• Journal of the Korea Concrete Institute
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• v.29 no.4
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• pp.335-343
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• 2017

This paper aims at investigating the bending strength of high-strength concrete beams with compressive strength of 80 MPa. The experimental parameters included nominal yielding strength of rebar with 400 and 600 MPa, rebar ratio ranging from 0.98 to 1.97%, and shear span-effective depth ratios (a/d) of 6.0 and 4.8. Experimental results were discussed regarding load-deflection relationship, ductility, bending strength, and prediction of bending strength of beams. Test results indicate that the use of high-strength rebar increased bending strength but decreased ductility. As span-effective depth ratio increased, the ductility of test beams decreased. In addition, test results of bending strength were compared with predictions from the current KCI code, Eurocode 2 and Korean Highway Design Specification (KHDC). The design code predictions for bending strength underestimated the experimental results. Therefore, the current design code predictions for bending strength of high-strength concrete beams would provide conservative design. Predictions of bending strength from KCI code using strength reduction factors and those from Eurocode 2 as well as KHDC using material factors were similar each other.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.3
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• pp.237-243
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• 2015

In this study, the effects of the mixing ratio of emulsified fuel on the droplet evaporation and spray behavior characteristics were analyzed. A surfactant comprising span 80 and tween 80 mixed at a 9:1 ratio was used for the emulsified fuel. The fuel and surfactant were mixed at a ratio of 3:1 for the emulsified fuel. In addition, considering the mixing ratio of the surfactant, the mixing ratio of $H_2O_2$ in the emulsified fuel was set as EF (emulsified fuel)0, EF2, EF12, EF22, EF32, and EF42. To observe the evaporation characteristics, droplets of the emulsified fuel were dropped on a heating plate and observed using scattered light and a Schlieren system. In addition, to analyze the effect of the $H_2O_2$ mixing ratio, the behavior characteristics of the evaporative free spray were investigated in the mixing ratio range of EF0 to EF22 using a constant volume chamber with heaters. Consequentially, it was found that in the case of EF22, the free spray development of the emulsified fuel was faster than that of EF0 (diesel only) because of the promotion of the evaporation due to the phase change in the peroxide contained in the emulsion fuel.

• Microbiology and Biotechnology Letters
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• v.19 no.1
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• pp.64-69
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• 1991

- The effects of sodium acetate on the production of $\gamma$-linolenic acid (GLA) and the secretion of the mycelial lipid into the culture medium with noninnic surfactants were studied with Mucor sp. KCTC 8405P. In the addition of 2.0%) sodium acetate to the basal medium, dry cell weight and total lipid content were increased from 7.8 g/l and 2.46 g/l to 16.0 g/1 and 4.77 g/l, but GLA content was decreased from 18.6% to 13.85%. The growth of Mucor sp. KCTC 8405P was greatly dependent on both the initial pH and the concentration of sodium acetate of culture medium, which was considered as the results of the formation of acetic acid because the fungal growth was completely inhibited at the concentration of acetic acid higher than 22 mM. With the decrease of the oxygen supply, the cell growth, total lipid, and GLA content were sharply decreased in the presence of 2.0% sodium acetate. For the secretion of mycelial lipid into the culture medium, the effects of the various nonionic surfactants were examined. In the addition of 0.5% Tween 80 or Span 80 to the basal medium, 194 mg/l or 263 mg/l of GLA was obtained in the culture medium.

• Applied Chemistry for Engineering
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• v.30 no.4
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• pp.453-459
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• 2019

In this study, the influence factors on the stability of the O/W (oil in water) emulsions prepared with coconut oil and the nonionic mixed surfactant (Tween 80-Span 80) were evaluated. The concentration and HLB value of the nonionic mixed surfactant, and the degree of agitation were used as manufacture factors. The stability of prepared O/W emulsions were measured with the mean droplet size, zeta-potential, emulsion stability index (ESI), and thermal instability index (TII). The mean droplet size of the prepared O/W emulsions was from 100 to 200 nm. As the concentration of mixed surfactant and the homogenization speed increased, the droplet sizes decreased, while the zeta-potential values increased. The effect of HLB values increased in the order of 6.0, 10.0 and 8.0, and at the HLB value of 8 the smallest mean droplet size as 120 nm was obtained whereas the largest value of the zeta-potential between 10 and 60 mV. From the results of ESI and TII, the stability of prepared O/W emulsions increased in order of 6.0, 10.0 and 8.0 of HLB values, and ESI and TII values were above 80% and below 20% respectively at HLB value of 8.0.

