• Earthquakes and Structures
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• 제23권6호
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• pp.527-534
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• 2022

EDCC (Eco-Friendly Ductile Cementitious Composites) is a recently created class of engineered cementitious composites that exhibit extremely high ductility and elastoplastic behavior under pure tension. EDCC contains reduced amounts of cement and very large volumes of fly ash. Due to these properties, EDCC has become one of the solutions to use in seismic upgrading. This paper discloses previous studies and research that discussed the seismic upgrading of unreinforced, non-grouted, unconfined, and non-load bearing masonry walls which are called URM infill walls using the EDCC technique. URM infill wall is one of the weak links in the building structure to withstand the earthquake waves, as the brittle behavior of the URM infill walls behaves poorly during seismic events. The purpose of this study is to fill a knowledge gap about the theoretical and experimental ways to use the EDCC in URM infill walls. The findings reflect the ability of the EDCC to change the behavior from brittle to ductile to a certain percentage behavior, increasing the overall drift before collapse as it increases the energy dissipation, and resists significant shaking under extensive levels with various types and intensities.

• Steel and Composite Structures
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• 제42권1호
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• pp.123-137
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• 2022

The fundamental period (FP) is one of the most critical parameters for the seismic design of structures. In the reinforced concrete (RC) infilled frame, the infill walls significantly affect the FP because they change the stiffness and mass of the structure. Although several formulas have been proposed for estimating the FP of the RC infilled frame, they are often associated with high bias and variance. In this study, an efficient soft computing model, namely the group method of data handling (GMDH), is proposed to predict the FP of regular RC infilled frames. For this purpose, 4026 data sets are obtained from the open literature, and the quality of the database is examined and evaluated in detail. Based on the cleaning database, several GMDH models are constructed and the best prediction model, which considers the height of the building, the span length, the opening percentage, and the infill wall stiffness as the input variables for predicting the FP of regular RC infilled frames, is chosen. The performance of the proposed GMDH model is further underscored through comparison of its FP predictions with those of existing design codes and empirical models. The accuracy of the proposed GMDH model is proven to be superior to others. Finally, explicit formulas and a graphical user-friendly interface (GUI) tool are developed to apply the GMDH model for practical use. They can provide a rapid prediction and design for the FP of regular RC infilled frames.

• Structural Engineering and Mechanics
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• 제88권5호
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• pp.501-519
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• 2023

This paper introduces a new hybrid structural connection joint that combines shear walls with section steel beams, fundamentally resolving the construction complexity issue of requiring pre-embedded connectors in the connection between shear walls and steel beams. Initially, a quasi-static loading scheme with load-deformation dual control was employed to conduct low-cycle repeated loading experiments on five new connection joints. Data was acquired using displacement and strain gauges to compare the energy dissipation coefficients of each specimen. The destruction process of the new connection joints was meticulously observed and recorded, delineating it into three stages. Hysteresis curves and skeleton curves of the joint specimens were plotted based on experimental results, summarizing the energy dissipation performance of the joints. It's noteworthy that the addition of shear walls led to an approximate 17% increase in the energy dissipation coefficient. The energy dissipation coefficients of dog-bone-shaped connection joints with shear walls and cover plates reached 2.043 and 2.059, respectively, exhibiting the most comprehensive hysteresis curves. Additionally, the impact of laminated steel plates covering composite concrete floors on the stiffness of semi-rigid joint ends under excessive stretching should not be disregarded. A comparison with finite element analysis results yielded an error of merely 2.2%, offering substantial evidence for the wide-ranging application prospects of this innovative joint in seismic performance.

• Nuclear Engineering and Technology
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• 제55권10호
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• pp.3860-3865
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• 2023

A metallic microcell UO₂ pellet has a microstructure where a metal wall is connected to overcome the low thermal conductivity of the UO₂ fuel pellet. It has been verified that metallic microcell fuel pellets provide an impressive reduction of the fuel centerline temperature through a Halden irradiation test. However, it is difficult to predict the effective thermal conductivity of these pellets and researchers have had to rely on measurement and use of the finite element method. In this study, we designed a unit microcell model using a thermal resistance circuit to calculate the effective thermal conductivity on the basis of the microstructure characteristics by using the aspect ratio and compared the results with those of reported metallic UO₂ microcell pellets. In particular, using the thermal conductivity calculated by our model, the fuel centerline temperature of Cr microcell pellets on the 5th day of the Halden irradiation test was predicted within 6% error from the measured value.

