• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.6
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• pp.63-71
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• 2015

The objective of the present study is to investigate how elevated temperature ranging from $100^{\circ}C$ to $800^{\circ}C$ as well as room temperature affects the variation of mechanical properties of high strength concrete ($over\;f_{ck}=60MPa\;grade$). In this experiment, specimens were exposed for a period of $2^{\circ}C/min$ to temperatures of $20^{\circ}C$, $100^{\circ}C$, $200^{\circ}C$, $300^{\circ}C$ $400^{\circ}C$, $500^{\circ}C$, $600^{\circ}C$, $700^{\circ}C$ and $800^{\circ}C$, respectively. Accordingly, the study investigated the fire resistance performance of high strength concrete mixed with composite fibers which composed with hybrid fibers and steel fibers. After cooling down to ambient temperature, the following basic mechanical properties were then evaluated and compared with reference values obtained prior to thermal exposure: (i) compressive strength in room temperature; (ii) residual compressive strength; (iii) Poisson's ratio; (iv) weight change; (v) SEM analysis & XRD analysis In addition, XRD and SEM Images analyses were performed to investigate chemical and physical characteristics of high strength concrete with composite fibers according to high temperature.

• Journal of the Earthquake Engineering Society of Korea
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• v.16 no.5
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• pp.13-21
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• 2012

In this study, the response modification factor for a RC IMRF is evaluated via pushover analysis, where 5-story structures were designed in accordance with KBC2009. The bending moment-curvature relationship for beams and columns was identified with a fiber model, and the bending moment-rotation relationship for beam-column joints was calculated using a simple and unified joint shear behavior model and the moment equilibrium relationship for the joint. The results of the pushover analysis showed that the strength of the structure was overestimated with negligence of the inelastic shear behavior of the beam-column joint, and that the average response modification factor for category C was 7.78 and the factor for category D was 3.64.

• Journal of the Korea Concrete Institute
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• v.23 no.6
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• pp.799-808
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• 2011

In this study, a standardized test method to analyze tensile properties of multi-directional GFRP plate was proposed. Presently, tensile strength test of FRP composite reinforced with isotropic and orthotropic fiber is standardized according to ISO standard. Also, even though many studies were performed on test method to analyze the dynamic properties, the properties of tensile strength for multi-directional GFRP plate were not clearly identified. Currently, the domestic test method in accordance with ASTM, which is applicable to unidirectional FRP plate, gave tensile test results greater than actual properties. Thus, in this study, GFRP tensile test was conducted using the method found to be commonly applicable to all standards based on literature review of domestic and international references. Then, anchorage length experiments were performed using the proposed tension test method to evaluate validity of the method. Finally, optimal anchorage length was estimated from the numerical analysis to propose the standardized tensile strength method for GFRP multi-directional composite evaluation.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.85-88
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• 2008

Performance evaluation of RC bridge piers repaired by CFRP has been investigated. For this purpose, simplified CFRP stress-strain relationship has been proposed and use is made of inelastic time-dependent element developed by authors. Static time-history analysis has been carried out for a RC bridge pier repaired with CFRP. Analytical predictions shows a relatively good correlation with experimental results. In addition, in case of dynamic time-history analysis, effect of the CFRP repair intervention on shear has been evaluated. Comparative analysis reveals that a repaired member produces increased characteristics due to the repair intervention and may affect the overall response of a whole structure. Moreover, effect of shear significantly affect strength, stiffness and displacement response of the pier. In all, It is believed that the present analytical model and scheme enable a healthy evaluation of strength, stiffness and displacement capacities of a RC bridge pier being damaged and repaired.

• Journal of Korean Association for Spatial Structures
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• v.10 no.4
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• pp.49-57
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• 2010

This study is the research appling the representative Displacement-Based Design which is the basic concept of Direct Displacement Based Design proposed by Chopra and Goel to original Reinforced Concrete structure and determining the thickness of retrofit Steel Jacket about the Maximum design ground acceleration, and developing the more improved Algorithm as well as program by the Retrofit Design method and Nonlinear analysis by the Performance design method before and after reinforcement appling the determined retrofit thickness. To predict the target displacement of retrofitted columns, a nonlinear analysis model of reinforced concrete columns has been developed to be based on the nonlinear fiber cross-sectional and segmental analysis model, and the seismic displacement level of retrofitted columns is estimated by two procedures, the direct displacement-based design method and the displacement coefficient method. In examples of seismic retrofit design, the current seismic improved design method gives good results in improvements of displacement levels and displacement ductilities of retrofitted columns.

