• Journal of Korean Society of Steel Construction
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• v.24 no.6
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• pp.735-742
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• 2012

This paper presents the experimental results of axially loaded stub columns of slender steel hollow square section(SHS) strengthened with carbon fiber reinforced polymers(CFRP) sheets. 6 specimens were fabricated and the main parameters were: width-thickness ratio(b/t) and CFRP retrofitting. From the tests, it was observed that two sides would typically buckle outward and the other two sides would buckle inward. A maximum increase of 33% was achieved in axial-load capacity. Also, stiffness and ductility index(DI) were compared between unretrofitted specimens and retrofitted specimens. In the last section, a prediction formula of the ultimate strength developed using the experimental results is presented.

• Korean Journal of Soil Science and Fertilizer
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• v.8 no.1
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• pp.19-23
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• 1975

In order to find out the effect of long-term annual additions of organic matter on the physico-chemical properties of paddy soil, the soil with and without compost application has been analysed. 1. There was no significant difference in the particle size distribution between compost and uncompost treatment, however, hydraulic conductivity, sedimention volume were remarkedly increased in compost. 2. Bulk density and soil strength were decreased in organic matter additions, but porosity increased. 3. Relative to Atterberg Limits, liquid limit, plastic limit, and elastic index were increased in compost. 4. Aggregate size distribution was slightly increased in additions of organic matter. 5. Regarding to chemical properties, pH, organic matter content, C.E.C. and extractable cation were increased in organic matter additions.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.48 no.2
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• pp.56-60
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• 2016

Neutral or alkaline papermaking provides many advantages in paper strength and processing conditions. It also provides the opportunity of using calcium carbonate fillers in papermaking. These diverse advantages have made almost all paper machines of printing and writing papers run under neutral and alkaline conditions. On the other hand, linerboard machines, which use recycled papers as a raw material, are running under acid conditions using a rosin sizing system. Because the recycled raw materials used by the linerboard industry contain significant amounts of alkaline papers, the linerboard industry has an interest in the possibility of using the neutral or alkaline papermaking opportunity. In this study, the compatibility of the recycled linerboards under neutral or alkaline papermaking conditions was examined by recycling them under various pH conditions. The sizing degree of the papers recycled under neutral or alkaline was significantly lower than that of acid formed papers indicating that during the neutral or alkaline recycling process the rosin sized papers lost their sizing efficiency. Recycling of acid formed linerboards under neutral or alkaline conditions increased the amount of foam, and the foam contained substantial amount of solid materials derived from the acid sizing systems. Use of cationic polyelectrolytes including PEI and poly-DADMAC improved the sizing degree of the recycled papers under neutral and alkaline conditions. PEI decreased the foam generation as well while poly-DADMAC did not show any reducing effect of the foam. These results suggest that PEI forms coordinate bonds with rosin acid and precipitate them onto the surface of recycled fibers, while the reaction products between poly-DADMAC and rosin acid ions still remain water soluble under neutral or alkaline conditions.

• Geomechanics and Engineering
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• v.11 no.3
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• pp.345-359
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• 2016

In order to investigate the influence of the interfacial angel on failure characteristics and mechanism of combined coal-rock mass, 35 uniaxial/biaxial compressive simulation tests with 5 different interfacial angels of combined coal-rock samples were conducted by PFC2D software. The following conclusions are drawn: (1) The compressive strength and cohesion decrease with the increase of interfacial angle, which is defined as the angle between structure plane and the exterior normal of maximum principal plane, while the changes of elastic modulus and internal friction angle are not obvious; (2) The impact energy index $K_E$ decreases with the increase of interfacial angle, and the slip failure of the interface can be predicted based on whether the number of acoustic emission (AE) hits has multiple peaks or not; (3) There are four typical failure patterns for combined coal-rock samples including I (V-shaped shear failure of coal), II (single-fracture shear failure of coal), III (shear failure of rock and coal), and IV (slip rupture of interface); and (4) A positive correlation between interfacial angle and interface effect is shown obviously, and the interfacial angle can be divided into weak-influencing scope ($0-15^{\circ}$), moderate-influencing scope ($15-45^{\circ}$), and strong-influencing scope (> $45^{\circ}$), respectively. However, the confining pressure has a certain constraint effect on the interface effect.