• Journal of Korean Society of Steel Construction
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• v.19 no.6
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• pp.737-749
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• 2007

Flexural design of double composite box girder over the interior pier for three-span continuous bridge was performed by the LRFD method. The maximum span length of the continuous bridge ranged from 80m to 120m and the relative ratio of the span length was assumed to be 1:1.25:1. The girder section was designed for the strength limit state and service limit state with additional design check for constructibility. Before the bottom concrete and compression flange showed a complete composite action, the buckling of lower compression flange was checked. The flexural stiffness and flexural resistance characteristics for the section and for the constituent members such as tension flange, compression flange, and web were analyzed for different thicknesses of the bottom concrete on top of the compression flange. The effect of the distribution ratio of steel between the top and bottom flanges was investigated by analyzing ductility behavior and stress distribution through the girder's depth for several different relative area ratios of steel between the top and bottom flanges. It was found that a total amount of 15% of steel can be saved by applying the double composite system compared with that of the conventional composite system.

• Journal of Korean Society of Steel Construction
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• v.24 no.3
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• pp.337-348
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• 2012

This study investigated the characteristics of bifurcation and the instability due to the initial imperfection of the space truss, which is sensitive to the initial conditions, and the calculated buckling load by the analysis of Eigen-values and the determinant of tangential stiffness. A two-free nodes model, a star dome, and a three-ring dome model were selected as case studies in order to examine the unstable phenomenon due to the sensitivity to Eigen mode, and the influence of the rise-span ratio and the load parameter on the buckling load were analyzed. The sensitivity to the imperfection of the two-free nodes model changed the critical path after reaching the limit point through the bifurcation mode, and the buckling load level was reduced by the increase in the amount of imperfection. The two sensitive buckling patterns for the model can be explained by investigating the displaced position of the free node, and the asymmetric Eigen mode was a major influence on the unstable behavior due to the initial imperfection. The sensitive mode was similar to the in-extensional mechanism basis of the simplified model. Since the rise-span ratio was higher, the effect of local buckling is more prominent than the global buckling in the star dome, and bifurcation on the equilibrium path occurring as the value of the load parameter was higher. Additionally, the buckling load levels of the star dome and the three-ring model were about 50-70% and 80-90% of the limit point, respectively.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.40-47
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• 2018

Porous walkway blocks are constructed for the purpose already, but reserved water is easily consumed due to the bigger permeability than necessary. Furthermore, porous structure reduces the strength of blocks, which resulting cracking and settlements in walkways. In this study, we suggested a solution for given problems by determination for the location of minimum principal stress in walkway blocks against moving foot loads in order to design and verifying the determined location of minimum principal stress. An optimum design with a verification example for determined location of minimum principal stress have been presented in a two dimensional Block member on elastic foundation for pedestrian walkway for reserving water inside. The minimum value for sum of shear forces is found when ${\times}1$ is 58.58 mm(30% of total span, 200mm), while the minimum deformation is located at ${\times}2=80mm$(70% of total span, 200 mm). In a modified model, When moving boundary condition(walkway foot loads) is located at ${\times}1$(=0 mm), the location of minimum principal stresses is found at 168 mm( 84% of span, 200 mm), in which the stress concentration due to the foot load is modeled as two layers of distributed loads(reactions of foundation modeled as springs). Consequently, zero deformed reservoirs for rainwater on the neutral axis (${\times}2=167mm$) has been determined in the modified model with three dimensional FEM analysis verifications.

