• Journal of Welding and Joining
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• 제24권3호
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• pp.42-48
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• 2006

Since the voids occur at the CD stud welds, the mechanism of void formation and void reduction method are investigated in this work. It is speculated that the voids are formed because of high short-circuit current above 1000A. When the simple flow model is used to estimate the void trapping condition, the most voids are trapped at the weld mainly due to fast cooling rate of the CD stud weld. Since it is almost impossible to remove the voids completely, a method is proposed to reduce the void by decreasing the short-circuit current at the end of the arcing time. The experimental results show that the void is reduced by decreasing the short-circuit current to 1000A.

• 한국정밀공학회지
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• 제18권12호
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• pp.159-166
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• 2001

Recently, high story apartments are common to solve a housing problem especially in major cities. Apartments are considered as clean, sanitary and convenient to live. However, There are some problems because residents share walls, floors and ceilings with other people. Thus, the residents are often disturbed by neighbours since sound travels the building elements. Especially, impact noise through the floors causes the many complains. And so, it has been drawn attention to isolate by the impact sound. The purpose of this study is to analyze the characteristics of vibration response of 12-type void slabs in the improved void slab by impedance method, and is to find the best improveds void slab on the 12-type void slabs.

• Nuclear Engineering and Technology
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• 제50권7호
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• pp.1190-1197
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• 2018

Analysis of the GRSW-A model coupled into the FALCON code is extended by simulation of central void formation in fuel pellets due to high-temperature fuel restructuring. The extended calculation is verified against published, well-known experimental data. Good agreement with the data for a central void diameter in pellets of the rod irradiated in an Experimental Breeder Reactor is shown. The new calculation methodology is employed in comparative analysis of modern BWR fuel behavior under assumed high-power operation. The initial fuel porosity is shown to have a major effect on the predicted central void diameter during the operation in question. Discernible effects of a central void on peak fuel temperature and Pellet-Cladding Mechanical Interaction (PCMI) during a simulated power ramp are shown. A mitigating effect on PCMI is largely attributed to the additional free volume in the pellets into which the fuel can creep due to internal compressive stresses during a power ramp.

• 한국실내디자인학회논문집
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• 제23권6호
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• pp.51-59
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• 2014

Rem Koolhaas has pursued new architectural approaches breaking with conventional ones. Around the 1990s when large-scale projects occurred with the union of Europe ahead, Koolhaas recognized the limits to the existing methods for responding to such changes. Accordingly, he came to use design methods based on 'congestion' and 'void' as strategical alternatives, which became the moment for him to leap forward from the previous working sphere based in Europe to becoming an architect who would be commissioned a number of large-scale global projects. Therefore, this study intends to investigate his design methods which utilized congestion and void, and to derive spatial characteristics from the projects based on such methods. First of all, the study looked into the historical background, definition and process of congestion and the void as design methods, and analyzed his projects to which such methods were applied by classifying them into the following categories: 1) the void that removes a space of singularity; 2) the void that penetrates space while making a flow; and 3) the void that is formed by vertical extrusion. Then, the characteristics of architectural spaces made in this way were identified as 1)the single-body appearance made by congestion and the following types of space made by the void: 2) the non-uniformly shaped space that looks like floating; 3) the flexible space with various flows and directions; and 4) the space with virtual possibilities that embrace contingent events. This understanding of Rem Koolhaas's design methods which were attempted in various ways at his critical turning point will be the foundation to understand the overall world of his works.

• 대한토목학회논문집
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• 제31권2A호
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• pp.121-127
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• 2011

콘크리트 내부에 존재하는 공극(void)의 공간적 분포는 콘크리트의 역학적, 물리적 거동에 큰 영향을 미친다. 따라서 콘크리트 재료 물성의 파악과 건정성 평가를 위해 내부에 존재하는 공극의 분포 상태를 파악하는 것은 매우 중요하다. 콘크리트에는 육안으로 보이는 재료 표면의 공극 이외에도 내부 공극이 존재한다. 본 연구에서는 경량골재 콘크리트의 공극 분포를 파악하기 위하여 micro CT(X-ray microtomography)를 활용하여 생성된 3차원 콘크리트 디지털 시편을 사용하였다. 흑백처리된 단면 이미지를 중첩하여 공극을 묘사할 수 있는 3차원 시편을 생성하였다. 공극의 분포 상태를 확률적으로 묘사하기 위하여 확률 분포 함수 two-point correlation function과 lineal-path function으로 분석하였다. 또한, 이미지 분석을 통해서 콘크리트 시편의 공극의 밀도 분포를 파악하였다. 콘크리트 내부에 있는 개별 경량 골재의 공극도 이미지 처리와 확률 분포함수를 사용하여 분석하였다. Micro CT와 3차원 이미지 분석 방법을 통하여 콘크리트 내부에 존재하는 공극의 분포 상태를 효과적으로 파악할 수 있음을 확인하였다.