• Steel and Composite Structures
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• v.29 no.1
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• pp.77-90
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• 2018

This paper presents a combined numerical, experimental, and theoretical study on the behavior of the concrete-filled double circular steel tubular (CFDT) stub columns under axial compressive loading. Four groups of stub column specimens were tested in this study to find out the effects of the concrete strength, steel ratio and diameter ratio on the mechanical behavior of CFDT stub columns. Nonlinear finite element (FE) models were also established to study the stresses of different components in the CFDT stub columns. The change of axial and transverse stresses in the internal and external steel tubes, as well as the change of axial stress in the concrete sandwich and concrete core, respectively, was thoroughly investigated for different CFDT stub columns with the same steel ratio. The influence of inner-to-outer diameter ratio and steel ratio on the ultimate bearing capacity of CFDT stub columns was identified, and a reasonable section configuration with proper inner-to-outer diameter ratio and steel ratio was proposed. Furthermore, a practical formula for predicting the ultimate bearing capacity was proposed based on the ultimate equilibrium principle. The predicted results showed satisfactory agreement with both experimental and numerical results, indicating that the proposed formula is applicable for design purposes.

• Structural Engineering and Mechanics
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• v.72 no.5
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• pp.631-642
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• 2019

The objective of the present study is to examine the flexural behavior of two-span post-tensioned lightweight aggregate concrete (LWAC) beams using unbonded tendons and the reliability of the design provisions of ACI 318-14 for such beams. The parameters investigated were the effective prestress and loading type, including the symmetrical top one-point, two third-point, and analogous uniform loading systems. The unbonded prestressing three-wire strands were arranged with a harped profile of variable eccentricity. The total length of the beam, measured between both strand anchorages, was 11000 mm. The test results were compared with those compiled from simply supported LWAC one-way members, wherever possible. The ultimate load capacity of the present beam specimens was evaluated by the collapse mechanism of the plasticity theorem and the nominal section moment strength calculated following the provision of the ACI 318-14. The test results showed that the two-span post-tensioned LWAC beams had lower stress increase (Δf_ps) in the unbonded tendons than the simply supported LWAC beams with a similar reinforcement index. The effect of the loading type on Δf_ps and displacement ductility was less significant for two-span beams than for the comparable simply supported beams. The design equations for Δf_ps and Δf_ps proposed by ACI 318-14 and Harajli are conservative for the present two-span post-tensioned LWAC beams, although the safety decreases for the two-span beam, compared to the ratios between experiments and predictions obtained from simply supported beams.

• Nutrition Research and Practice
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• v.7 no.5
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• pp.409-417
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• 2013

This study was performed to determine the effects of dietary calcium (Ca) intake, milk and dairy product intake, and serum vitamin D level on bone mineral density. The survey data from the 2008-2009 Korea National Health and Nutrition Examination Survey (KNHANES) for adults (3,819 males, 5,625 females) aged > 20 years were examined; osteoporosis was defined according to the standards for Asian populations (T-score < -2.5). The risk for osteoporosis significantly decreased as Ca intake increased; this effect persisted (quartile 4 vs. quartile 1 of Ca intake: odds ratio [OR] 0.66; 95% confidence interval [CI]: 0.50-0.87) even after adjustment for gender, age, and other factors (body mass index, serum vitamin D, menstruation, female hormone intake, menopausal status, and the number of days per week of muscular strength exercise). Additionally, the risk for osteoporosis significantly decreased as the Ca/P ratio increased (quartile 4 vs. quartile 1: OR 0.76; 95% CI: 0.58-0.98). The degree of risk was 0.96 (0.66-1.38) in those who consumed < 1 portion of milk or dairy products daily, and 0.71 (0.53-0.96) in those who consumed > 1 portion per day, compared with those who had zero intake. The risk for osteoporosis significantly decreased as the serum 25(OH) vitamin D level increased. From these results, we advocate an increase in Ca, milk, and dairy product intake, and that serum 25(OH) vitamin D levels be maintained within the normal range, for the maintenance of bone health and the prevention of osteoporosis in adults.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.47 no.5
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• pp.482-488
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• 2014

