• Structural Engineering and Mechanics
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• 제91권6호
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• pp.583-589
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• 2024

Accurately predicting the strength of concrete is vital for ensuring the safety and durability of structures, thereby contributing to time and cost savings throughout the design and construction phases. The compressive strength of concrete is determined by various material factors, including the type of cement, composition ratios of concrete mixtures, curing time, and environmental conditions. While mix design establishes the proportions of each material for concrete, predicting strength before experimental measurement remains a challenging task. In this study, Abrams's law was chosen as a representative investigative approach to estimating concrete compressive strength. Abrams asserted that concrete compressive strength depends solely on the water-cement ratio and proposed a logarithmic linear relationship. However, Abrams's law is only applicable to concrete using cement as the sole binding material and may not be suitable for modern concrete mixtures. Therefore, this research aims to predict concrete compressive strength by applying various conventional regression analyses and machine learning methods. Six models were selected based on performance experiment data collected from various literature sources on different concrete mixtures. The models were assessed using Root Mean Squared Error (RMSE) and coefficient of determination (R²) to identify the optimal model.

• Nuclear Engineering and Technology
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• 제34권1호
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• pp.90-103
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• 2002

The thermal and mechanical properties of compacted bentonite and bentonite-sand mixture were collected from the literatures and compiled. The thermal conductivity of bentonite is found to increase almost linearly with increasing dry density and water content of the bentonite. The specific heat can also be expressed as a function of water ontent, and the coefficient of thermal expansion is almost independent on the dry density. The logarithm of unconfined compressive strength and Young’s modulus of elasticity increase linearly with increasing dry density, and in the case of constant dry density, it can be fitted to a second order polynomial of water content. Also the unconfined compressive strength and Young’s modulus of elasticity of the bentonite-sand mixture decreases with increasing sand content. The Poisson’s ratio remains constant at the dry density higher than 1.6 Mg/m$_3$, and the shear strength increases with increasing dry density.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.11-30
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• 2000

Structural properties of reinforced concrete, such as bond and shear strength, that depend on the tensile properties of concrete are much lower for high-strength concrete than would be expected based on relationships developed for normal-strength concretes. To determine the reason for this behavior, studies at the University of Kansas have addressed the effects of aggregate type, water-cementitious material ratio, and age on the mechanical and fracture properties of normal and high-strength concretes. The relationships between compressive strength, flexural strength, and fracture properties were studied. At the time of test, concrete ranged in age from 5 to 180 days. Water-cementitious material ratios ranged from 0.24 to 0.50, producing compressive strengths between 20 MPa(2, 920 psi) and 99 MPa(14, 320psi). Mixes contained either basalt or crushed limestone aggregate, with maximum sizes of 12mm(1/2in). or 19mm(3/4in). The tests demonstrate that the higher quality basalt coarse aggregate provides higher strengths in compression than limestone only for the high-strength concrete, but measurably higher strengths in flexure, and significantly higher fracture energies than the limestone coarse aggregate at all water-cementitious material ratios and ages. Compressive strength, water-cementitious material ratio, and age have no apparent relationship with fracture energy, which is principally governed by coarse aggregate properties. The peak bending stress in the fracture test is linearly related to flexural strength. Overall, as concrete strength increases, the amount of energy stored in the material at the peak tensile load increases, but the ability of the material to dissipate energy remains nearly constant. This suggests that, as higher strength cementitious materials are placed in service, the probability of nonductile failures will measurably increase. Both research and educational effort will be needed to develop strategies to limit the probability of brittle failures and inform the design community of the nature of the problems associated with high-strength concrete.

• International Journal of Concrete Structures and Materials
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• 제6권3호
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• pp.145-153
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• 2012

The aim of this study is to explore the possibility of re-cycling a waste material that is now produced in large quantities, while achieving an improvement of the mechanical properties and durability of the mortar. This study examines the mechanical properties and the durability parameters of mortars incorporating plastics bag wastes (PBW) as fine aggregate by substitution of a variable percentage of sand (10, 20, 30 and 40 %). The influence of the PBW on the, compressive and flexural strength, drying shrinkage, fire resistance, sulfuric acid attack and chloride diffusion coefficient of the different mortars, has been investigated and analyzed in comparison to the control mortar. The results showed that the use of PBW enabled to reduce by 18-23 % the compressive strength of mortars containing 10 and 20 % of waste respectively, which remains always close to the reference mortar (made without waste). The replacement of sand by PBW in mortar slows down the penetration of chloride ions, improves the behavior of mortars in acidic medium and improves the sensitivity to cracking. The results of this investigation consolidate the idea of the use of PBW in the field of construction.