• Korean Journal of Agricultural Science
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• v.39 no.2
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• pp.271-277
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• 2012

Dimensions, operation conditions and improvement items for round roof windows were investigated in arch shape single-span plastic greenhouse with roof vents, and natural ventilation performance was analyzed based on the ventilation theory. Diameter of round roof windows was mostly 60 cm, and chimney height projected on roof was average 30 cm. Installation space was mostly 5 to 6 m but farmhouse of 10 m and over was 16.7% also. A round roof window which has 60 cm diameter was installed to 6 m space generally and 80 cm diameter was installed to 10 m space, but correct standards did not exist. There were a lot of opinions that ventilation effect of round roof windows is fairly good and user satisfaction is generally excellent. It is problem that there is few effects in summer and that vinyl around each vent tears well and rainwater leaks, and improvement hope item required development of automatic control system. In the wind speed of 0.3 m/s, it was estimated that natural ventilation rates were 0.69, 0.55, 0.50 and 0.48 volumes per minute in case of 2, 4, 6 and 8 m installation space for round roof windows, respectively. It was analyzed that the ratio of ventilation due to buoyancy out of total ventilation were 65.2, 41.9, 29.9 and 22.8% in case of 2, 4, 6 and 8m installation space, respectively. By the round roof windows installed at space of 6 m, ventilation rate was estimated to 0.5 volumes per minute, and we can expect the increase in ventilation rate of 30%. In order to meet the recommended ventilation rate for summer season, we have to install the round roof windows at space of 1 to 2 m. However, it is difficult to apply those installation space because of falling productivity due to lower light transmittance as well as rising costs. It is estimated that the installation space of 6m is appropriate for spring or fall season. Therefore it is necessary to encourage installing the roof windows in single-span plastic greenhouses.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.9
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• pp.763-771
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• 2014

As a preliminary study on the spray behavior characteristics of emulsified fuel, the fuel properties (viscosity, surface tension, and density) and evaporation characteristics of a fuel droplet were investigated. The emulsified fuel was made by mixing diesel and $H_2O_2$. In addition, the macroscopic spray behavior characteristics such as the spray penetrations and spray angles of the emulsified and diesel fuels were compared. The stirring condition of the emulsified fuel was a 9:1 mixture of the diesel fuel and the surfactant span 80. The mixing ratios for the hydrogen peroxide were set at EF2, EF12, EF22, EF32, EF42, EF52, EF62, EF72, EF82, and EF92. The injection pressures were set at 400, 600, 800, and 1000 bar. We found that as the mixing ratio of the hydrogen peroxide was increased from EF2 to EF52, the viscosity of the emulsified fuel increased. However, afterward, the viscosity of the emulsified fuel gradually decreased and approached the viscosity value of the diesel fuel. Therefore, generally oil-in-water emulsions were used for the hydrogen peroxide mixing ratios up to 52 (EF52), and water-in-oil emulsions were used for the hydrogen peroxide mixing ratios above 52. Finally, the spray behavior characteristics (spray penetration and spray angle) of the emulsified fuel were found to be almost independent of the mixing ratio.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.466-473
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• 2017

RC (Reinforced Concrete) member has varying service life due to varying diffusion characteristics with loading conditions even if it is exposed to constant exterior conditions. In the paper, quantitative parameters are obtained through adopting the previous results for effects of compressive, tensile, and cold joint on chloride diffusion in OPC (Ordinary Portland Cement) and GGBFS (Ground Granulated Blast Furnace Slag) concrete. Service life is evaluated in RC simple beam with 10.0m of span through increasing loading from self weight (2.5kN/m) to the loading to cracking moment (5.5kN/m). In OPC concrete without cold joint, service life changes to 89.4% for tensile region and 101% for compressive region with loadings while GGBFS concrete has 80.0% and 106%, respectively. For cold joint area, GGBFS concrete shows much reduced service life to 82~80% in compressive region and 69~61% in tensile region, which is caused by the lower diffusion in normal condition but relatively higher increasing cold joint effect than OPC concrete.