• Steel and Composite Structures
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• v.18 no.3
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• pp.583-601
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• 2015

In the present study, the combined effects of thermal and mechanical loadings on the interlaminar shear stresses of both moderately thin and thick composite laminated beams are numerically analyzed. The finite element modelling of laminated composite beams and analysis of interlaminar stresses are performed using the commercially available software package MSC NASTRAN/PATRAN. The validity of the finite element analysis (FEA) is demonstrated by comparing the experimental test results obtained due to mechanical loadings under the influence of thermal environment with those derived using the present FEA. Various parametric studies are also performed to investigate the effect of thermal loading on interlaminar stresses generated in symmetric, anti-symmetric, asymmetric, unidirectional, cross-ply, and balanced composite laminated beams of different stacking sequences with identical mechanical loadings and various boundary conditions. It is shown that the elevated thermal environment lead to higher interlaminar shear stresses varying with the stacking sequence, length to thickness ratio, ply orientations under identical mechanical loading and boundary conditions of the composite laminated beams. It is realized that the magnitude of the interlaminar stresses along xz plane is always much higher than those of along yz plane irrespective of the ply-orientation, length to thickness ratios and boundary conditions of the composite laminated beams. It is also observed that the effect of thermal environment on the interlaminar shear stresses in carbon-epoxy fiber reinforced composite laminated beams are increasing in the order of symmetric cross-ply laminate, unidirectional laminate, asymmetric cross-ply laminate and anti-symmetric laminate. The interlaminar shear stresses are higher in thinner composite laminated beams compared to that in thicker composite laminated beams under all environmental temperatures irrespective of the laminate stacking sequence, ply-orientation and boundary conditions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.1-8
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• 2018

The object of this paper is to find the characteristics of fire proof materials through an analytical method and to suggest a proper approach for fire-proof design of reinforced concrete beam strengthened with fiber reinforced polymer (FRP). Heating tests for fire-proof materials were conducted and the thermal conductivities and specific heats of them were simulated through finite element analyses. In addition, a finite element analysis on the beam specimen strengthened with FRP under high temperature, which was conducted by previous researchers, was performed and the analytical result was compared with test result. And then the compatibility of the analytical approach was evaluated. Finally, the heat resistance characteristic of RC beam strengthened with FRP was analyzed by the proposed analytical method and the strength decrease of the beam due to the high temperature was evaluated. From the comparison with analytical and test result, it was found that the heat transfer from outside to inside through the fire-proof materials can be suitably simulated by using the proposed analytical approach.

• Korean Journal of Community Nutrition
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• v.17 no.1
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• pp.69-80
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• 2012

This study was conducted to examine the nutritional status, quality of diet and quality of life in postmenopausal women with mild climacteric symptoms based on their food group intake patterns. The data for nutritional status were obtained using 3-day records. Quality of diet was assessed by INQ, NAR, MAR, DDS, DVS, DQI-I. Climacteric symptoms were analyzed by the questionnaire of Kupperman's index and MENoL. The subjects were classified into the five groups, GMVDF, GMVdF, GMVDf, GMVdf, GmVDF according to their food group intake patterns. Analysis of nutrient intakes showed that the GMVDF group took significantly higher levels of kcal, carbohydrate, protein, fat, vitamin A, thiamin, riboflavin, folate, vitamin C, vitamin E, calcium, phosphorous, sodium, iron, zinc and fiber than GMVdf group did (p < 0.05). INQ of Ca and Fe appeared to be higher in GMVDF than in GMVdf groups (p < 0.05). Analysis of NARs showed that missing milk groups took lower riboflavin, Ca and P than other groups did as the same result with MAR (p < 0.05). Analysis of DDS and DQI showed that GMVdf group had the lowest quality of diet (p < 0.05); however, no difference was found on DVS. The GMVdf group showed the worst climacteric symptoms compared with those of the other groups (p < 0.05). However, we couldn't observe any differences in menopause-specific quality of life among the groups. In conclusion, it would be beneficial to meet all five food groups to increase the quality of diet and to reduce the climacteric symptoms in postmenopausal women.

• Analytical Science and Technology
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• v.13 no.1
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• pp.89-95
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• 2000

Three grades of activated carbon fibers (ACFs) were prepared from various precursors of plantic, synthetic, and mixed fabrics of viscose rayon and cotton. The ACFs an exhibited type I isotherms on the adsorption of nitrogen or argon. Micropore analysis revealed that the ACFs have uniform micropore size distribution in which their peak diameters were in the range of $5.6{\pm}0.3{\AA}$. The BET surface area of ACFs up to $1600m^2g^{-1}$ was proportional to the adsorption capacity of iodine. The BET values of the ACFs prepared were proportional to the burn-off degree of the products.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.4
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• pp.1-8
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• 2013

Constitutive modeling of constituent materials is very important for reinforced concrete (RC) frames. Cyclic constitutive behavior of unconfined concrete, confined concrete and reinforcing steel should be well defined in fiber-based discretization of RC sections. This study performs nonlinear dynamic analyses of RC frame structures to investigate the sensitivity of seismic behavior of such frames to different constitutive models of constituent materials. The study specifically attempts to examine confinement effects in concrete modeling and degrading effects in steel modeling, which substantially affects the monotonic, cyclic and seismic responses of RC members and frames. Based on the system level analysis, it is shown that the response of non-ductile frames is less sensitive to confined concrete models while the modeling of reinforcing steel is quite influential to the inelastic response of both non-ductile and ductile frames.