• 한국방재학회 논문집
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• 제10권5호
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• pp.9-15
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• 2010

최근 사용이 늘어나고 있는 고강도 콘크리트는 화재에 취약하여 고열에 의해 내부 수증기압의 상승으로 폭렬 현상이 발생하게 된다. 이러한 폭렬 현상의 방지 방안으로 유기질 섬유를 이용한 방법이 가장 많이 연구되고 있지만 이 방법은 결국 화재 후 콘크리트의 강도 저하를 초래하게 된다. 따라서 본 연구는 포비성 Alkali-Silicates계 내화재를 피복하여 유기질 섬유를 적용한 경우와 폭렬 특성 및 잔존 압축강도 특성을 검토하였다. 유기질 섬유의 혼입 방법으로 P.P, Nylon 섬유를 사용하였고, 내화 피복의 방법으로 포비성 Alkali-Silciates계 내화재를 사용하였다. 내화 시험은 자체 제작한 가열로에서 화염방사기를 이용하여 3시간 동안 화염 실험을 실시하였다. P.P 섬유를 혼입한 경우 폭렬은 방지 하였지만 잔존 압축강도는 측정할 수 없었고, 포비성 Alkali-Silicates계 내화재로 피복한 경우 폭렬 방지뿐만 아니라 잔존 압축강도가 최고 96%까지 유지되었다.

• 한국지반환경공학회 논문집
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• 제17권4호
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• pp.33-37
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• 2016

기존 뒤채움재의 대체방안으로 고려되는 유동성 채움재(Controlled Low Strength Material, CLSM)의 경화 특성 및 강도발현은 시공기간을 결정하는 주요 요소이다. 본 연구에서는 시간영역반사법(Time Domain Reflectometry, TDR)을 이용하여 유전상수를 도출함으로써 CSLM의 경화 특성을 모니터링하고, 산정된 유전상수와 일축압축강도간의 관계를 분석해보고자 하였다. CLSM 시료는 시멘트, 비회, 실트, 모래, 급결제 및 물로 배합되었으며 배합된 시료의 플로우, 단위중량, 일축압축강도와 같은 재료 특성을 조사하였다. 양생 기간 동안 CLSM의 유전율 특성을 모니터링하기 위하여 TDR 프로브가 설치된 몰드 및 Reflectometer를 이용하여 측정시스템을 구성하였다. 실험결과 유전상수는 양생 초기에 일정한 값을 유지하다, 시간이 진행됨에 따라 점차 감소하는 것으로 나타났다. 또한, 일축압축강도와 유전상수를 회귀분석한 결과 두 물성 사이에는 반비례적인 거듭제곱함수의 관계가 있음을 보여주었다. 본 연구에서 제안한 시간영역반사법을 이용한 CLSM의 특성 모니터링은 일축압축강도를 추정할 수 있는 현장 비파괴시험기법으로 효과적으로 사용될 수 있을 것으로 기대된다.

• Earthquakes and Structures
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• 제23권5호
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• pp.431-444
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• 2022

The unique thermomechanical properties of shape memory alloys (SMAs) make it a versatile material for strengthening and repairing structures. In particular, several research studies have already demonstrated the effectiveness of using the heat activated shape memory effect of nickel-titanium (Ni-Ti) based SMAs to actively confine concrete members. Despite the proven effectiveness and wide commercial availability of Ni-Ti SMAs, however, their high cost remains a major obstacle for applications in real structural engineering projects. In this study, the shape memory effect of a new, much more economical iron-based SMA (Fe-SMA) is characterized and the compressive behavior of concrete confined with Fe-SMA strips is investigated. Tests showed the Fe-SMA strips used in this study are capable of developing high levels of recovery stress and can be easily formed into hoops to provide effective active and passive confining pressure to concrete members. Compared to concrete cylinders confined with conventional carbon fiber-reinforced polymer (CFRP) composites, Fe-SMA confinement yielded significantly higher compressive deformation capacity and residual strength. Overall, the compressive behavior of Fe-SMA confined concrete was comparable to that of Ni-Ti SMA confined concrete. This study clearly shows the potential for Fe-SMA as a robust and cost-effective strengthening solution for concrete structures and opens possibilities for more practical applications.

