• Geomechanics and Engineering
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• 제18권5호
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• pp.535-543
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• 2019

Building on/with expansive soils with no treatment brings complications. Compacted expansive soils specifically fall short in satisfying the minimum requirements for transport embankment infrastructures, requiring the adoption of hauled virgin mineral aggregates or a sustainable alternative. Use of hauled aggregates comes at a high carbon and economical cost. On average, every 9m high embankment built with quarried/hauled soils cost $12600MJ.m^{-2}$ Embodied Energy (EE). A prospect of using mixed cutting-arising expansive soils with industrial/domestic wastes can reduce the carbon cost and ease the pressure on landfills. The widespread use of recycled materials has been extensively limited due to concerns over their long-term performance, generally low shear strength and stiffness. In this contribution, hydromechanical properties of a waste tyre sand-sized rubber (a mixture of polybutadiene, polyisoprene, elastomers, and styrene-butadiene) and expansive silt is studied, allowing the short- and long-term behaviour of optimum compacted composites to be better established. The inclusion of tyre shred substantially decreased the swelling potential/pressure and modestly lowered the compression index. Silt-Tyre powder replacement lowered the bulk density, allowing construction of lighter reinforced earth structures. The shear strength and stiffness decreased on addition of tyre powder, yet the contribution of matric suction to the shear strength remained constant for tyre shred contents up to 20%. Reinforced soils adopted a ductile post-peak plastic behaviour with enhanced failure strain, offering the opportunity to build more flexible subgrades as recommended for expansive soils. Residual water content and tyre shred content are directly correlated; tyre-reinforced silt showed a greater capacity of water storage (than natural silts) and hence a sustainable solution to waterlogging and surficial flooding particularly in urban settings. Crushed fine tyre shred mixed with expansive silts/sands at 15 to 20 wt% appear to offer the maximum reduction in swelling-shrinking properties at minimum cracking, strength loss and enhanced compressibility expenses.

• 반도체디스플레이기술학회지
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• 제17권4호
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• pp.21-26
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• 2018

Recently, the emergence of 3D cameras, 3D scanners and various cameras including Lidar is expected to be applied to applications such as AR, VR, and autonomous mobile vehicles that deal with 3D data. In Particular, the 3D point cloud data consisting of tens to hundreds of thousands of 3D points is rapidly increased in capacity compared with 2D data, Efficient encoding / decoding technology for smooth service within a limited bandwidth, and efficient service provision technology for differentiating the area of interest and the surrounding area are needed. In this paper, we propose a new quality parameter considering characteristics of 3D point cloud instead of quality change based on assumed video codec in MPEG V-PCC used in 3D point cloud compression, 3D Grid division method and representation for selectively transmitting 3D point clouds according to user's area of interest, and propose a new 3D Manifesto. By using the proposed technique, it is possible to generate more bitrate images, and it is confirmed that the efficiency of network, decoder, and renderer can be increased while selectively transmitting as needed.

• 한국추진공학회지
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• 제23권1호
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• pp.52-60
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• 2019

본 연구에서는 수치해석을 활용하여 여러 개의 이젝터로 구성된 병렬형 이젝터의 성능과 구조에 대한 특성을 확인하였다. 병렬 이젝터의 설계는 단일 이젝터와 동일한 설계 변수(질량 흡입비, 압축비, 팽창비)를 사용하였다. 해석 결과에 의하면, 병렬형과 단일 이젝터의 작동 질량 흡입비의 비가 같을 경우에는 성능에 있어 큰 차이를 보이지 않았으나, 시스템의 크기가 작아지는 이점이 있음을 확인하였다. 또한, 동일 성능의 이젝터를 병렬로 배치하였을 때는 질량 흡입비가 단일 보다 감소하여 더 낮은 압력을 구현하는 것을 확인하였다. 해석 결과를 종합하면 병렬형 이젝터 성능은 단일 이젝터와 크게 다르지 않으나, 병렬형 이젝터 구성에 따라서는 크기와 작동에 이점이 있음을 확인하였다.

• Structural Engineering and Mechanics
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• 제70권1호
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• pp.13-31
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• 2019

