• 한국구조물진단유지관리공학회 논문집
• /
• 제19권6호
• /
• pp.63-71
• /
• 2015

본 연구는 섬유를 혼입한 고강도 콘크리트의 온도 변화에 따른 내화특성 분석에 관한 연구로 고강도 콘크리트에 고온이 가해질 경우 발생되는 폭렬현상에 대하여 방지효과가 있는 것으로 알려져 있는 하이브리드섬유와 강섬유를 함께 혼입하여 만든 복합섬유를 사용하여 온도 변화($100{\sim}800^{\circ}C$)에 따른 고강도 콘크리트의 내화특성 및 역학적 메커니즘을 분석하였다. 또한 본 논문에서는 고강도 콘크리트 구조물에서 가장 문제가 되는 폭렬현상을 막는 대책 중의 하나인 섬유 혼입을 통한 방법을 사용하여 SEM 및 XRD 분석 등의 방법으로 고온을 받은 고강도 콘크리트의 열적 특성 및 역학적 특성을 규명하고자 하였다.

• Structural Engineering and Mechanics
• /
• 제84권5호
• /
• pp.575-590
• /
• 2022

In this paper, bond-slip behavior of high strength concrete filled circular steel tube (HSCFCST) after elevated temperatures treatment was studied. 17 specimens were designed for push-out test. The influence was discussed as following parameters: (a) concrete strength, (b) constant temperature, and (c) bond length. The results showed that (1) after elevated temperatures treatment, the bond strength of the HSCFCST specimens increased first and then decreased with temperature rising; (2) the bond strength increased with the increase of concrete strength at room temperature, while the influence subsided after elevated temperatures treatment; (3) the strain of the circular steel tube was distributed exponentially along its length, the stress changed from exponential distribution to uniform distribution with the increase of load; (4) the bond damage process was postponed with the increase of constant temperature; and (5) the energy consumption capacity of the bonding interface increased with the rise of concrete strength and constant temperature. Moreover, computational formulas of ultimate and residual bond strength were obtained by regression, and the bond-slip constitutive models of HSCFCSTs after elevated temperatures was established.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2006년도 춘계학술논문 발표대회 제6권1호
• /
• pp.5-8
• /
• 2006

High strength concrete has been increasingly used in high rue building and it is very obvious re consider fire resistance performance of that. Unlike the normal strength concrete, high strength concrete in sudden elevating temperature at fire is susceptible to spalling with severe explosion and surface split, due to high density of concrete. In order to endure the spalling, inner space temperature of concrete should be control less than certain point. Therefore this study investigated the influence of covering materials on high strength concrete finishing spray-on materials of fiber composite spray mortar(FCSM). Both polypropylene(PP) and polyvinyl alcohol(PVA) fiber were used in this test. Test showed that concrete, covering 18mm mortar containing PVA fiber and confining metal lath 2.3mm thickness, decreased 50% of main bar ambient temperature. compared with control concrete. In addition, concrete covering 18mm mortar without fiber caused falling of covering materials and then it was exposed in elevating temperature. As a result, spatting of the concrete occurred same as control concrete. However, concrete covering spray-on mortar containing PVA or PP fiber resisted spatting occurrence.

• 콘크리트학회논문집
• /
• 제25권6호
• /
• pp.613-620
• /
• 2013

콘크리트는 고온에 강한재료로 인식되어 왔으나, 화재 등의 고온에 의해 내부조직의 물리 화학적 변화가 발생해 역학적 특성이 저하하게 된다. 이에, 고온시 콘크리트의 역학적 특성의 저하에 관한 연구보고 및 기준이 제시되고 있다. 그러나 고강도 콘크리트 및 하중을 재하한 상태에 관한 연구데이터는 적다. 따라서 이 연구에서는 고온 및 하중재하에 따른 고강도 콘크리트의 고온특성을 평가하였다. W/B 12.5%, 14.5%, 20%의 고강도 콘크리트를 대상으로 비재하상태 및 $0.25f_{cu}$의 하중조건을 설정하여, 고온시의 응력-변형, 최대하중에서의 변형, 압축강도, 탄성계수, 열팽창변형, 단기 고온크리프을 평가하였다. 실험 결과, 압축강도가 높아질수록 가열에 의한 압축강도의 저하가 크게 나타났고, $500^{\circ}C$이상의 온도에서 고온에 의한 열팽창변형과 하중재하에 의한 수축변형이 상쇄되어 압축강도 및 탄성계수의 잔존율이 높아지는 것을 확인할 수 있었다.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
• /
• pp.339-344
• /
• 2001

This study is to investigate properties of high strength.high flowing concrete using blast-furnace slag in temperature conditions of 5, 10, 15 and $20^{\circ}C$. The result of this study can be summarized as follows. 1) The use of blast-furnace slag leads to decrease of air content and increase of fluidity in the fresh concrete. 2) The early compressive strength of high strength.high flowing concrete containing blast-furnace slag is lower than the case with portland cement only. 3) The compressive strength development of incorporating in the concrete is poor at low temperature below about $15^{\circ}C$.