• 자원리싸이클링
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• 제12권2호
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• pp.11-20
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• 2003

폐석회석을 투수 콘크리트용 골재로 활용하여 콘크리트의 공극률, 연속공극률, 투수계수, 압축강도 및 휨강도 등을 측정하였으며,투수 콘크리트의 공극특성과 강도와의 관계에 대하여 고찰하였다. 투수 콘크리트의 공극 및 강도특성은 폐석회석 혼합률에 의한 영향 보다는 골재입자의 크기 및 골재입자 사이의 공극에 의한 영향이 크게 작용하였다. 투수 콘크리트의 공극률과 연속공극률과의 관계 및 공극특성과 강도와의 관계도 양호한 선형관계를 나타내었다. 또한, 폐석회석을 사용한 투수 콘크리트의 투수계수는 0.2cm/sec 이상의 양호한 결과로 보통골재에 비하여 투수성능이 우수하였으며, 강도결과와 종합해 보면 폐석회석을 보도용 콘크리트 또는 식생, 수자원 정화 콘크리트 등으로 활용될 수 있을 것으로 기대되었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회 3차
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• pp.24-30
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• 2010

The void ratio and elastic moduli are design parameters used in geotechnical engineering to understand soil behavior. Elastic and electromagnetic waves have been used to evaluate the various soil characteristics due to high resolution. The objective of this study is to evaluate the void ratio and elastic moduli based on elastic wave velocities and electrical resistivity. The Field Velocity Resistivity Probe (FVRP) is developed to obtain the elastic and electromagnetic wave profiles of soil during penetration. The Piezoelectric Disk Elements (PDE) and Bender Elements (BE) are used as transducers for measuring the elastic wave velocities such as compressional and shear wave velocities. The Electrical Resistivity Probe (ERP) is also installed for capturing the electrical resistivity profile. The application test is carried out on the southern coast of the Korean peninsula. The field tests are performed at a depth of 6~20 m, at 10 cm intervals for measuring elastic wave velocities and at 0.5cm intervals for measuring electrical resistivity. The elastic moduli such as constraint and shear moduli are calculated by using measured elastic wave velocities. The void ratios are also evaluated based on the elastic wave velocities and the electrical resistivity. Furthermore, the converted void ratios by using FVRP are compared with the volumetric void ratio obtained by a standard consolidation test. The comparison shows that the void ratios based on the FVPR match the volume based void ratio well. This study suggests that the FVRP may be a useful device to effectively determine the elastic moduli and void ratio in the field.

• Computers and Concrete
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• 제20권2호
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• pp.165-176
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• 2017

Textile Reinforced Cementitious Composite (TRCC) became the most common construction material lately and have excellent properties. TRCC can be employed in the manufacture of thin-walled facade elements, load-bearing integrated formwork, tunnel linings or in the strengthening of existing structures. These composite materials are a combination of matrix and textile materials. There isn't much research done about the usage of polymer modified matrices in textile reinforced cementitious composites. In this study, matrix materials named as fine grained concretes ($d_{max}{\leq}1.0mm$) were investigated. Air entraining effect of polymer modifiers were analyzed and air void content of fine grained concretes were identified with different methods. Aim of this research is to study the effect of polymer modification on the air content of fine grained concretes and the role of defoamer in controlling it. Polymer modifiers caused excessive air entrainment in all mixtures and defoamer material successfully lowered down the air content in all mixtures. Latex polymer modified mixtures had higher air content than redispersible powder modified ones. Air void analysis test was performed on selected mixtures. Air void parameters were compared with the values taken from air content meter. Close results were obtained with tests and air void analysis test found to be useful and applicable to fine grained concretes. Air void content in polymer modified matrix material used in TRCC found significant because of affecting mechanical and permeability parameters directly.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2005년도 춘계 학술기술논문발표대회 논문집
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• pp.5-8
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• 2005

Sound absorbing performance is affected by porosity and continuity of void, therefore it is important to maintain stabilization of foam and to analyze properties of void pore in hardened state. The purpose of this study is to analyze the sound absorption properties and void characteristic of foamed concrete according to dilution ratio of foaming agent. The results of this experiment were as follows. It is determined that an increase in total and continuous void ratio is achieved by increasing of dilution ratio, and a shorter absorbing time was exhibited at a higher continuous void ratio. When the average void size of foamed concrete was below 1.5mm, the tendency of sound absorption coefficient compared with general sound absorber was appeared similarly.

• 한국지반환경공학회 논문집
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• 제14권3호
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• pp.13-17
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• 2013

Determination of geotechnical characteristics of soil is either to use the field samples to measure the characteristics of soil through laboratory test or measuring the characteristics directly in the field. Field test can be derived similar value by considering characteristics of site and laboratory test can be confirmed the characteristic of soil by testing with field samples. This article describes relative density as the measure of compaction for cohesionless soils and presents several simple and mathematical relationships to help engineers estimate needed parameters for relative density calculations. The main purpose of this research is to investigate possible correlations between coefficient of uniformity, coefficient of curvature, maximum and minimum void ratio, mean grain size. Results show a linear relationship between the minimum and maximum void ratios and a power function relationship between coefficient of uniformity and the limiting void ratios. Void ratio range, which is the difference between the maximum and minimum void ratios, appeared to be log normally distributed but showed no simple mathematical fit to the data. these results were shown to help engineers estimate needed parameters for relative density calculations.