• Title, Summary, Keyword: neutral axis

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An Examination of the Maximum Steel Ratio for Reinforced Concrete Flexural Members: Focused on Singly Reinforced Beam with Rectangular Cross-section (철근콘크리트 휨부재의 최대철근비에 대한 고찰: 단철근 직사각형보를 중심으로)

  • Lee, Jun-Seok;Kim, Woo;Choi, Seung-Won
    • Journal of the Korea Concrete Institute
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    • v.29 no.2
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    • pp.179-187
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    • 2017
  • The design provisions for the maximum steel ratio in reinforced concrete flexural members is normally provided to ensure sufficient ductility and economy by steel yielding at member failure. In the Concrete Structural Design Code (2012), the maximum steel ratio is expressed in terms of a net strain in tensile steel, and leading to very high steel ratio in the case of using high strength materials. Thereby, this may result in difficulty to satisfy a required workability at concrete placing. On the contrary, in the Korean Highway Bridge Design Code (Limit State Design) the maximum steel ratio is given in terms of the maximum neutral axis depth ratio that is 0.4. From these results, a rational model for the maximum steel ratio is suggested so as to satisfy a ductility as well as a workability.

A Study on the Calculation Method for Flexural Strength of One-way Hollow Slabs (일방향 중공슬래브의 휨강도 산정방법에 관한 연구)

  • Kim, Hyun-Su;Lim, Jun-Ho;Kang, Joo-Won
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.25 no.6
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    • pp.541-548
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    • 2012
  • The hollow slab has advantages that its self-weight does not greatly increase notwithstanding the increase of its thickness and its flexural performance does not significantly degrade in comparison with general reinforced concrete slab. However, the utilization of the hollow slab is currently being underestimated in spite of structural system that enables economic design of building and construction of eco-friendly structure. the significant reasons for this situation is that the method of structural analysis and design for hollow slab is not generalized. In this study, to consider practical compressive zone of hollow slab, the equation for its flexural strength is proposed by the volume of compressive stress block according to neutral axis location in hollow section assumed. Existing estimation method of flexural strength of hollow slab considering only compressive zone above hollow part is evaluated as the most conservative method and the method estimating flexural strength by two alternative cross-section of hollow slab is evaluated as more practical method.

Optimum Slab-Lifting Positions for Precast Concrete Pavement Construction (프리캐스트 콘크리트 포장 시공 시 최적 슬래브 리프팅 위치)

  • Kim, Seong-Min;Cho, Byoung-Hooi;Han, Seung-Hwan
    • International Journal of Highway Engineering
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    • v.9 no.2
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    • pp.27-37
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    • 2007
  • This research was conducted to determine the optimum lifting positions on precast concrete slabs for precast concrete pavement construction, based on the analysis of concrete stress distribution under various lifting conditions. To analyze stresses in concrete slabs, the finite element method was implemented and a numerical model of the precast slab that was going to be used in the experimental construction was developed. Changes in the stress distribution due to the lifting angle were investigated because slab lifting is not always performed in the perpendicular direction to the slab surface. In addition, the effect of the lifting level, the distance between the neutral axis of the slab and the lifting point, on the stress distribution was investigated since the lifting point is not always at the neutral axis of the slab. To consider the actual steel design of the precast slab, the effect of the reinforcement near the lifting point was also investigated. From this study, the optimum lifting positions of the precast slabs were determined according to the lifting angle and level, and the results were compared with the lifting positions used in the PCI standards.

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Simplified Moment-Curvature Relationship Model of Reinforced Concrete Columns Considering Confinement Effect (구속효과를 고려한 철근 콘크리트 기둥의 모멘트-곡률 관계 단순모델)

  • Kwak, Min-Kyoung;Yang, Keun-Hyeok
    • Journal of the Korea Concrete Institute
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    • v.28 no.3
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    • pp.279-288
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    • 2016
  • The present study simplified the moment-curvature relationship to straightforwardly determine the flexural behavior of reinforced concrete (RC) columns. For the idealized column section, moments and neutral axis depths at different stages(first flexural crack, yielding of tensile reinforcing bar, maximum strength, and 80% of the maximum strength at the descending branch) were derived on the basis of the equilibrium condition of forces and compatibility condition. Concrete strains at the extreme compression fiber beyond the maximum strength were determined using the stress-strain relationship of confined concrete, proposed by Kim et al. The lateral load-displacement curves converted from the simplified moment-curvature relationship of columns are well consistent with test results obtained from column specimens under various parameters. The moments and the corresponding neutral axis depth at different stages were formulated as a function of longitudinal reinforcement and transverse reinforcement indices and/or applied axial load index. Overall, curvature ductility of columns was significantly affected by the axial load level as well as concrete compressive strength and the amount of longitudinal and transverse reinforcing bars.

