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Flexural Test for Prefabricated Composite Columns Using Steel Angle and Reinforcing Bar (앵글과 철근을 조립한 PSRC 합성기둥의 휨 실험)

  • Eom, Tae-Sung;Hwang, Hyeon-Jong;Park, Hong-Gun;Lee, Chang-Nam;Kim, Hyoung-Seop
    • Journal of Korean Society of Steel Construction
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    • v.24 no.5
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    • pp.535-547
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    • 2012
  • PSRC column is a concrete encased steel angle column. In the PSRC column, the steel angles placed at the corner of the cross-section resists bending moment and compression load. The lateral re-bars welded to steel angles resist the column shear and the bond between the steel angle and concrete. In the present study, current design procedures in KBC 2009 were applied to the flexure-compression, shear, and bond design of the PSRC composite column. To verify the validity of the design method and failure mode, simply supported 2/3 scaled PSRC and correlated SRC beams were tested under two point loading. The test parameters were the steel angle ratio and lateral bar spacing. The test results showed that the bending, shear, and bond strengths predicted by KBC 2009 correlated well with the test results. The flexural strength of the PSRC specimens was much greater than that of the SRC specimen with the same steel ratio because the steel angles were placed at the corner of the column section. However, when the bond resistance between the steel angle and concrete was not sufficient, brittle failures such as bond failure of the angle, spalling of cover concrete, and the tensile fracture of lateral re-bar occurred before the development of the yield strength of PSRC composite section. Further, if the weldability and toughness of the steel angle were insufficient, the specimen was failed by the fracture of the steel angle at the weld joint between the angle and lateral bars.

The Suggestion for Classification of Biotope Type for Nationwide Application (전국적 적용을 위한 비오톱유형분류 제안)

  • Choi, Il-Ki;Oh, Choong-Hyeon;Lee, Eun-Heui
    • Korean Journal of Environment and Ecology
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    • v.22 no.6
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    • pp.666-678
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    • 2008
  • The needs for drawing up of biotope map is rapidly spreaded over each local government recently in Korea, according as enhancing of interest about biotope, which is recognized to practical instrument for concretely being able to considering natural environment and ecosystem on all sorts of development plan. However, there are not yet the standard suggestion on biotope types and classification systems and biotope classification criteria. Therefore, each other methodologies are applied to each of local autonomies. First, under such critical mind the biotope types and classification systems were drafted by a review on biotope types, biotope classification systems, and biotope classification criteria of the preceded case studies until now at the inside and outside of the country. And then the purpose of this study is to derive biotope types and biotope classification systems applicable to the whole Korean region through continual feed back such as field surveys in selected representative areas and consultations. As a result of reviewing the case examples, first, the biotope classification systems were mixed two steps system with three steps system and those were composed mostly of the structure of two steps: large and small. Second, land-use, soil pavement ratio, green cover ratio, and vegetation usually were applied to the biotope classification criteria. This study suggests that the biotope classification system is consisted of four steps system: large(biotope class), medium(biotope group), small(biotope type) and detail(sub-biotope type), and the biotope types are classified into 13 types of large step, 45 types of medium step and 127 types of small step. However, this study suggests that the new biotope types on small step or detail step should be continually supplemented with the foundation of classification system proposed in this study because the biotope type classification should consider regional characteristics.

An Analysis of Rational Green Area Ratio by Land Use Types for Mitigating Heat-Island Effects (도시열섬완화를 위한 토지 이용 유형별 합리적 녹지율 분석)

  • SONG, Bong-Geun;PARK, Kyung-Hun
    • Journal of the Korean Association of Geographic Information Studies
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    • v.18 no.2
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    • pp.59-74
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    • 2015
  • The purpose of this study is to analyze reasonable green area ratios for mitigating urban heat island considering various land use types. Land uses of 5 types such as single residential, multi residential, commercial area, public facility, and industrial area were considered. Green areas were extracted from the tree attribution of land cover. Effect of urban heat island was analysed by the surface temperature of ASTER thermal infrared radiance scanned daytime and nighttime. Mitigation effect of green area at daytime was higher than nighttime. Surface temperature of green area was low in single residential at daytime. But the difference of surface temperature by each land use type was small. The effect of surface temperature mitigation of green area was lower in industrial area. The results of reasonable green area ratios for mitigating urban heat island indicate that surface temperature was the lowest with green area ratio of 40~50% in single residential, multi residential, and commercial area at daytime. Surface temperature of nighttime was not changed much by green area ratios. Therefore, the results of this study will be suggested in urban development planning to construct effectively green area for mitigating urban heat island.

