• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.696-696
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• 2012

호안은 유수의 침입으로부터 제방 및 하안의 침식 피해를 방지하기 위해 제방에 설치되는 구조물이다. 침식에 의한 제방 및 호안의 대표적인 붕괴특성 중에는 만곡부, 하천 급경사, 지형의 간섭효과 등이 있다. 특히, 만곡부는 원심력, 2차류 등에 의한 수위상승 및 유속증가로 제체에 응력 집중이 발생되어 안정성 저하를 유발할 수 있다. 또한, 만곡부의 흐름 방향전환 현상은 하도내 통수능 저하를 발생시켜 홍수피해를 가중시킬 수 있다. 따라서 하천특성상 만곡부에 의해 발생할 수 있는 홍수피해 요소를 저감시킬 수 있도록 적합한 피해저감대책을 마련할 필요가 있다. 제방의 보강대책으로서 활용되고 있는 호안은 역학적인 측면에서 외력과 저항력의 크기에 따라 안정성이 평가되어야 하며 지역여건 등에 따른 만곡부의 수위상승 및 제방 침식 등을 고려한 설계가 수행되어야 한다. 국내 실무에서 적용되고 있는 호안설계방법은 하천설계기준 해설(2009)을 참고하고 있는데, 흐름현상 및 만곡부 특성 등에 대하여 경험과 이론의 양면을 고려한 설계를 수행하도록 제안하고 있다. 이는 호안 안정성에 대한 역학적 검토 방법의 한계로 비합리적 설계가 될 우려가 있다. 따라서 만곡부에 의한 유속 및 소류력 등 흐름특성을 고려한 정량적인 평가기법이 요구되는 상황이다. 본 연구에서는 수리실험을 통해 만곡에 의한 흐름영향과 수리학적 거동 및 설계요소를 파악하고자 만곡부에 사석호안공을 설치하여 흐름전환 및 유속변화에 따른 사석호안공의 이탈현상을 재현하였다. 실험수로는 곡률반경( )이 4.5 m인 만곡부가 3개소 발생하는 폭 2.3 m, 길이 25 m의 다중 사행수로 형태이다. 실험수로 우안의 1V:2H 경사면에 10, 20, 30, 40, 50 mm 사석을 크기별로 설치하여 만곡에 의한 유속변화 등 흐름현상과 호안공 이탈을 관찰하였다. 수리실험은 고정상으로 수행되었으며 정상류 흐름조건에서 공급유량별 하류단 수위 조절을 통해 만곡부내 호안 공 이탈을 발생시키는 설계인자를 도출하고자 유속과 수심을 측정하였다. 실험결과를 바탕으로 사석호안공 설계시 1차원 접근유속에 만곡 영향을 고려하여 대표유속으로 적용하는 방법의 특성을 파악하고, 사석호안공의 이탈유속과 만곡에 의한 흐름특성간의 상관관계를 분석하여 제원결정기법을 제안하였다.

• Journal of Korean Society of Steel Construction
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• v.14 no.1
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• pp.87-94
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• 2002

In the preceding study, a series of results was presented according to factors like as attaching method of main bar, shear span to depth ratio, reinforcing method for different types of region among various factors, which could determine the properties of composite beams. Based on these results, this study was planned to investigate the structural behaviors of according to attaching method of main bar for composite beams(end-reinforced concrete(RC), center-steel concrete (SC)) varying ratio of tensile bar to steel mainly. Consequently, there were little difference according to attaching method of main bar. And as the ratio of tensile bar to steel increase, the efficiency of strength was high, but ductile capacity of beams could deteriorate. Therefore, to maximize the structural properties of composite beams, it was considered that the ratio of tensile bar to steel should be limited.

