• Korean Journal of Microbiology
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• v.34 no.3
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• pp.144-148
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• 1998

Soil microorganisms including bacteria, fungi, and actinomycetes were seasonally isolated at depths (0.5~2, $10{\pm}1$, $50{\pm}1cm$) of field. The frequency of microbial isolates was employed for the determination of microbial population (CFU/g dry soil) and distribution ratio (%) in soil. Both bacteria (24-fold) and actinomycetes (7-fold) exhibited the biggest change at the depth of $50{\pm}1cm$, whereas fungi showed the maximum (13-fold) at $10{\pm}1cm$. On the whole, the bacterial population was high in spring soil, fungi in winter, and actinomycetes in autumn. Soil microorganisms also exhibited the seasonal variation on their distribution ratio (%). The maximum distribution ratio (85.7%) of bacteria was observed at the depth of $50{\pm}1cm$ in spring, whereas bacteria showed the minimum (35.2%) at the depth of $10{\pm}1cm$ in spring. The maximum distribution ratio (23.0%) of fungi was found at the depth of $50{\pm}1cm$ in spring, whereas its minimum (0.5%) at the depth of $10{\pm}1cm$ in spring. Actinomycetes exhibited the maximum distribution ratio (45.2%) at the depth of $10{\pm}1cm$ in spring, whereas its minimum (12.2%) was showed at the depth of $50{\pm}1cm$ in spring.

• Journal of the Korean Wood Science and Technology
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• v.26 no.4
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• pp.6-12
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• 1998

Test results of domestic softwood lumber were presented to examine the notch effect of beams and compare to present AIJ(Architecture Institute of Japan) formula in notched wood member especially positioned in bottom side (tension side) of a beam. Notched lumber was tested under following condition : each specimen supported simply, and subjected to third-point loading at points of 1/3 of the span length. Notch was located opposite side to loading direction and notch depth were 1/6, 1/4, 1/3 of beam depth. Deflection and load were measured by digital dial guage each in 25kgf increment. Bending test results were as follows; Mpro/Mmax range (proportional and maxium bending moment ratio in notched beam) was 0.5 - 0.65. It was considered that maxium bending moment was about 1.5 times to proportional bending moment in notched beam and showed same tendency in the test result of ordinary wood specimens. AU standard formula for the tension side notch, Mmat = 0.6 ${\times}$ (Zo $\sigma$), the constant 0.6 was suitble for notch ratio(notch depth to beam depth) 1/6, but this ratio for 1/4, and 1/3 was not. So it is preferable to accept smaller value than 0.6 for notch ratio more than 1/3. These experiment results showed critical effect in tension side notched wood beam especially in greater than notch ratio 1.3 of wood beam. From the above results, it is recommened to revise design formula adoptable to domestic wood constructon member with tension side notched member.

• Geomechanics and Engineering
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• v.36 no.4
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• pp.367-380
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• 2024

Investigations has shown that the correct estimation of the effective amplification period is as important as the amplification value itself. It gets more important in 2D basins. This study presents a quantitative coefficient for consideration of the nonlinearity effect in terms of amplification value and the shift in its period which is missing or ineffectively considered in the previous studies. To attain this goal, by the application of a time domain fully nonlinear method, the deviation of the more common equivalent linear results from the basin nonlinear behavior under strong ground motions is investigated quantitatively. Also, despite the increase in the damping ratio, the possibility of the increase in the amplification due to the increase in motion strength is shown. To make the results useful in engineering practice, by introducing nonlinearity ratio, the effect of the nonlinearity is quantitatively estimated for two soft and stiff clayey basins with three different depths under a set of motions scaled to two target spectrum. Results show that at the 100 m depth soft clayey basin, while the nonlinearity ratio shows a 35% deviation at the basin edge part under DD1 motion level, its effect moves to the central part with 20% effect under DD3 motion level. By the increase in depth to 150 m, the results show a decrease in the overall effect of the nonlinear behavior for both clay types. At this depth, the nonlinearity ratio gives a 30% and 17% difference on a limited distance from outcrop at the soft clayey basin under DD1 and DD3 motion levels, respectively. At the 30 m depth basins, the nonlinearity ratio shows up to 25% difference for different cases. The presented ratio would be introduced as nonlinearity coefficients for consideration of the nonlinearity effects in the codes. The presented quantitative margins will help the designer to have a better understanding of the amplification period change because of nonlinearity over 2D basin surface.

• Architectural research
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• v.4 no.1
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• pp.39-44
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• 2002

Recently, the coal-ash production has been increased by increase of consumption of electric power. So it is important to secure a reclaimed land from pollution and develop practical application of coal ash. This is an experimental study to compare and analyze the properties of concrete using high volume of coal ash (including fly ash and bottom ash) as a part of fine aggregate. For this purpose, the mix proportions of concrete according to replacement ratio of coal ash (10, 20, 35, 50%) were selected. And then air content, slump, setting time, bleeding content, chloride content, compressive strength and carbonation test were performed. According to test results, it was found that the bleeding content of concrete using the coal ash decreased according to increase of replacement ratio. And the chloride content of concrete using the bottom ash as a part of fine aggregate increased as the replacement ratio of bottom ash increased, but it is satisfied with the total chloride content of concrete recommended by KCI - $0.3kg/m^3$ below. Also, the compressive strength of concrete using the bottom ash was similar to that of plain concrete(BA 0) after 28days of curing and the carbonation depth of concrete increased as the replacement ratio increased. However, the carbonation depth of concrete using the fly ash decreased as the replacement ratio of fly ash increased.