Effect of Seeding Method and Mixing Ratio on the Quality and Productivity of Rye-Hairy Vetch Mixture (파종방법 및 혼파비율이 호밀-헤어리베치 혼파시 사료가치 및 생산성 향상에 미치는 영향)

  • Kim, J.G.;Yoon, S.H.;Chung, E.S.;Lim, Y.C.;Seo, S.;Seo, J.H.;Kim, S.J.
    • Journal of The Korean Society of Grassland and Forage Science
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    • v.22 no.4
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    • pp.233-240
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    • 2002
  • Hairy vetch(Vicia villosa Roth) which is legume fur winter cover crop can supply nitrogen for companion crop and soil. The purpose of this study was to improve the forage quality and productivity using forage crop and hairy vetch in winter season fer three years. The results of this experiments were summarized as follows. Plant height of rye was decreased but hairy vetch was increased. The heading stage of rye did not show difference among the treatments. The content of dry mater(DM) was decreased with increased ratio of hairy vetch/rye but it did not show significant difference between seeding methods. Crude protein(CP) content tended to increase in mixture plots. Acid detergent fiber(ADF) and NDF(neutral detergent fiber) content of mixture plots were lower than that of rye mono-cultivated. In vitro dry matter digestibility(IVDMD) and TDN(total digestible nutrient) content were showed inverted tendency. The highest DM yield was in rye mono-cultivated, but it was similar between mono-cultivated and mixture I (P<0.05). In the CP yield, it did not show the significant difference between rye mono-culture and mixture I . The content of total nitrogen in soil showed slight increase as 0.06∼0.08%. Conclusively, mixture I showed equal or superior productivity and quality comparing with rye mono-cultivated, mixture I would be recommended to produce higher yield and to conserve soil environment.

Estimation of the amount of refrigerant in artificial ground freezing for subsea tunnel (해저터널 인공 동결공법에서의 냉매 사용량 산정)

  • Son, Youngjin;Choi, Hangseok;Ko, Tae Young
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.20 no.2
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    • pp.255-268
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    • 2018
  • Subsea tunnel can be highly vulnerable to seawater intrusion due to unexpected high-water pressure during construction. An artificial ground freezing (AGF) will be a promising alternative to conventional reinforcement or water-tightening technology under high-water pressure conditions. In this study, the freezing energy and required time was calculated by the theoretical model of the heat flow to estimate the total amount of refrigerant required for the artificial ground freezing. A lab-scale freezing chamber was devised to investigate changes in the thermal and mechanical properties of sandy soil corresponding to the variation of the salinity and water pressure. The freezing time was measured with different conditions during the chamber freezing tests. Its validity was evaluated by comparing the results between the freezing chamber experiment and the numerical analysis. In particular, the freezing time showed no significant difference between the theoretical model and the numerical analysis. The amount of refrigerant for artificial ground freezing was estimated from the numerical analysis and the freezing efficiency obtained from the chamber test. In addition, the energy ratio for maintaining frozen status was calculated by the proposed formula. It is believed that the energy ratio for freezing will depend on the depth of rock cover in the subsea tunnels and the water temperature on the sea floor.

Evaluation of Field Applicability with Coal Mine Drainage Sludge (CMDS) as a Liner: Part I: Physico-Chemical Characteristics of CMDS and a Mixed Liner (차수재로의 광산슬러지 재활용 적용성 평가: Part I: 광산배수슬러지 및 혼합차수재의 물리·화학적 성질)

  • Lee, Jai-Young;Bae, Sun-Young;Woo, Seung-Hyun
    • Journal of the Korean Geosynthetics Society
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    • v.10 no.2
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    • pp.67-72
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    • 2011
  • CMDS (Coal Mine Drainage Sludge) is mainly generated from acid mine drainage during physicochemical treatment or electrical purification. CMDS is well worth considering on recycling possibilities in various areas. This research applies the liner and cover materials using waste disposal landfill generally to treat acid mine drainage sludge. In this Part I of the two parts paper, physico-chemical characteristics of CMDS, bentonite and cement to prepare the liner have been identified using XRD, XRF, FESEM. In addition, combining their physicochemical characteristics, the optimum mixing ratio has been determined to be 1: 0.5: 0.3 for CMDS: bentonite: cement by the batch tests. Initial permeability of CMDS was 7.10×107cm/s. Through the leaching test, it was confirmed that its mixture was environmentally safe. In the Part 2, a large-scale Lysimeter was used to simulate the effects of the layer on the freeze/thaw for evaluation on field applicability and stability.

Fire Resistance of Circular Internally Confined Hollow Reinforced Concrete Column (원형 내부 구속 중공 철근콘크리트 기둥의 내화 성능)

  • Won, Deok-Hee;Han, Taek-Hee;Lee, Gyu-Sei;Kang, Young-Jong
    • Journal of Korean Society of Steel Construction
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    • v.22 no.2
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    • pp.139-150
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    • 2010
  • Reinforced-concrete (RC) columns are frequently designed and constructed. other types of columns includes composite types such as concrete-filled tube columns (CFT). Hollow RC columns may be effective in reducing both the self weight of columns and total amount of materials used. This is due to the fact that a hollow RC column possesses larger moment of inertia than that of solid RC columns of same cross sectional area. Despite the effectiveness the hollow RC column has not been popular because of its poor ductility performance. While the transverse reinforcements are effective in controlling the brittle failure of the outside concrete, they are not capable of resisting the failure of concrete of inner face which is in unconfined state of stress. To overcome these drawbacks, the internally confined hollow reinforced concrete (ICH RC), a new column type, was proposed in the previous researches. In this study, the fire resistance performance of the ICH RC columns was analyzed through a series of extensive heat transfer analyses using the nonlinear-material model program. Also, effect of factors such as the hollowness ratio, thickness of the concrete, and thickness of the internal tube on the fire resistance performance were extensively studied. Then the factors that enhance the fire-resistant performance of ICH RC were presented and analyzed.