• Corrosion Science and Technology
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• 제23권2호
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• pp.139-144
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• 2024

Recently, due to the rapid spread and continuation of COVID-19, customer demand for health and hygiene has increased, requiring the development of new products that express antiviral and antibacterial properties. In particular, viruses are much smaller in size than bacteria and have a fast propagation speed, making it difficult to kill. POSCO has developed eco-friendly PCM color coated steel sheets with excellent antiviral properties by introducing inorganic composite materials to the color coating layer on the surface of Zn-Al-Mg alloy plated steels. The virus is not only destroyed by adsorption of metal ions released from the surface of the coating film, but is also further promoted by the generation of reactive oxygen species by the reaction of metal ions and moisture. As a result of evaluating the developed products under the International Standard Evaluation Act, the microbicidal activity was 99.9% for viruses, and 99.99% for bacteria and 0% fungi. In particular, excellent results were also shown in the durability evaluation for life cycle of the product. The developed product was applied as a wall of school classrooms and toilets and ducts for building air conditioning, resulting in excellent results. Developed products are being applied for construction and home appliances to practice POSCO's corporate citizenship.

• 콘크리트학회논문집
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• 제27권5호
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• pp.541-549
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• 2015

본 논문에서는 고인성 시멘트 복합체(ECC)가 적용된 날개벽 요소의 면 접합방식에 따른 평가를 실시하였다. 또한 비내진상세를 갖는 RC 골조에 ECC날개벽 요소 보강하여 보강 유무에 따른 내진성능평가를 실시하였다. 면 접합 방법에 따른 거동 특성을 비교하기 위하여 2면 접합은 상 하부 보에 3면 접합은 상 하부 보 및 기둥에 접합하여 실험을 실시 하였다. 또한 비내진상세를 갖는 기존 구조체와의 일체로 거동하는 합성거동을 위해 3면 접합 방식으로 ECC날개벽 요소 보강을 실시하였다. ECC날개벽 요소 실험과 골조 실험은 점증되는 층간변위에 따라 2회씩 반복가력하여 실험을 진행하였다. 실험 결과 ECC 날개벽 요소 실험체의 경우 3면 접합이 2면 접합보다 우수한 내진성능 나타내었다. 각각의 실험체는 우수한 재료 특성으로 인하여 미세한 다수의 균열이 ECC날개벽 요소 전면에 폭넓게 분포하였다. 또한 보통 콘크리트와 달리 최대강도 이후 연성적인 거동을 나타내었으며, 이에 우수한 에너지소산능력을 나타내었다. ECC날개벽 요소를 보강한 실험체와 기존 골조에서는 ECC날개벽 요소 보강에 따른 최대강도 이후 연성적인 거동을 나타내었다. 이에 따라 에너지소산능력이 증가하였으며, 강성저하 또한 완만한 곡선을 나타내며 기존 골조보다 우수한 내진특성을 나타내었다. 이에 ECC 날개벽 요소의 보강이 비내진상세를 갖는 구조체에 우수한 내진 특성을 부여하는 판단된다.

• 한국해안·해양공학회논문집
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• 제32권3호
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• pp.180-201
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• 2020

유한길이의 혼성방파제 선단에서 발생되는 회절파의 영향으로 방파제 길이를 따라 중복파고가 변동하고, 이로 인하여 케이슨에 작용하는 파압이 공간적으로 변동하며, 또한 케이슨의 활동거리가 상이한 사행피해가 발생한다는 것은 잘 알려져 있다. 제체에 작용파력의 공간적인 변동은 2차원적인 실험이나 수치해석으로서는 접근될 수 없는 문제이다. 본 연구는 olaFlow 모델을 적용하여 고천단의 사석마운드 상에 놓인 케이슨의 선단 주변에서 회절파의 발생과 배후역으로의 영향 및 제체에 작용하는 충격쇄파압을 포함한 파압의 공간적인 변동 등을 2차원 및 3차원수치기법으로 접근한다. 또한, 수치해석에서는 혼성방파제 주변에서 평균파고, 평균수평유속 및 평균난류운동에너지의 변동특성을 면밀히 분석·검토한다. 이로부터 동일한 입사파랑에 대해 케이슨에 작용하는 파압분포가 방파제의 길이에 따라 크게 변동하며, 2차원수치해석에서는 발생되지 않았든 충격쇄파압이 3차원수치해석에서는 발생되는 경우가 나타나고, 충격쇄파압의 발생 시 경우에 따라 기존의 설계조건보다 매우 큰 파압이 정수면 근방의 케이슨 전면 벽체에 작용되는 등의 중요한 결과를 확인할 수 있었다.

