• 한국건설순환자원학회논문집
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• 제7권3호
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• pp.210-215
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• 2019

비표면적이 큰 콘크리트 구조체의 균열의 경우 재료적인 거동(수화열 및 건조수축)으로 균열이 발생하기 쉽다. 최근 들어 섬유를 혼입함으로서 콘크리트의 강도 및 균열 저항성 개선에 대한 많은 연구가 진행 중인데 주로 압축강도 개선보다는 인장강도 개선을 통하여 재료적 균열에 대한 저항을 높이는 연구에 집중되고 있다. 본 연구에서는 셀룰로오즈 섬유를 슬러리형으로 제조하여 이를 혼입한 시멘트 모르타르의 작업성, 압축강도 및 휨강도를 평가하였으며, SEM 측정을 통하여 섬유재의 뽑힘특성을 평가하였다. CF 혼입률을 $0.5kg/m^3{\sim}1.0kg/m^3$으로 혼입할 경우, 휨강도를 크게 향상 시킬 수 있으며, 일반 플라스틱 섬유재와 달리 뽑힘 시 충분한 조도를 가지고 있음이 관측되었다.

• Geomechanics and Engineering
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• 제8권1호
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• pp.53-66
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• 2015

Plastic wastes, particularly polyethylene terephthalate (PET) generated from used bottled water constitute a worldwide environmental issue. Reusing the PET waste for geotechnical applications not only reduces environmental burdens of handling the waste, but also improves inherent engineering properties of soil. This paper investigated factors affecting shear strength improvement of PET-mixed residual soil. Four variables were considered: (i) plastic content; (ii) plastic slenderness ratio; (iii) plastic size; and (iv) soil particle size. A series of unconfined compression tests were performed to determine the optimum configurations for promoting the shear strength improvement. The results showed that the optimum slenderness ratio and PET content for shear strength improvement were 1:3 and 1.5%, respectively. Large PET pieces (i.e., $1.0cm^2$) were favorable for fine-grained residual soil, while small PET pieces (i.e., $0.5cm^2$) were favorable for coarse-grained residual soil. Higher shear strength improvement was obtained for PET-mixed coarse-grained residual soil (148%) than fine-grained residual soils (117%). The orientation of plastic pieces in soil and frictional resistance developed between soil particles and PET surface are two important factors affecting the shear strength performance of PET-mixed soil.

• 대한토목학회논문집
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• 제32권5D호
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• pp.483-492
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• 2012

슬립폼 공법에 있어서 초기경화시간은 콘크리트가 거푸집에서 안전하게 빠져나올 수 있는 굳기를 갖게 되는 콘크리트 타설 후 경화시간으로써 슬립폼 시스템의 상승속도를 결정하는 중요한 요소이다. 따라서 슬립폼 시스템의 안전성 확보와 콘크리트의 시공품질을 확보하도록 초기경화시간을 파악하는 기술이 필요하다. 본 논문에서는 초음파를 이용하는 기법 중 표면파 속도를 이용하여 콘크리트의 경화정도를 파악하여 초기경화시간을 추정함으로써 슬립폼 시스템의 상승 시기를 결정하는 연구를 수행하였다. 관입저항시험과 압축강도시험을 수행하여 콘크리트의 초기경화시간과 압축강도와의 관계를 규명하였고, 또한 압축강도와 표면파 속도와의 관계를 규명하기 위해 초음파시험을 동시에 수행하였다. 표면파 속도를 측정하기 위해 연속웨이블릿변환을 사용하였으며, 이때 수치해석을 통해 연속웨이블릿변환의 사용에 대한 타당성을 입증하였다. 이로부터 슬립폼 시스템의 상승에 요구되는 표면파 전파속도를 제안하였으며, 슬립폼 시스템의 축소모형실험을 수행하여 제안한 표면파 속도가 슬립폼 상승 시기를 결정하는데 사용될 수 있음을 입증하였다.

• 펄프종이기술
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• 제45권5호
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• pp.37-43
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• 2013

This study was focused on applying a new paper coating binder, vinyl acetate-ethylene(VAE) emulsion, with SB-latex and acrylic emulsion for paper coating application. VAE emulsion has a low monomer cost and is non-toxic chemical than conventional adhesive for paper coating such as styrene-butadiene latex( SB-latex) and acrylic emulsion. We conducted double coating in order to test VAE emulsion, which was applied on top surface only. The results showed that optical properties of the coated paper with VAE were similar with the SB-latex binders. In case of bonding strength, dry-pick of the coated paper with VAE showed almost same with other binders while wet-pick of the coated paper with VAE had a little bit lower strength than that with SB-latex.

• 콘크리트학회논문집
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• 제11권5호
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• pp.69-77
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• 1999

A spalling is defined as the damages of concrete exposed to high temperature during the fire by causing cracks and localized bursting of small pieces of concrete. It is reported that spalling is caused by the vapor pressure and polypropylene(PP) fiber has an important role in protecting from spalling. This paper is a study on the properties and spalling resistance of high-performance concrete with the kinds of aggregate and the contents of PP fiber. According to the experimental results, concrete contained no PP fiber take place in the form of the surface spalling and the failure of specimenns after fire test regardless of the kinds of aggregate. Concrete contained more than 0.05% of PP fiber with the aggregate of basalt does not take place the spalling, while the concrete using granite and limestone does the surface spalling. It is found that residual compressive strength after exposed at high temperature has 50~60% of its original strength. Although specimens after exposed at high temperature is cured at water for 28days, they do not recover their original strength.