• Composites Research
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• 제17권4호
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• pp.7-17
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• 2004

본 연구에서 복합재의 압축 강도에 대한 두께 효과가 $[0_4]_{ns},{\;}[45/0/-45/90]_{ns},{\;}[45_n/0_n/-45_n/90_n]_s$ (n=2 to 8) 등의 적층 방법을 이용하여 체계적인 실험을 통해 조사되었다. 여기서 섬유 체적비, 기공률, 섬유 굴곡도, 층간 응력 등, 적층 두께 증가에 따른 압축 강도에 영향을 주는 파라미터들이 실험과 이론적으로 연구되었다. 또한 엇교차 대칭 복합재판의 파괴강도에 대한 적층 순서 효과도 조사되었다. 이를 위해 2종류의 다른 스케일링 효과를 갖는 (1) 폰라이-레벨 기법인 $[45_n/0_n/-45_n/90_n]_s$과 (2) 서브라미네이트-레벨 기법인 $[45_n/0_n/-45_n/90_n]_s$가 적용되었다. 일 방향 적층 시편 $[0_4]_{ns}$과 플라이-레벨인 $[45_n/0_n/-45_n/90_n]_s$에는 분명한 두께효과를 나타내었다. 그리고 섬유 굴곡도와 기공률의 두께효과에 기여하는 주요 파라미터 들임이 확인되었다. 그러나 서브라미네이트-레벨인 $[45/0/-45/90]_{ns}$의 압축강도는 시편 두께의 변화에도 불구하고 별 영향을 나타내지 않았으면, 서브라미네이트- 레벨 시편에서 구한 강토가 플라이-레벨 시편에서 구한 강도보다 약간 높았다. 이 같은 효과에 대한 이유는 섬유 굴곡도, 기공률, 자유단 효과 및 $0^{\circ}$층과 비 $0^{\circ}$층 사이의 응력 재 분포에 의한 영향인 것으로 보인다. 측정된 파괴강도는 예측 값과 비교되었다.

• Geomechanics and Engineering
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• 제24권6호
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• pp.505-518
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• 2021

The present paper has been carried out to understand the effects of impact loading on the rock tunnels, constructed in different region corresponding to varying unconfined compressive strength (UCS), through finite element method. The UCS of rockmass has substantial role in the stability of rock tunnels under impact loading condition due to falling rocks or other objects. In the present study, Dolomite, Shale, Sandstone, Granite, Basalt, and Quartzite rocks have been taken into consideration for understanding of the effect of UCS that vary from 2.85 MPa to 207.03 MPa. The Mohr-Coulomb constitutive model has been considered in the present study for the nonlinear elastoplastic analysis for all the rocks surrounding the tunnel opening. The geometry and boundary conditions of the model remains constant throughout the analysis and missile has 100 kg of weight. The general hard contact has been assigned to incorporate the interaction between different parts of the model. The present study focuses on studying the deformations in the rock tunnel caused by impacting load due to missile for tunnels having different concrete grade, and steel grade. The broader range of rock strength depicts the strong relationship between the UCS of rock and the extent of damage produced under different impact loading conditions. The energy released during an impact loading simulation shows the variation of safety and serviceability of the rock tunnel.

• 소성∙가공
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• 제23권1호
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• pp.5-9
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• 2014

Although much research has been conducted to reduce the thickness of PET bottles in order to save manufacturing costs, the challenge remains of guaranteeing mechanical strength for top-loaded thin PET bottles. The current study investigates the large deformation characteristics of a circle shaped PET bottle and a square shaped PET bottle when compressively loaded using FEA. The arc length method is used in the nonlinear FEA to understand the buckling phenomenon. For PET bottles with the same capacity, the circle shaped bottle shows more resistance to buckling and compression loading than the square shaped bottle.