A nonlinear finite element model (FEM) using ATENA-3D software to simulate the axially compressive behavior of circular steel tube confined concrete (CSTCC) columns infilled with ultra high performance concrete (UHPC) was presented in this paper. Some modifications to the material type "CC3DNonlinCementitious2User" of UHPC without and with the incorporation of steel fibers (UHPFRC) in compression and tension were adopted in FEM. The predictions of utimate strength and axial load versus axial strain curves obtained from FEM were in a good agreement with the test results of eighteen tested columns. Based on the results of FEM, the load distribution on the steel tube and the concrete core was derived for each modeled column. Furthermore, the effect of bonding between the steel tube and the concrete core was clarified by the change of friction coefficient in the material type "CC3DInterface" in FEM. The numerical results revealed that the increase in the friction coefficient leads to a greater contribution from the steel tube, a decrease in the ultimate load and an increase in the magnitude of the loss of load capacity. By comparing the results of FEM with experimental results, the appropriate friction coefficient between the steel tube and the concrete core was defined as 0.3 to 0.6. In addition to the numerical evaluation, eighteen analytical models for confined concrete in the literature were used to predict the peak confined strength to assess their suitability. To cope with CSTCC stub and intermediate columns, the equations for estimating the lateral confining stress and the equations for considering the slenderness in the selected models were proposed. It was found that all selected models except for EC2 (2004) gave a very good prediction. Among them, the model of Bing et al. (2001) was the best predictor.

• Computers and Concrete
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• 제27권4호
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• pp.333-341
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• 2021

Steel slag, an industrial reject from the steel rolling process, has been identified as one of the suitable, environmentally friendly materials for concrete production. Given that the coarse aggregate portion represents about 70% of concrete constituents, other economic approaches have been found in the use of alternative materials such as steel slag in concrete. Unfortunately, a standard framework for its application is still lacking. Therefore, this study proposed functional model equations for the determination of strength properties (compression and splitting tensile) of steel slag aggregate concrete (SSAC), using gene expression programming (GEP). The study, in the experimental phase, utilized steel slag as a partial replacement of crushed rock, in steps 20%, 40%, 60%, 80%, and 100%, respectively. The predictor variables included in the analysis were cement, sand, granite, steel slag, water/cement ratio, and curing regime (age). For the model development, 60-75% of the dataset was used as the training set, while the remaining data was used for testing the model. Empirical results illustrate that steel aggregate could be used up to 100% replacement of conventional aggregate, while also yielding comparable results as the latter. The GEP-based functional relations were tested statistically. The minimum absolute percentage error (MAPE), and root mean square error (RMSE) for compressive strength are 6.9 and 1.4, and 12.52 and 0.91 for the train and test datasets, respectively. With the consistency of both the training and testing datasets, the model has shown a strong capacity to predict the strength properties of SSAC. The results showed that the proposed model equations are reliably suitable for estimating SSAC strength properties. The GEP-based formula is relatively simple and useful for pre-design applications.

• 한국지반신소재학회논문집
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• 제18권3호
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• pp.101-112
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• 2019

그라우팅 공법은 연약지반의 보강과 방수, 부등침하로 손상된 구조물의 지지력을 향상시킨다. 본 연구는 보강섬유와 고로슬래그 미분말을 이용하여 그라우트재의 압축강도와 차수를 향상시키는데 있다. 이와 관련하여 본 연구에서는 고로슬래그 미분말의 비율이 높은(50% 이상) 시료에 대해 일축압축시험을 수행하였다. Mpa또한 탄소섬유와 아라미드 섬유를 비교하기 위하여 0, 0.5, 1.0%로 증가시켜 실험하였다. 탄소섬유 및 아라미드 섬유 함유량이 증가함에 따라 일축압축강도가 증가하였고 이는 그라우트재 내에 섬유에 의한 가교작용이 일축압축강도를 증가시키는 경향을 확인하였다. 또한 아라미드 섬유로 보강된 그라우트재에서 탄소섬유로 보강된 그라우트재 보다 일축압축강도가 약 10%이상 증가된 것을 확인하였다.

• 한국지반신소재학회논문집
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• 제20권4호
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• pp.33-41
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• 2021

장석은 석영과 더불어 국내에서 산출빈도가 가장 높은 광물이나 유리, 도료 등의 제조에 제한적인 이용을 제외하면 물질적 특성과 용도 개발에 대한 연구는 거의 이루어지지 않아 잠재적 가치가 매우 낮게 평가되고 있다. 본 논문에서는 다공성 구조를 특징으로 하는 장석의 재료특성과 열적, 기계적, 화학적, 경량화 활성기법을 적용하여 반응성 개선 특성을 분석하였다. 풍화된 장석의 표면에서 관찰되는 공동의 구조적 특징을 살펴보면 공동들의 배열이 불규칙하게 분포하고 있으며, 공동끼리는 서로 연결되어 있다. 이러한 풍화된 장석의 표면에서 관찰되는 비정형의 연결된 공동으로 인하여 풍화된 장석은 반응면적이 확대되며 시멘트와의 결합재료로서 반응성이 높은 포졸란 재료 역할을 하는 것으로 판단된다. 다공성 장석의 기능성을 향상시키기 위하여 열적, 기계적, 화학적 활성기법을 적용한 결과 양이온교환능력, 밀도, 일축압축강도 특성이 개선되었다. 이러한 다공성 특성에 의하여 풍화된 장석은 물리·화학적 특성이 우수한 친환경 건설재료로 활용이 가능할 것으로 판단된다.

