtained in GGBFS concrete, which are evaluated to be more dependent on replacement ratio than fineness. With increasing curing period from 3 to 91 days, porosity decreases to 77.47% and strength increases to 373% in GGBFS concrete. Chloride diffusion coefficient in GGBFS concrete decreases to 64.4% compared with that in OPC concrete, which shows significant improvement of durability performance.

• Journal of Korean Society of Steel Construction
• /
• v.21 no.1
• /
• pp.55-62
• /
• 2009

Blast cleaning has been applied in steel bridges for cleaning forged surface and increasing adhesive property of applied coating systems. Blasting is the operation of cleaning or preparing a surface by forcible propelling a stream of abrasive metals against it. Blast cleaning may improve surface geometry and induce compressive residual stress, and eventually may increase fatigue life of weld joints. In this paper, fatigue tests were carried out on three types of non-load-carrying fillet welded cruciform joints, as-welded joints, blast-treated joints, and stress-relieved joints after blasting, in order to investigate effect of blast cleaning on fatigue behavior of the weld joints. By Blast cleaning, the weld toe radius was increased by 29% and compressive residual stress was induced near weld toes. Blast cleaning increased fatigue life and fatigue endurance limit of the weld joints. When the applied stress ranges decreased, the increment in fatigue life became larger. About a 150% increase in fatigue limit could be realized by using blast cleaning.

• Journal of Bio-Environment Control
• /
• v.15 no.2
• /
• pp.190-195
• /
• 2006

The purpose of this study was to figure out the best condition in growth and sod quality of Mentha spp. according to cutting methods and soil depth. Applemint (M. suaveolens), Peppermint (M. piperita), and Spearmint (M. spicata) were used. Regardless of cultivar and soil depth condition, the growth rate in top cutting was higher than layering method. The difference between layering and layering without apical meristem was not significant. Optimal condition for growth was 5cm depth of soil. However, the shallower the depth of the soil, the better quality of sod. Among three Mentha species, M suavelens showed plant height and node number and M. piperita had shoot number were higher than other variety. The best condition of sod was top cutting and 1cm depth of soil regardless of cultivar.

• Proceedings of the Korean Professional Engineer Association Conference
• /
• 1995.10a
• /
• pp.46-68
• /
• 1995

근 반세기 동안에 세계에서 간척 사업이 가장 활발하였던 곳은 화란의 북해안과 우리 나라의 서남해안이다. 이는 한반도의 서해안을 말하는 것으로 북한까지 포함된 것을 말한다. 그간 우리 나라는 간척 사업에 의해 농지의 외연적인 확대로 쌀의 지급율을 높이는 데 일익을 담당한 것도 사실이다 우리 나라의 서해안은 간만의 차가 커서 \circled1간척지가 잘 발달되어 간척 적지가 많고, \circled2지구 내의 배수 방식이 외국에서처럼 기계 배수가 아니고 자연 배수가 가능하여 유지 관리비가 적게 든다. 그러나 \circled3 방조제. 축조시 불가피하게 강력한 조류속이 발생하지만 이에 견별 수 있는 자연 석재를 비롯하여 축제 재료의 구득이 용이하고, 돌망태 공법을 개발하여 공사가 용이하고 공사비도 저렴하다. 또한 태풍이나 해일에 의해 해면이 상승하는 기상조도 일본이나 화란의 3.5m인데 비해 우리 나라는 1.5m정도로 이들 나라에 비하여 같은 조건에서도 둑마루 높이가 2.0m정도가 낮아져 공사비도 저렴하고 외측 피복공 공사도 용이하다. 뿐만 아니라 서남 해안의 해안선은 굴곡이 심하고 연안에는 섬들이 산재하여 있어, 매립 면적당 방조제의 길이가 짧고, 공사의 단계별 추진이 용이하다. 간석지의 토질도 비교적 단단하여 방조제의 축조나 토지 이용에 적합하는 등, 자연적인 간척 여건은 세계에서 찾아볼 수 없는 천혜의 입지 조건을갖추고 있다. 그동안 우리 나라의 간척 기술은 8 . 15 광복 이후, 소규모 간척 사업을 시행하다가 60년대에 이르러 국가 경제 개발의 일환으로 추진된 동진강 간척사업을 필두로, 70년대에는 남양, 아산, 삽교천 방조제 공사를 시행하면서 우리 나라 여건에 부합되는 방조제 구조와 공법을 독자적으로 개발하였고, 80년대에는 영산강, 대호, 금강, 90년 초에는 영암방조제 공사들을 무리없이 성공시켰고, 독자적인 기술 개발이 촉진되어 1994년 1월에는 세계 간척사상 유출입 조석량이 가장 큰(9억m$^3$로 그간 우리나라 및 화란에서 시행하였던 큰 규모는 약 3~억 m$^3$ 내외임) 시화 방조제 끝막이 공사를 우리 나라가 개발한 구조와 공법으로 성공시켰으며, 이에 힘입어 유출입 조석량이 18억m$^3$인 새만금 간척 공사를 독자적인 우리 기술에 의해 계획대로 시행되고 있는 현시점에서 그간 우리 나라의 간척 기술개발 사항은 물론, 간척 사업 .전반적인 사항을 요약하였고, 세계 각국의 간척 사업과도 비교하여 우리나라 간척 사업에 대한 현주소를 여기에 소개한다.