• Fire Science and Engineering
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• v.21 no.2 s.66
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• pp.54-63
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• 2007

Concrete is generally accepted to have good inherent fire resistance. It mainly relies on the assumption that concrete has low heat-transfer characteristic and spatting does not occur during the course of a fire. However, the significant numbers of fire accidents have shown in recent years that incidence of spatting has caused sever damages to many structures. This review has systematically investigated the behaviour of concrete in fire, including phenomenon of spatting, with respect to the theorical consideration and experimental results. Explosive spatting is caused by the build-up of water vapor pressure in concrete subjected to increasing temperatures. When this pressure exceeds the tensile strength of the concrete over a fire-exposed area, explosive spatting can result in a typical temperature range between $200^{\circ}C\;and\;400^{\circ}C$. The major functions are known to be moisture content, pore pressure, load ratio, and heating regime.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.5
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• pp.513-520
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• 2011

In this paper, the advanced explicit algorithm is proposed to simulate the stress-erection process analysis of Strarch system. The Strarch(Stressed-Arch) system is a unique and innovative structural system and member prestress comprising prefabricated plane truss frames which are erected by a post-tensioning stress-erection procedure. The flexible bottom chord which have sleeve and gap detail are closed by the reaction force of prestressing tendon. The prestress imposing to the tendon will make the Strarch system to be erected. This post tensioning process is called as "stress-erection process". During the stress-erection process, the plastic rigid body rotation is occurred to the flexible top chord by the excessive amount of plastic strain, and the structural characteristic becomes to be unstable. In this study, the large deformational beam-column element with plastic hinge is used to model the flexible top chord, and the advanced Dynamic Relaxation method(DRM) are applied to the unstable problem of stress-erection process of Strarch system. Finally, the verification of proposed explicit algorithm is evaluated by analysing the stress-erection of real project of Strarch system.

• Korean Journal of Materials Research
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• v.11 no.4
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• pp.278-282
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• 2001

The recombination motion of Partial dislocations on basal slip (0001) 1/3<1120> in sapphire ($\alpha$-Al$_2$$O_3$) single crystals was investigated using the four-point bending test with the prism plane (1120) samples. These bending experiments were carried but in the temperature range from $1200^{\circ}C$ to $1400^{\circ}C$ at various engineering stresses 90MPa, 120MPa, and 150MPa. During these tests it was shown that an incubation time was needed for basal slip to be activated. The activation energy for the incubation time was 5.6-6.0eV in the temperature range from $1200^{\circ}C$ to $1400^{\circ}C$. The incubation time is believed to be related to recombination of climb dissociated partial dislocations via self-climb. In addition, these activation energies are nearly same as those for oxygen self-diffusion in $Al_2$$O_3$ (approximately 6.3 eV). Thus, the recombination of the two partial dislocations would be possibly controlled by oxygen diffusion on the stacking fault between the partials.

• Journal of the Korea Concrete Institute
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• v.29 no.1
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• pp.77-84
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• 2017

In this study, the structural performance of high strength concrete (HSC) column-normal strength concrete (NSC) slab connection was investigated according to confinement effects, aspect ratio (h/c) and strength ratio ($f^{\prime}_{cc}/f_{cs}$). The study was conducted by using finite element analysis. To verify the analysis methods, the experiments and analyses results were compared. The specimens were classified by connection types including interior column, edge column, corner column and isolated column. As a result, ultimate strength of interior column was larger than other specimens. Also, the axial stresses of connection were decreased when the aspect ratio was increased. As the strength ratio between column and slab was increased, the ultimate strength of specimens was also increased until the strength ratio was reached to 1.83.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.6
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• pp.175-182
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• 2006

In the design of composite structures, shear connectors such as headed stud, channel, perforated plate, etc, are commonly used to transfer longitudinal shear forces across the steel-concrete interface. Many researches have been conducted to improve the characteristics of different types of shear connector. This paper presents the results of 11 push-out tests performed on the new perforated rib connectors with shearing bars embedded in concrete slab under static loads. The results obtained from these tests are as following : 1) The bearing plate welded on both sides of perforated rib plate improves the stiffness and strength. 2) The capacity of perforated connectors is influenced primarily by the transverse reinforcements and shearing bars.

