• Journal of Korean Society of Steel Construction
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• v.22 no.6
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• pp.523-532
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• 2010

Concrete-filled square steel tube (CFT) columns have inherently high fire resistance and load-bearing capacity. Nevertheless, it is sometimes necessary to improve their fire resistance using external fire protection. This paper presents the experimental results of the temperature distribution of CFT columns with fire protection. A fire load test was carried out by exposing small-scale specimens to heat in an electric furnace that was especially built for testing loaded columns. The temperature distribution of CFT columns under constant axial loads was determined, as were its significant parameters, such as the types of fire protection and thickness, the thickness of the square CFT, and the fire duration times. The results of this study showed the temperature distribution of each specimen of the electric furnace and the temperature distribution properties of concrete and steel. In addition, the axial displacement and local buckling behavior of CFT columns based on temperature changes was observed.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.753-761
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• 2009

This paper presents the test results of total 24 beam-end specimens to investigate the effect of high-strength concrete and cover thickness on the development resistance capacity in tensile lap splice length regions. Based on bond characteristics that an increase in concrete strength results in higher bond stress and shortening of the transfer length, cracking behavior that thin cover thickness induced a splitting crack easily and brittle crack propagation, current design code that development length provisions as uniform bond stress assumption was investigated apply as it. The results showed that as higher strength concrete was employed, not only development resistance capacity was influenced by cover thickness, but also more sufficient safety factor reserved shorter than the lap splice length provision in current design code. From experimental research results, high-strength concrete development length was not inverse ratio of $\sqrt{f_{ck}}$ but directly inverse of $f_{ck}$, and it is also said that there is a certain limit length of the embedded steel over which the assumption of uniform bond stress distribution is valid specially for high-strength concrete not having a same embed length such as normal-strength concrete in current design criteria hypothesis.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.4
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• pp.78-85
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• 2010

When the fire occur, concrete filled steel tube(CFT) columns expected to form a much distinction in a fire resistance performance according to a kind of fire protection because the steel surface is directly exposed to high temperature. In this study, an experiment by three factors which were kind of fire protection, thickness of protection and time was performed to get the characteristics of temperature distribution types of CFT column with fire protection. As the result of this study, on a basis of heating temperature, spray protection was the most superior in a fire resistance performance, fireproof paint was next, and without fire protection was most inferior. In a heating time-location relationship, the temperature increased slowly on the surface of the concrete, but the temperature increased sharply on the surface of the steel.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.1
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• pp.79-88
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• 2023

In this study, a development of the rust formation arising from steel corrosion was modelled to quantify the structural impact in steel reinforced concrete. The interfacial gap, cover depth and diameter of steel rebar were taken for variables in modelling. It was found that the interfacial gap was the most influencing on the structural limit at steel corrosion, followed by steel diameter and cover depth. At 75 mm of cover depth with 20 mm of the steel diameter, the rust amount to reach cracking accounted for 16.95-27.69 ㎛ to 1-10 ㎛ of the interfacial gap. It was found that there was no risk of cracking and structural limit until the rust was formed within the interfacial gap. With a further formation of rust, the concrete section was successively behaved to yielding, cracking and failure. Additionally, the interfacial gap was the most dominant parameter for the rust amount to reach the cracking of concrete at the interfacial zone, whilst the cover depth had a marginal effect on cracking but had a crucial influence on the rust to failure.

• Magazine of the Korea Concrete Institute
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• v.14 no.2
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• pp.37-44
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• 2002

콘크리트의 내화성능에 대한 다각적인 연구가 1970년대부터 원자로의 안정성 확보차원에서 진행되어 왔으며 특히 콘크리트의 취성파괴(brittle failure)등에 대한 연구가 많다. 콘크리트의 내화성이란 화재로부터 보호되고 고열환경에 견디는 재료적 특성 즉 화재온도 1,00$0^{\circ}C$ 정도의 고온을 30분에서 3시간 정도를 받은 경우 콘크리트 중에 매립된 철근 등 철강을 소정의 온도 이하고 유지하기 위한 피복 역할을 유지하면서 구조물의 큰 변형이나 붕괴 등을 막기 위한 소요 압축강도 및 영계수 등의 성능을 가지고 있는 성질을 말한다.(중략)

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3A
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• pp.265-275
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• 2010

Concrete filled steel tube and concrete encased steel tube columns are expected to have confined effects of concrete by steel and reinforced effects of local buckling by concrete. On the basis of confined state concrete models of previous researches, stress-strain and load-displacement relations of RC, CFT and CET columns are analyzed by steel ratio. After comparing analysis results with experimental results, Modified stress-strain relations are derived through evaluation the influence upon confined effects of concrete in each cases. Also, the modified stress-strain models are carried out to be compared with specified strength of various countries.