• 한국지열·수열에너지학회논문집
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• 제18권3호
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• pp.7-18
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• 2022

Secondary batteries used in electric vehicles have a potential risk of ignition and explosion. Various safety measures are being taken to prevent these risks. A numerical study was performed using a computational fluid dynamics code on the cases where pressure relief vents that can reduce the blast overpressures of batteries were installed in the through-compression test room, short-circuit drop test room, combustion test room, and immersion test room in facilities rleated to battery used in electric vehicles. This study was conducted using the weight of TNT equivalent to the energy release from the battery, where the the thermal runaway energy was set to 324,000 kJ for the capacity of the lithium-ion battery was 90 kWh and the state of charge (SOC) of the battery of 100%. The explosion energy of TNT (△H_TNT) generally has a range of 4,437 to 4,765 kJ/kg, and a value of 4,500 kJ/kg was thus used in this study. The dimensionless explosion efficiency coefficient was defined as 15% assuming the most unfavorable condition, and the TNT equivalent mass was calculated to be 11 kg. The internal explosion generated in a test room shows the very complex propagation behavior of blast waves. The shock wave generated after the explosion creates reflected shock waves on all inner surfaces. If the internally reflected shock waves are not effectively released to the outside, the overpressures inside are increased or maintained due to the continuous reflection and superposition from the inside for a long time. Blast simulations for internal explosion targeting four test rooms with pressure relief vents installed were herein conducted. It was found that that the maximum blast overpressure of 34.69 bar occurred on the rear wall of the immersion test room, and the smallest blast overpressure was calculated to be 3.58 bar on the side wall of the short-circuit drop test room.

• 한국전산구조공학회논문집
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• 제35권5호
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• pp.287-297
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• 2022

본 논문에서는 철계형상기억합금(Fe SMA) 스트립으로 능동구속된 콘크리트 기둥의 실험적, 해석적 연구결과를 제시한다. Fe SMA과 탄소섬유보강시트(CFRP)로 각각 구속된 콘크리트 공시체의 압축실험을 통해 형상기억합금 기반 능동구속기법의 효과성을 평가하였다. 실험결과, Fe SMA 스트립으로 구속된 콘크리트 공시체가 낮은 구속력에도 불구하고 CFRP 시트로 구속된 공시체에 비해 더 우수한 변형능력을 가지는 것으로 밝혀졌다. 실험을 통해 얻은 구속된 콘크리트의 압축거동 결과를 이용해 소성힌지 영역이 각각 Fe SMA 스트립과 CFRP 시트로 보강된 콘크리트 기둥의 유한요소모델을 구축하였다. 기존 수행된 콘크리트 기둥의 수평반복가력 실험결과를 바탕으로 구축된 기둥 모델을 검증하였고, 각각의 기둥 모델에 대한 수평반복가력 해석을 수행하였다. 해석결과, Fe SMA 스트립으로 보강된 콘크리트 기둥이 CFRP 시트로 보강된 기둥모델에 비해 변형, 에너지 소산능력 향상에 효과적임을 확인하였다.

• Steel and Composite Structures
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• 제42권4호
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• pp.539-552
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• 2022

Concentrically braced frames (CBFs) possess high stiffness and strength against lateral loads; however, they suffer from low energy absorption capacity against seismic loads due to the susceptibility of CBF diagonal elements to bucking under compression loading. To address this problem, in this study, an innovative damper was proposed and investigated experimentally and numerically. The proposed damper comprises main plates and includes a flange plate angled at θ and a trapezius-shaped web plate surrounded by the plate at the top and bottom sections. To investigate the damper behaviour, dampers with θ = 0°, 30°, 45°, 60°, and 90° were evaluated with different flange plate thicknesses of 10, 15, 20, 25 and 30 mm. Dampers with θ = 0° and 90° create rectangular-shaped and I-shaped shear links, respectively. The results indicate that the damper with θ = 30° exhibits better performance in terms of ultimate strength, stiffness, overstrength, and distribution stress over the damper as compared to dampers with other angles. The hysteresis curves of the dampers confirm that the proposed damper acts as a ductile fuse. Furthermore, the web and flange plates contribute to the shear resistance, with the flange carrying approximately 80% and 10% of the shear force for dampers with θ = 30° and 90°, respectively. Moreover, dampers that have a larger flange-plate shear strength than the shear strength of the web exhibit behaviours in linear and nonlinear zones. In addition, the over-strength obtained for the damper was greater than 1.5 (proposed by AISC for shear links). Relevant relationships are determined to predict and design the damper and the elements outside it.