• Computers and Concrete
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• v.20 no.2
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• pp.129-143
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• 2017

Seismic design of reinforced concrete (RC) structures requires a certain minimum level of flexural ductility. For example, Eurocode EN1998-1 directly specifies a minimum flexural ductility for RC beams, while Chinese code GB50011 limits the equivalent rectangular stress block depth ratio at peak resisting moment to achieve a certain nominal minimum flexural ductility indirectly. Although confinement is effective in improving the ductility of RC beams, most design codes do not provide any guidelines due to the lack of a suitable theory. In this study, the confinement for desirable flexural ductility performance of both normal- and high-strength concrete beams is evaluated based on a rigorous full-range moment-curvature analysis. An effective strategy is proposed for flexural ductility design of RC beams taking into account confinement. The key parameters considered include the maximum difference of tension and compression reinforcement ratios, and maximum neutral axis depth ratio at peak resisting moment. Empirical formulae and tables are then developed to provide guidelines accordingly.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.385-388
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• 1999

This study is to investigate experimentally the shear capacity of high-strength reinforced concrete beams subjected to monotonic loading. Nine reinforced concrete beams using high strength concrete $(f'c=380kg/\textrm{cm}^2)$ are tested to determine their diagonal cracking and ultimate shear capacity. The main variables are shear span-depth ratio a/d=1.5, 2.5, 3.5, and shear reinforcement ratio. All specimens are 170mm wide and have a total depth of 300mm. The test results indicate that ACI 318-95(b) Code for shear capacity gave closest agrement with the exsprimental results. The beams with a shear spear-depth ratio 1.5 and 2.5. ACI 318-95 Code underestimates shear strength carried by vertical shear reinforcements.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.501-506
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• 2002

The unbonded prestressed concrete(PSC) members exhibit very different structural behavior from that of bonded PSC members because of having different tendon stress increment. Recently, AASHTO changed the provision of ultimate tendon stress with unbonded tendons, because some researches tried to improve the provision of ultimate tendon stress with unbonded tendons. The purpose of the present study is to compare various Codes with the ultimate failure stresses of prestressing(PS) steels for the unbonded PSC members. To this end, Some national Codes have been collected and analyzed. A series of major influencing variables have been included in the analysis. It was found that the span-depth ratio, neutral axis depth-effective depth ratio, concrete compressive strength, effective prestress, and prestressing steel ratio have great influence on the ultimate failure stress of PS steel in unbonded PSC members. The Comparison indicates that existing formulas including ACI and domestic Code's equations shows some unwarranties. The present study allows more realistic analysis and design of prestressed concrete structures with internal unbonded tendons.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.4
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• pp.104-116
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• 1998

This paper provides a review of the performance for SM45C using the CNC lathe. Under the constant cutting area, the tool wear for large feed rate is more than the small feed rate, and the progress goes more rapidly as the cutting speed is increased. This is caused by the friction between the workpiece and the bite. The average cutting force increases as the feedrate increases, and decreases as the cutting speed increases. This is because the effective rake/shear angle becomes smaller as the feedrate becomes larger. The higher is the cutting speed and the aspect ratio (the ratio for depth of cut to feedrate), the lower is the cutting force and the surface roughness. Also, for the optimal selection of the cutting conditions, many experimental graphical data were obtained. That is, the cutting force, the tool life, and the surface roughness were measured and investigated as the depth of cut and the feedrate changed. And the size effect was examined as the depth of the cut varied.

• KCI Concrete Journal
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• v.11 no.3
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• pp.211-221
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• 1999

A method to determine the fracture energy of concrete is investigated. The fracture energy may be calculated from the area under the complete load-deflection curve which can be obtained from a stable three-point bend test. Several series of concrete beams have been tested. The Present experimental study indicates that the fracture energy decreases as the initial notch-to-beam depth ratio increases Some problems to be observed to employ the three-point bend method are discussed. The appropriate ratio of initial notch-to-beam depth to determine the fracture energy of concrete is found to be 0.5. It is also found that the influence of the self-weight of a beam to the fracture energy is very small A simple and accurate formula to predict the fracture energy of concrete is proposed.

• Journal of The Korean Society of Agricultural Engineers
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• v.47 no.5
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• pp.63-71
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• 2005

In-situ soil remediation mechanism through the vertical drains (VDs) is analyzed with numerical model as the error and complementary error function. Results from in-situ test and analysis indicate that the contaminant concentration ratio as initial one ( C/$C_0$) increases as the radius ratio ( r/R) increases from the injection well, and also increases as the depth ratio ( z/ H) increases from the top of contaminated area. The elapse time needed to attain $50\%$ and $90\%$ clean up level ($ t_{50},\;t_{90}$) increases as the radius ratio ( r/R) and the depth ratio ( z/ H) increase. As above results, the procedure of soil flushing in contaminated area using vertical drains makes progress from the top of injection well to the bottom of extraction well.