• Geomechanics and Engineering
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• 제5권5호
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• pp.419-445
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• 2013

This paper presents an experimental study on the influence of principal stress direction and magnitude of intermediate principal stress on the undrained stress-strain-strength behaviors of Bangkok Clay. The results of torsional shear hollow cylinder and advanced triaxial tests with various principal stress directions and magnitudes of intermediate principal stress on undisturbed Bangkok Clay specimens are presented. The analysis of testing results include: (i) stress-strain and pore pressure behaviors, (ii) stiffness characteristics, and (iii) strength characteristics. The results assert clear evidences of anisotropic characteristics of Bangkok Clay at pre-failure and failure conditions. The magnitude of intermediate principal stress for plane-strain condition is also investigated. Both failure surface and plastic potential in deviatoric plane of Bangkok Clay are demonstrated to be isotropic and of circular shape which implies an associated flow rule. It is also observed that the shape of failure surface in deviatoric plane changes its size, while retaining its circular shape, with the change in direction of major principal stress. Concerning the behavior of Bangkok Clay found from this study, the discussions on the effects of employed constitutive modeling approach on the resulting numerical analysis are made.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2006년도 6th International Meeting on Information Display
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• pp.1640-1644
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• 2006

The first issue that should be overcome in copper process is its poor adhesive strength between pure copper film and glass substrate. In this study, defining the adhesive strength of pure copper film on various substrates and clarifying the key deposition parameters are presented for the investigation of copper process. First, using different kinds of surface plasma treatments were studied and the results showed that the adhesive strength was not improved even though the roughness of glass substrate surface was increased. Second, adding an adhesive layer between glass substrate and pure copper film was used to enhance the adhesion. Based on the data in the present paper, adopting copper alloy film as an adhesive layer can have capability preventing peeling problem in copper process. Besides, Cu/Cu alloy structure could be etched with the same etchant with better taper angle than the one with single layer of Cu. Unlike Cu/Mo structure, there is no residual problem for Cu/Cu alloy structure during etching process. Finally, this structure was examined in electrical test without significant difference in comparison with the conventional metal process.

• Steel and Composite Structures
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• 제26권5호
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• pp.583-594
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• 2018

Although a lot of experimental and analytical investigations have been carried out for steel bridge piers made of SS400 and SM490, the formulas available for SS400 and SM490 are not suitable for evaluating ultimate load and deformation capacities of steel bridge piers made of high strength steel (HSS) SM570. The effect of various parameters is investigated in this paper, including plate width-to-thickness ratio, column slenderness ratio and axial compression force ratio, on the ultimate load and deformation capacities of steel bridge box piers made of SM570 steel subjected to cyclic loading. The elasto-plastic behavior of the steel bridge piers under cyclic loads is simulated through plastic large deformation finite element analysis, in which a modified two-surface model (M2SM) including cyclic hardening is employed to trace the material nonlinearity. An extensive parametric study is conducted to study the influences of structural parameters on the ultimate load and deformation capacities. Based on these analytical investigations, new formulas for predicting ultimate load and deformation capacities of steel bridge piers made of SM570 are proposed. This study extends the ultimate load and deformation capacities evaluation of steel bridge piers from SS400, SM490 steels to SM570 steel, and provides some useful suggestions.

• 한국해양공학회지
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• 제35권2호
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• pp.131-140
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• 2021

The paper deals with comparative study of various surrogate models based approximate optimization in the structural design of the passive type deck support frame under design load conditions. The passive type deck support frame was devised to facilitate both transportation and installation of 20,000 ton class topside. Structural analysis was performed using the finite element method to evaluate the strength performance of the passive type deck support frame in its initial design stage. In the structural analysis, the strength performances were evaluated for various design load conditions. The optimum design problem based on surrogate model was formulated such that thickness sizing variables of main structure members were determined by minimizing the weight of the passive type deck support frame subject to the strength performance constraints. The surrogate models used in the approximate optimization were response surface method, Kriging model, and Chebyshev orthogonal polynomials. In the context of numerical performances, the solution results from approximate optimization were compared to actual non-approximate optimization. The response surface method among the surrogate models used in the approximate optimization showed the most appropriate optimum design results for the structure design of the passive type deck support frame.

• Advances in concrete construction
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• 제6권6호
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• pp.631-643
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• 2018

The focus of this paper is given to the investigation of mechanical properties of steel fibre reinforced self-compacting concrete after being exposed to fire. The research programme covered tests of two sets of beams: specimens subjected to fire and specimens not subjected to fire. The fire test was conducted in an environment mirroring one of possible real fire situations where concrete surface for an extended period of time is directly exposed to flames. Micro-cracking of concrete surface after tests was digitally catalogued. Compressive strength was tested on cube specimens. Flexural strength and equivalent flexural strength were tested according to RILEM specifications. Damages of specimens caused by spalling were assessed on a volumetric basis. A comparison of results of both sets of specimens was performed. Significant differences of all tested properties between two sets of specimens were noted and analysed. It was proved that the limit of proportionality method should not be used for testing fire damaged beams. Flexural characteristics of steel fibre reinforced self-compacting concrete were significantly influenced by fire. The influence of fire on properties of steel fibre reinforced self-compacting concrete was discussed.