• Nuclear Engineering and Technology
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• v.19 no.1
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• pp.22-33
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• 1987

The confirmed integrity of nuclear fuel cladding materials is an important object during steady state and transient operations at nuclear power plant. In this context, the clad material yielding behavior is especially important because of pellet-clad gap expansion. During the steep power excursion, the in-pile irradiation behavior differences between uranium-dioxide fuel pellet and zircaloy clad induce the contact pressure between them. If this pressure reaches the zircaloy clad yield pressure, the zircaloy clad will be plastically deformed. After the reactor power resumed to normal state, this plastic permanent expansion of clad tube give rise to the pellet-clad gap expansion. In this paper, the simple mandrel expansion test method which utilizes thermal expansion difference between copper mandrel and zircaloy tube was adopted to simulate this phenomenon. That is, copper mandrel which has approximately three times of thermal expansion coefficient of zircaloy-4 (PWR fuel cladding material) were used in this experiment at the temperature range from 400C to 700C. The measured plastic expansion of zircaloy outer radius and derived mathematical relations give the yield pressure, yield stress of zircaloy-4 clad at the various clad wall temperatures, the activation energy of zircaloy tube yielding, and pellet-clad gap expansion. The obtained results are in good agreement with previous experimental results. The mathematical analysis and simple test method prove to be a reliable and simple technique to assess the yielding behavior and gap expansion measurement between zircaloy-4 tube and uranium-dioxide fuel pellet under biaxial stress conditions.

• Journal of Korean Society of Steel Construction
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• v.25 no.2
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• pp.131-139
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• 2013

The object of this paper is to perform the experiments to investigate the relationship of the resistance forces and the failure temperatures on the failure behaviors of H-shaped steel compressive members. H-shaped members(SS400) were used for the test models and the tests for the elevated temperatures were performed by ISO 834 in FILK(Fire Insurers Laboratories of Korea). The local, overall buckling stresses and a yielding stresses for the failure temperatures were compared with the compressive stresses for the loading forces of test models, the yielding strength and elastic modulus reduction factor of the steel at a high temperature were based on the criteria of the EC3(Eurocode 3) Part1.2(1993). The slenderness ratio was fixed by 45.4 and the compressive forces corresponded with 50%, 70% and 80% of the yielding forces at the normal temperatures were chosen for the loading forces of the test models. The failure temperatures of the test models were investigated under three kinds of loading conditions. It was known that the resistance forces have come close to the yielding forces, not the elastic buckling loads evaluated by EC3 at the failure temperatures obtained from the tests which are related to the failure temperatures and the loading stresses.

• Journal of the Korean Geotechnical Society
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• v.26 no.2
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• pp.23-32
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• 2010

This study was especially conducted to find out the characteristics of the lightweight air-mixed soil (slurry density 10 kN/$m^3$) containing silt related to water. Compression strength, permeability, and capillary height of the lightweight air-mixed soil were studied, and also to support these studies, the structure of that soil was analyzed in detail. Air bubbles of various sizes are inside the lightweight air-mixed soil, and its distribution in a location is almost constant. A numerous tiny pores are inside the air bubbles so that the lightweight air-mixed soil can be saturated with water. Porosity is also estimated through the image analysis. Peak strength of the lightweight air-mixed soil is not dependent on water, but behavior of stress-strain is affected by the water. Permeability is about $4.857{\times}10^{-6}cm/sec$, which is a little bit higher than the clay's permeability. Capillary rise occurs rapidly at the beginning of the test until the lapse of 100 minutes and then its increase rate becomes slow. The capillary rise causes the increase of the density of the lightweight air-mixed soil, and thus it is required to pay attention to this phenomenon during structure design and maintenance of the lightweight air-mixed soil.