Studies on the Lipid Metabolism of Soybean during its Germination-(Part 2) Changes on lipoxygenase activity and fatty acid composition in soybean during germination- (대두발아(大豆發芽)중 지질대사(脂質代謝)에 관한 연구-제2보(第2報) Lipoxygenase activity 및 지방산(脂肪酸)의 변화에 관하여-)

  • Shin, Hyo-Sun
    • Applied Biological Chemistry
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    • v.17 no.4
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    • pp.247-256
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    • 1974
  • The Merit variety of soybean (Glycine max L.), harvested in 1971 was germinated in the dark at $21{\sim}25^{\circ}C$ for 10 days. The soybean sprout were divided into cotyledons and seedling axis and subjected to the determination of lipoxygenase activity and fatty acid composition of triglycerides, free fatty acids, phosholipids and crude fat fractions at two-day intervals during the germination periods. The results are summarized as follows 1) The lipoxygenase activity in cotyledons declined sharply after second day, but the activity in seedling axis inclined slightly after second day. However, the decrease of lipoxygenase activity in cotyledons coincided with decrease of linoleic and linolenic acids in cotyledons and increase of lipoxygenase activity in seedling axis coincided with increase of those acids in seedling axis. 2) The iodine value of neutral fat in cotyledons decreased continuously, but the iodine value of the neutral fat in seedling axis remained almost constant. iodine value in cotyeldons was greater than in seedling axis. 3) In the fatty acid composition of triglycerides in cotyledons, palmitic acid did not changes significantly, stearic acid increased continuously, oleic acid changed irregularly, linoleic and linolenic acids continuously decreased significantly. But in the fatty acid composition of triglycerides in seedling axis, palmitic acid remained unchanged, linoleic and linolenic acids slightly increased continuously, stearic and oleic acids changed irregularly. 4) Composition of free fatty acids in cotyledons and seedling axis changed irregularly, suggesting that all fatty acids produced by hydrolysis of triglycerides by lipase are used(or either biosynthetic Purpose or energy Production at random. 5) Fatty acids with odd-numbered carbon chain were not detected in the triglycerides and free fatty acid fractions during the germination periods, suggesting that all fatty acids are utilized as $C_2$-unit in degradation and biosynthesis. 6) The changes of fatty acids composition of Phospholipid in cotyledons and seedling axis during the germination were similar to these of triglyceride fraction.

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Evaluation of scale accuracy and effect of off-the-visual-axis on schematic retinoscope training eye (검영기 훈련 모형안의 굴절상태 눈금과 벗어난 시축의 평가)

  • Ryu, Dong-Kyu
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.11 no.10
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    • pp.3789-3793
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    • 2010
  • To investigate accuracy of graduated scale of schematic retinoscope training eye(schematic eye) and induced effect when measured at off-axis from visual axis. Two skilled retinoscopist measured refractive power using retinoscope in random order. Seven schematic eyes from a single manufacturer were recruited and set to mark +4.00 to -6 diopter(+4, +3, +2, +1, 0, -1, -2, -3, -4, -5, -6). After introducing +2.00 diopter trial lens(50cm working lens), neutral distance was measured at 180 degree to estimate accuracy of scale, and refractive power measured at 0, 5, 10, 15 and 20 degree off-axis to see if any error was induced. According to the results measured by two specialists, in six of seven schematic eye, scale setting varied (p<0.05) and measured refractive power at 5, 10, 15 and 20 degree off-axis from visual axis were $-0.13{\pm}0.06$, $-0.29{\pm}0.06$, $-0.58{\pm}0.11$, and $-0.83{\pm}0.16$ diopter respectively. In some schematic eye, scale graduated on the schematic eye and scale measured by retinoscopy could be different and if retinoscopy is performed off-axis from visual axis, any measuring error can be caused.