CO2 Evaluation of Reinforced Concrete Column Exposed to Chloride Attack Considering Repair Timing (보수시기를 고려한 염해에 노출된 콘크리트 교각의 탄소량 평가)

  • Kim, Seong-Jun;Kim, Young-Joon;Kwon, Seung-Jun
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.2 no.1
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    • pp.1-9
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    • 2014
  • In this paper, CO2 amount is evaluated considering repairing timing and unit CO2 amount per repair method including various stage of material manufacturing, moving, and construction. Four mix proportions with mineral admixture are considered and repairing timing/numbers are simulated based on the results from Life 365 which can handle chloride penetration. Furthermore two repair methods (simple cover concrete replacement and replacement with electro-chemical method for removing chloride content) are considered and the related CO2 emissions are evaluated. From the study, the case with high W/B (water to binder ratio) ratio shows smaller CO2 emission in construction stage but it increases more rapidly with increasing number of repair. CO2 emission considering electro-chemical method greatly increases with the increasing unit CO2 for the repairing method. The numbers of jumping step (repairing number) are evaluated to be 9 for WB37-OPC, 18 for WB50-OPC, 4 for WB40-SG, and 7 for WB47-SG respectively. RC structures with the longer maintenance free period are evaluated to be advantageous for saving CO2 emission.

Numerical Analysis on Liquefaction Countermeasure of Seabed under Submerged Breakwater Using Concrete Mat Cover (for Irregular Waves) (콘크리트매트 피복을 이용한 잠제하 해저지반에서의 액상화 대책공법에 관한 수치해석 (불규칙파 조건))

  • Lee, Kwang-Ho;Ryu, Heung-Won;Kim, Dong-Wook;Kim, Do-Sam;Kim, Tae-Hyung
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.29 no.1
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    • pp.20-35
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    • 2017
  • In the case of the seabed around and under gravity structures such as submerged breakwater is exposed to a large wave action long period, the excess pore pressure will be significantly generated due to pore volume change associated with rearrangement soil grains. This effect will lead a seabed liquefaction around and under structures as a result of the decrease in the effective stress, and eventually the possibility of structure failure will be increased. The study of liquefaction potential for regular waves had already done, and this study considered for irregular waves with the same numerical analysis method used for regular waves. Under the condition of the irregular wave field, the time and spatial series of the deformation of submerged breakwater, the pore water pressure (oscillatory and residual components) and pore water pressure ratio in the seabed were estimated and their results were compared with those of the regular wave field to evaluate the liquefaction potential on the seabed quantitatively. Although present results are based on a limited number of numerical simulations, one of the study's most important findings is that a safer design can be obtained when analyzing case with a regular wave condition corresponding to a significant wave of the irregular wave.

Development of Cloud Detection Method with Geostationary Ocean Color Imagery for Land Applications (GOCI 영상의 육상 활용을 위한 구름 탐지 기법 개발)

  • Lee, Hwa-Seon;Lee, Kyu-Sung
    • Korean Journal of Remote Sensing
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    • v.31 no.5
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    • pp.371-384
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    • 2015
  • Although GOCI has potential for land surface monitoring, there have been only a few cases for land applications. It might be due to the lack of reliable land products derived from GOCI data for end-users. To use for land applications, it is often essential to provide cloud-free composite over land surfaces. In this study, we proposed a cloud detection method that was very important to make cloud-free composite of GOCI reflectance and vegetation index. Since GOCI does not have SWIR and TIR spectral bands, which are very effective to separate clouds from other land cover types, we developed a multi-temporal approach to detect cloud. The proposed cloud detection method consists of three sequential steps of spectral tests. Firstly, band 1 reflectance threshold was applied to separate confident clear pixels. In second step, thick cloud was detected by the ratio (b1/b8) of band 1 and band 8 reflectance. In third step, average of b1/b8 ratio values during three consecutive days was used to detect thin cloud having mixed spectral characteristics of both cloud and land surfaces. The proposed method provides four classes of cloudiness (thick cloud, thin cloud, probably clear, confident clear). The cloud detection method was validated by the MODIS cloud mask products obtained during the same time as the GOCI data acquisition. The percentages of cloudy and cloud-free pixels between GOCI and MODIS are about the same with less than 10% RMSE. The spatial distributions of clouds detected from the GOCI images were also similar to the MODIS cloud mask products.