• Korean Chemical Engineering Research
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• 제55권4호
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• pp.456-466
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• 2017

이 연구는 교반볼밀을 이용한 금속기반 복합재 제조공정에 있어서 분쇄매체의 차이에 의한 입자형상의 변화를 관찰하고, 볼 거동의 DEM시뮬레이션을 행하였다. 교반볼밀에서 볼 거동의 3차원 시뮬레이션을 통해 분쇄메커니즘을 규명하기 위하여 분쇄매체의 힘, 운동에너지, 매체 운동속도 등을 계산하였다. 또한 복합재 제조를 위한 실험조건을 이전의 다른 볼밀에서에 같이 교반볼밀 회전속도를 변화시켰고, 볼 재질, 운동속도, 마찰계수 등도 동일한 조건으로 변화시키면서 투입되는 에너지의 변화량도 계산하였다. 교반볼밀의 회전속도가 증가함에 따라, 분쇄매체와 매체, 매체와 벽면, 그리고 매체와 교반기 사이의 충격에너지가 증가하는 것을 정량적으로 계산 할 수 있었다. 또한 같은 실험 조건에서 입자형상 변화를 명확하게 분석 할 수 있었으며, 볼 거동이 입자형상 변화에 매우 큰 영향을 미치는 것을 알 수 있었다.

• Restorative Dentistry and Endodontics
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• 제22권1호
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• pp.428-446
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• 1997

Restorative procedures can lead to weakening tooth due to reduction and alteration of tooth structure. It is essential to prevent fractures to conserve tooth. The resistance to fracture of the restored tooth may be influenced by many factors, among these are the cavity dimension and the physical properties of the restorative material. The placement of direct composite resin restorations has generally been found to have a strengthening effect on the prepared teeth. It is the purpose of this investigation to study the relationship between the cavity isthmus and the fracture resistance of a tooth in composite resin restorations. In this study, MO cavity was prepared on maxillary first premolar. Three dimensional finite element models were made by serial photographic method and isthmus(1/4, 1/3, 1/2 of intercuspal distance) were varied. Two types of model(B and R model) were developed. B model was assumed perfect bonding between the restoration and cavity wall and R model was left unfilled. A load of 500N was applied vertically at the first node from the lingual slope of the buccal cusp tip. This study analysed the displacement, 1 and 2 direction normal stress and strain with FEM software ABAQUS Version 5.2 and hardware IRIS 4D/310 VGX Work-station. The results were as follows : 1. Displacement of buccal cusp in R model occurred and increased as widening of the cavity, and displacement in B model was little and not influenced by cavity width. 2. There was a significant decrease of stress resulting in increase of fracture resistance in B model when compared with R model. 3. With the increase of the isthmus width, B model showed no change in the stress and strain. In R model, the stress and strain increased both in the area of buccal-pulpal line angle and the buccal side of marginal ridge, therefore the possibility of crack increased. 4. The stress and strain were distributed evenly on the tooth in B model, but in R model, were concentrated on the buccal side of the distal marginal ridge and buccal-pulpal line angle, therefore the possibility of fracture increased.

• Composites Research
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• 제19권5호
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• pp.28-33
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• 2006

본 논문에서는 카본 블랙, 탄소나노섬유, 탄소나노튜브를 혼합한 유리섬유/에폭시 복합재료 적층판의 복소 유전율과 그 특성이 전자파 흡수체 설계에 미치는 영향에 대한 연구를 수행하였다. 실험은 벡터회로망분석기와 7 mm 동축관을 이용하여 0.5 GHz$\sim$18 GHz의 주파수 영역에서 수행하였다. 실험결과는 복합재료의 복소 유전율이 첨가된 탄소나노소재의 함유율과 그 특성에 강하게 영향을 받는 것으로 나타났다. 복소 유전율의 실수부와 허수부는 탄소나노소재의 함유량에 따라 증가하지만, 탄소나노소재의 형태에 따라서 그 증가율이 모두 다르게 나타났다. 이러한 상이한 증가율은 단층형 흡수체의 설계에 있어서 두께에 영향을 준다. 이러한 영향은 단층형 흡수체를 설계하기 위한 복소 유전율의 해와 실험으로부터 얻은 세가지 종류의 복합재료의 복소 유전율을 함께 배치한 Cole-Cole 선도를 이용하여 평가되었다. 설계결과를 바탕으로 각각의 탄소나노소재를 이용하여 -10 dB의 흡수대역이 모두 3 GHz이면서 두께가 서로 다른 흡수체를 개발하였다.