• Journal of the Korea Concrete Institute
• /
• v.17 no.6 s.90
• /
• pp.893-902
• /
• 2005

Reasonable prediction of residual capacity of fire-damaged reinforced columns is important for both the safety measurement and the rehabilitation of the reinforced concrete structures suffered from exposure to extensive fire. In order to predict the residual behavior of fire-damaged reinforced concrete columns, its predictive model must be able to take into account the amount of heat transferred into the column, the level of deterioration of constituent materials and various column geometries. The numerical model presented in this research includes all these factors. The model has been shown to reasonably predict the residual behavior of fire-damaged columns. Parametric studies were performed using this model for the effects of cover thickness, exposure time to fire and column geometries on the residual behavior of reinforced concrete columns. It was found that serious damage on the residual capacity of column resulted from a longer exposure time to fire but only marginal differences from other factors.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.28 no.5
• /
• pp.563-570
• /
• 2015

The existing research on the damage detection method for building structures has considered the damages from the excessive loadings such as the earthquake. However, the structural performance of building structures could be reduced due to the deterioration based on the chloride, carbonation during the long-term time. Thus, to effectively manage the healthiness of structures, the deterioration influences on the structures should be checked. In this study, the corrosion of rebars by the chloride is considered as the deterioration factor. To consider the structural performance reduction of the corroded rebars, the yield strength, cross-sectional area, rupture strain of rebars and the compressive strength of cover concrete based on the corrosion level are estimated. These properties of rebars and cover concrete are used for the procedure to evaluate the structural performance reduction of structural member level and the building level. The moment-curvature analysis is performed to evaluate the structural performance reduction of structural member level. Also, the eigenvalue analysis and the pushover analysis are performed to investigate the natural period and mode shape and the strength and deformation performance of buildings, respectively.

• Korean Journal of Food Science and Technology
• /
• v.10 no.1
• /
• pp.8-10
• /
• 1978

After growing the hot pepper fruits in polyethylene film(PE) house covered with white or red colored film, the fruits were collected and chlorophyll, carotenoid, and capsaicin content was analyzed. Although total chlorophyll content was higher in fruit of white PE house$(208.9{\mu}g/g-F.W)$ as compared to that of red PE house $(153.0{\mu}g/g-F.W)$ grown plants, the ratio of chlorophyll a over b were similar, giving 2.15 and 2.13 respectively in white and red PE house. Total carotenoid, $\beta$-carotene and the capsaicin content were higher in fruits of red PE house grown plants. Therefore, it is suggested that red film could be used as a successful covering material for poly ethylene film house.

• Korean Journal of Plant Resources
• /
• v.13 no.2
• /
• pp.124-130
• /
• 2000

In an effort to produce high quality Angelica gigas NAKAI in the southern area of Korea, a variety of mulching materials were used to prevent withering during the summer. The experimental results are summarized as follows. Soil water content and temperature under various mulching materials were higher than those without mulching, in all the cases studied. Among various mulching materials P. E.(polyethylene) mulching material showed the highest effect. The appearance of weeds was the lowest when using the black P. E. mulching, while growth of weeds was the greatest when using transparent mulching. Growth and development of the plant were better with P. E. mulching than straw mulching or no mulching, allowed for more and bigger leaves. The bolting rate was about 2∼5%, with a slightly larger value under P. E. mulching. Under P. E. mulching, probably due to good physical properties of the soil the number of roots was large, and the length and diameter were good. Active growth of roots under P. E. mulching resulted in a yield increase of the plant. The black P. E. mulching material showed a prominent effect on suppression of weed growth, and the black P. E. material was considered to be the most recommendable among various P. E. mulching materials when there is a lack of labor.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2003.06a
• /
• pp.533-537
• /
• 2003

Compared to sintered polycrystalline diamond (PCD), the deposited thin film diamond has a great advantage on the fabrication of cutting tools with complex geometries such as drills. Because of high performance in high speed machining non-ferrous difficult-to-cut materials in the field of automobiles industry, aeronautics and astronautics industry, diamond-coated drills find large potentialities in commercial applications. However, the poor adhesion of the diamond film on the substrate and high surface roughness of the drill flute adversely affect the tool lift and machining quality and they become the main technical barriers for the successful development and commercialization of diamond-coated drills. In this paper, diamond thin films were deposited on the commercial WC-Co based drills by the electron aided hot filament chemical vapor deposition (EACVD). A new multiple coating technology based on changing gas pressure in different process stages was developed. The large triangular faceted diamond grains may have great contribution to the adhesive strength between the film and the substrate, and the overlapping ball like blocks consisted of nanometer sized diamond crystals may contribute much to the very low roughness of diamond film. Adhesive strength and quality of diamond film were evaluated by scanning electron microscope (SEM), atomic force microscope (AFM), Raman spectrum and drilling experiments. The ring-block tribological experiments were also conducted and the results revealed that the friction coefficient increased with the surface roughness of the diamond film. From a practical viewpoint, the cutting performances of diamond-coated drills were studied by drilling the SiC particles reinforced aluminum-matrix composite. The good adhesive strength and low surface roughness of flute were proved to be beneficial to the good chip evacuation and the decrease of thrust and consequently led to a prolonged tool lift and an improved machining quality. The wear mechanism of diamond-coated drills is the abrasive mechanical attrition.