• Journal of the Korea Concrete Institute
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• v.25 no.6
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• pp.621-630
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• 2013

Several techniques for steel corrosion detection are proposed and HCP (half cell potential) technique is widely adopted for field investigation. If concrete has cracks on surface, steel corrosion is rapidly accelerated due to additional intrusion of chloride and carbon dioxide ions. This study is for an evaluation of HCP in cracked concrete exposed chloride attack. For this work, RC (reinforced concrete) beams are prepared considering 3 w/c ratios (0.35, 0.55, and 0.70) and several cover depths (10~60 mm) and various crack widths of 0.0~1.0 mm are induced. For 35 days, SST (salt spraying test) is performed for corrosion acceleration, and HCP and corrosion length of rebar are evaluated. With increasing crack width, w/c ratios, and decreasing cover depth, HCP measurements increase. HCP evaluation technique is proposed considering the effects of w/c ratios, crack width, and cover depth. Furthermore anti-corrosive cover depths are obtained through Life365 program and the results are compared with those from this study. The results shows relatively big difference in cracked concrete, however provide similar anti-corrosive conditions in sound concrete.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.266-266
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• 2012

오늘날 도시는 인간 중심적으로 환경을 고려하지 않은 채 개발위주의 발전이 계속되고 있으며 도시화가 진행됨에 따라 도심지에 콘크리트와 아스팔트의 비율이 증가하고 농경지와 녹지가 감소하는 등 도시주변의 피복 변화가 빠르게 일어나고 있다. 이와 같이 열 환경을 고려하지 않은 도시의 급성장은 각종 인공 열과 대기오염 물질의 증가와 함께 도시상공의 기온을 상승시켜 도시의 기온이 주변 지역보다 높아지는 열섬현상의 원인이 되고 있다. 이에 따라 최근 미국, 유럽 등의 선진국을 비롯하여 아시아지역에서도 도시열섬현상 대책수립이 활발히 진행되어오고 있으며 국내에서도 열섬완화 대책 수립의 중요성이 인식되고 있다. 그러나 자연토지피복은 농경지, 나지, 수면과 같은 다양한 종류의 피복으로 구성되며 각 피복특성에 따라 도시내부에 영향을 미치는 정도가 다르게 나타나므로 도시계획에 반영될 수 있는 자연피복의 종류와 피복비율의 적정조합을 도출할 필요가 있다. 따라서 본 연구에서는 청주시를 대상으로 농경지를 포함하는 녹지의 감소, 공업단지의 증가에 따른 열 환경 영향을 분석하기 위하여 청주시의 연도별 토지피복 분포 현황과 과거 기상자료를 통해 토지피복 분포변화에 따른 온도 변화를 조사하였다. 토지피복은 농경지, 녹지, 주거지, 공업 단지 및 수역으로 분류하였으며, 대상지역의 기후 특성 파악을 위하여 청주시 총 면적에 대한 면적비율의 증감추이와 그에 따른 온도 변화를 정량적으로 파악하였다. 그 결과, 청주시는 녹지의 경우 정체 또는 감소추세를 나타낸 반면 공업단지는 지속적인 증가추세를 나타내었다.

• Journal of the Korea Concrete Institute
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• v.24 no.6
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• pp.761-768
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• 2012

The purpose of this study is to investigate bond properties of GFRP used in SFRC (Steel fiber reinforced concrete) and normal concrete. The experimental variables were rebar diameter (D13, D16), steel fiber volume fraction (0~2%) and cover thickness ($1.5d_b$, $5.4d_b$). The experimental results showed a different failure mode depending on the cover thickness. Through the tested specimens, splitting failure occurred for the specimens with small cover thickness and pull out failure occurred in the specimens with large cover thickness. Introduction of steel fiber caused the specimens to have more ductile behavior of bond stresss-lip after peak stress, but they did not increase the bond strength significantly. These failure modes were shown in both steel reinforcement and GFRP. However, from the difference of micro structure of bond failure mechanism between steel rebar and GFRP rebar, more ductile behavior was observed in GFRP-specimens after maximum bond strength was reached.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2011.11a
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• pp.115-118
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• 2011

본 연구에서는 현재 법정내화구조로 규정되어 있는 철근콘크리트(RC: Reinforced concrete)조 및 철골철망모르타르(SWM: Steel & Wire Mortar)조 슬래브에 대하여 재하조건에서 구조별 내화성능을 검토하고, 철골철망모르타르조 슬래브에 대해서는 피복두께별 내화성능을 검토하고자 표준화재조건에서 내화실험을 실시하였다. 실험결과 동일피복 두께일 경우 철근콘크리트조 슬래브가 내화성능이 우수한 것으로 나타났으며, 철골철망 모르타르조 슬래브의 경우 피복두께가 10mm 증가 시 7%의 내화성능이 향상되는 것으로 나타났다. 가열 이면온도는 슬래브의 두께가 늘어날수록 낮은 것으로 나타났다.