• 한국재료학회지
• /
• 제24권10호
• /
• pp.520-525
• /
• 2014

Effects of Cu and B on effective grain size and low-temperature toughness of thermo-mechanically processed high-strength bainitic steels were investigated in this study. The microstructure of the steel specimens was analyzed using optical, scanning, and transmission electron microscopy; their effective grain size was also characterized by electron back-scattered diffraction. To evaluate the strength and low-temperature toughness, tensile and Charpy impact tests were carried out. The specimens were composed of various low-temperature transformation products such as granular bainite (GB), degenerated upper bainite (DUB), lower bainite (LB), and lath marteniste (LM), dependent on the addition of Cu and B. The addition of Cu slightly increased the yield and tensile strength, but substantially deteriorated the low-temperature toughness because of the higher volume fraction of DUB with a large effective grain size. The specimen containing both Cu and B had the highest strength, but showed worse low-temperature toughness of higher ductile-brittle transition temperature (DBTT) and lower absorbed energy because it mostly consisted of LB and LM. In the B-added specimen, on the other hand, it was possible to obtain the best combination of high strength and good low-temperature toughness by decreasing the overall effective grain size via the appropriate formation of different low-temperature transformation products containing GB, DUB, and LB/LM.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2012년도 추계 학술논문 발표대회
• /
• pp.263-264
• /
• 2012

In this study, the ultra high strength concrete which have 100, 150, 200MPa took the heat from 20℃ to 70 0℃ and the 0, 20% stress in normal condition's to evaluate stress-strain, residual compressive strength and thermal expansion deformation were evaluated. The heating speed of specimen was 0.77℃/min 20~50℃, 50℃ before the target temperature, and the other interval's heating speed was 1℃/min. As a result, the stress-strain curve of non-load specimen showed the liner behavior at high temperature when the specimen's strength increased more. If ultra high strength concrete got loads, its compressive strength tended to decrease different from the normal strength concrete. The thermal expansion deformation was expanded from a vitrification of quartz over 500℃. however, over the 600℃, it was shrinked because of the dehydration of the combined water.

• Tribology and Lubricants
• /
• 제35권1호
• /
• pp.24-29
• /
• 2019

In this work we investigated the friction and wear characteristics of a magnesium alloy, which has been receiving much attention as a light metal in industrial applications such as automobiles and aerospace. Magnesium is one of the lightest structural material that has high specific strength, lightweight, low density and good formability. However, current issue of using magnesium alloy is that magnesium has weakness against temperature. As the temperature increases, magnesium undergoes poor creep resistance and ease of softening, and therefore, its mechanical strength decreases sharply. To solve this issue, a new type of magnesium alloy that retains high strength at high temperature has been proposed. The tribological behavior of this alloy was investigated using a tribotester with reciprocating motion and heating plate. A stainless steel ball was used as a counter surface. Results showed that extrusion process has similar wear behavior to the commonly used casting process but retains good mechanical strength and durability. The presence of an alloying element enhanced the wear properties especially in high temperature. This study is expected to be utilized as fundamental data for the replacement of high density materials currently used in mechanical industries to a much lighter and durable heat-resistant materials.

• 대한기계학회논문집A
• /
• 제33권11호
• /
• pp.1233-1238
• /
• 2009

This study analyzed the characterization of high temperature strength of $Si_3N_4$ composite ceramics additive based on variations in the amount of nano colloidal $SiO_2$ added. Semi-elliptical cracks about 100 ${\mu}m$ length were obtained from a Vickers indenter using a load of 24.5 N. The results showed that the heat-treated smooth specimens with $SiO_2$ nano colloidal coating exhibited the highest bending strength at 0.0 wt% $SiO_2$ nano colloidal added, which is amounted to a 187 % increase over that of smooth specimen. Limiting temperature for bending strength of crack-healed zone for bending strength was about 1273 K. However, the bending strength of SSTS-3 and SSTS-4 was considerably increased while that of SSTS-1 and SSTS-2 was decreased at a temperature of 1,573K.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2005년도 춘계 학술기술논문발표대회 논문집
• /
• pp.37-40
• /
• 2005

High Performance Concrete(HPC) has been widely used in high-rise building. The HPC has several benefits including high strength, high fluidity and high durability. However. spatting is susceptible to occur in HPC and HPC also tends to be deteriorated in the side of fire resistance performance at fire. This paper focuses on the analysis of the temperature history and residual compressive strength with finishing material, in order to protect HPC from sudden-high-temperature, which is one of the main reason spatting occurs. Test results show that spalling occurs in all specimens. The most serious spalling took placed in HPC covering fire enduring spray-on material, whose covering thickness is 20mm but temperature history indicates that fire enduring spray effectively protected HPC from fire for more than 2hours. In addition, residual compressive strength ratio of HPC using fire enduring paint was more than $90\%$ of original strength, thus minimizing spatting and indicating significant fire resistance performance.