The study investigated the chemical composition, pH, and texture of salted jellyfish processed in Indonesia, Thailand, and China as a pilot study for processing the jellyfish Nemopilema nomurai, which occurs in Korean coastal waters. The 14 samples of salted jellyfish included processed umbrella and oral arms and consisted of 68.4-78.3 g/100 g moisture, 1.79-4.37 g/100 g crude protein, and 0.07-0.41 g/100 g crude lipid. The total amino acid content was 2.30-4.69 g/100 g and glycine accounted for 20.07-37.37% of the total amino acids. Salting jellyfish reduces the possibility of microbial growth and enhances the shelf life because the samples have a pH of 3.77-4.35, salinity of 18.53-24.02%, and lower water activity of 0.77-0.80. The lightness (L), redness (a), and yellowness (b) of the samples were 53.98-61.32, 1.76-6.26, and 14.08-29.0, respectively. The springiness, strength, and hardness of the salted jellyfish differed significantly among the products. The sample processed in Indonesia had the highest springiness. While the chemical composition, pH, water activity, and color differed significantly among the products, there were no significant effects of the country of manufacture. These results will enable the determination of quality index parameters for salted processed Nemopilema nomurai caught in Korean coastal.

• Polymer(Korea)
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• v.25 no.3
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• pp.441-449
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• 2001

Compatibilization of blends based on poly(phenylene ether) (PPE) and polyamide (PA) has been practiced with the incorporation of a copolymer formed by grafting polystyrene onto polybutadiene latex (g-BS) which is further functionalized with maleic anhydride (MAH) (g-BS*) to impart reactivity with amine groups of PA. The major focus has been placed on the effect of the various structural factors in g-BS8 on the phase morphology and mechanical performance of the blends. For the balance of impact strength and heat resistance, it was important to locate g-BS n particles inside of the PPE phase, which was accomplished by the proper control of the molecular weight and amount of PS in g-BS*. For g-BS*'s having constant molecular weight and amount of PS, the reduction of MAH content or increase of rubber particle size in g-BS* resulted in the increase of domain size and consequently loss in mechanical properties. Based on the comparison made with the conventional PPE/PA blend comprising MAH grafted PPE as a compatibilizer, it was confirmed that the comparable level of mechanical performance can be achieved by an appropriate g-BS* type material with improved whiteness index.

• Korean Journal of Materials Research
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• v.14 no.10
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• pp.713-718
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• 2004

To study the dynamic strain aging behavior of Zr-0.4Sn-1.5Nb-0.2Fe sample tube for nuclear fuel cladding in the range of pressurized water reactor (PWR) operation temperature, the tensile tests of the tube specimens, which had been finally heat-treated at $470^{\circ}C\;and\;510^{\circ}C$, had been carried out with the strain rate $1.67{\times}10^{-2}/s\;and\;8.33{\times}10^{-5}/s$ at the various temperatures from room temperature to $500^{\circ}C$. It was observed that the elongation of the specimens got shortened as the temperature increased from $200^{\circ}C\;to\;340^{\circ}C$. The specimens that were finally heat-treated at $470^{\circ}C$ showed a plateau more remarkably on the plot of yield strength-temperature than those heat-treated at $510^{\circ}C$. In the range of $310\sim400^{\circ}C$, the strain rate sensitivity of the specimens finally heat-treated at $510^{\circ}C$ was $30.4\%\sim33.7\%$ lower but the work hardening exponent index of the specimens was a little higher than that without dynamic strain aging effect.