The Study of Growth and Characterization of CuGaSe$_2$ Sing1e Crystal Thin Films for solar cell by Hot Wall Epitaxy (HWE(Hot Wall Epitaxy)에 의한 태양 전지용 박막성장과 특성에 관한 연구)

  • 홍광준
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.237-242
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    • 2001
  • The stochiometric mix of evaporating materials for the CuGaSe$_2$ single crystal thin films was prepared from horizontal furnace. To obtain the single crystal thin films, CuGaSe$_2$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperature were 610$^{\circ}C$ and 450$^{\circ}C$, respectively The crystalline structure of single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). From the photocurrent spectrum by illumination of perpendicular light on the c-axis of the CuGaSe$_2$ single crystal thin film, we have found that the values of spin orbit splitting Δ So and the crystal field splitting ΔCr were 91 meV and 249.8 meV at 20 K, respectively. From the Photoluminescence measurement on CuGaSe$_2$ single crystal thin film, we observed free excition (Ex) existing only high quality crystal and neutral bound exiciton (D$^{\circ}$,X) having very strong peak intensity. Then, the full-width-at-half-maximum(FWHM) and binding energy 7f neutral acceptor bound excision were 8 meV and 35.2 meV, respectivity. By Haynes rule, an activation energy of impurity was 355.2 meV

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The Cellulose Washing Finish of Blue Jeans (Part ll) the comparison of various fabrics- (청바지의 세탁가공에 관한 연구(제2보) -직물의 종류를 중심으로-)

  • 신혜원;유효선
    • Journal of the Korean Society of Clothing and Textiles
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    • v.21 no.7
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    • pp.1196-1204
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    • 1997
  • Cotton, rayon/cotton, and Tencel twill weave fabrics were used to investigate the effect of fiber types on the cellulase washing finish. And twill. basket, and derivative weave cotton fabrics were used to study the weave effect. Various fabrics were treated with neutral cellulase varying treatment times and with acid cellulase, stone, and stone-neutral cellulase respectively for two hours in a rotary washer. Weight loss decreased in the order of rayon/cotton> cotton> Tencel, and basket and derivative weave fabrics lost more weight than twill weave fabric. Color difference decreased in the order of cotton> Tencel> rayon/cotton, and twill weave fabric had larger color difference than derivative and basket weave fabrics. Back staining decreased in the order of cotton> rayon/cotton> Tencel, and twill weave fabric had larger back staining than derivative and basket weave fabrics. Tear strength retention decreased in the order of rayon/cotton> cotton> Tencet and twill weave fabric had larger tear strength retention than derivative and basket weave fabrics. Flex stiffness retention decreased in the order of cotton> Tencel> rayon/cotton, and in the order of derivative> twill> basket weave. In cotton fibers, damage of primary wall was observed. And the cellulase treatment on Tencel seemed to roughen the fabric surface slightly, and to fibril fibers along the fiber axis.

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TRIO (Triplet Ionospheric Observatory) CINEMA

  • Lee, Dong-Hun;Seon, Jong-Ho;Jin, Ho;Kim, Khan-Hyuk;Lee, Jae-Jin;Jeon, Sang-Min;Pak, Soo-Jong;Jang, Min-Hwan;Kim, Kap-Sung;Lin, R.P.;Parks, G.K.;Halekas, J.S.;Larson, D.E.;Eastwood, J.P.;Roelof, E.C.;Horbury, T.S.
    • Bulletin of the Korean Space Science Society
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    • pp.42.3-43
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    • 2009
  • Triplets of identical cubesats will be built to carry out the following scientific objectives: i) multi-observations of ionospheric ENA (Energetic Neutral Atom) imaging, ii) ionospheric signature of suprathermal electrons and ions associated with auroral acceleration as well as electron microbursts, and iii) complementary measurements of magnetic fields for particle data. Each satellite, a cubesat for ion, neutral, electron, and magnetic fields (CINEMA), is equipped with a suprathermal electron, ion, neutral (STEIN) instrument and a 3-axis magnetometer of magnetoresistive sensors. TRIO is developed by three institutes: i) two CINEMA by Kyung Hee University (KHU) under the WCU program, ii) one CINEMA by UC Berkeley under the NSF support, and iii) three magnetometers by Imperial College, respectively. Multi-spacecraft observations in the STEIN instruments will provide i) stereo ENA imaging with a wide angle in local times, which are sensitive to the evolution of ring current phase space distributions, ii) suprathermal electron measurements with narrow spacings, which reveal the differential signature of accelerated electrons driven by Alfven waves and/or double layer formation in the ionosphere between the acceleration region and the aurora, and iii) suprathermal ion precipitation when the storm-time ring current appears. In addition, multi-spacecraft magnetic field measurements in low earth orbits will allow the tracking of the phase fronts of ULF waves, FTEs, and quasi-periodic reconnection events between ground-based magnetometer data and upstream satellite data.

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