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혼화재 종류에 따른 PSC 교량용 그라우트의 재료특성 평가
원천봉(Yuan Tianfeng),류두열(Yoo Doo-Yeol),고경택(Koh Kyung-Taek ),윤영수(Yoon Young-Soo) 한국방재학회 2018 한국방재학회논문집 Vol.18 No.2
본 연구에서는 플라이 애시(FA), 보통 실리카퓸(SF)과 지르코늄 실라카퓸(Zr)을 사용한 PSC 그라우트의 재료특성을 평가하였다. 실험결과, FA와 Zr을 사용한 그라우트 배합들은 적은 감수제 혼입량에서도 우수한 유동성을 나타냈으나, 계획된 시간에 측정된 블리딩 및 체적변화량은 증가하였다. 압축강도는 모든 그라우트 배합들에서 재령 7, 28일에 우수한 강도 발현을 나타났고, 3성분계 그라우트 배합들은 2성분계 그라우트보다 우수한 거동을 보였다. 또한 3성분계 그라우트 배합들을 수축저감제(SRA)와 팽창재(EA)를 병용하여 자기수축 특성을 평가한 결과, SRA와 EA를 사용함으로써 자기수축을 47~80% 저감하였으며, SF을 사용한 그라우트 배합에서 효과적인 수축저감 특성을 나타냈다. This experimental study investigates material properties of prestressed concrete (PSC) grout depend on the combination of fly ash (FA), silica fume (SF) and zirconia silica fume (Zr). Based on the test results, when FA and Zr were included in grout mixtures, the fluidity, bleeding and volume change increased with less superplasticizer. The compressive strength of all grout mixtures was quite high at the age of 7 and 28 days, and the ternary mixtures had the excellent development of strength than binary mixtures. Furthermore, autogenous shrinkage properties of ternary grout combining shrinkage reducing agent (SRA) and expansive additive (EA) was evaluated. The 47~80% autogenous shrinkage was reduced by using SRA and EA. In addition, the effectiveness of using SRA and EA was higher for the grout mixture with SF than that with Zr.
Yoo, Doo-Yeol,Yuan, Tianfeng,Yang, Jun-Mo,Yoon, Young-Soo Elsevier 2017 ENGINEERING STRUCTURES Vol.147 No.-
<P><B>Abstract</B></P> <P>This study aims to investigate the feasibility of eliminating the minimum shear reinforcement in reinforced sustainable high-strength concrete (HSC) beams by incorporating 0.75% (by volume) of hooked steel fibers. To do this, five large reinforced HSC beams, with and without stirrups and steel fibers, were fabricated and tested. In order to have minimum shear reinforcement, the reinforced HSC beams were designed with longitudinal steel bar ratios of 0.64–0.72%. Test results indicate that the use of 0.75vol% of steel fibers (instead of stirrups) leads to higher flexural strength but lower ultimate deflection and ductility. The failure mode of lightly-reinforced HSC beams was transformed from concrete crushing to longitudinal steel bar rupture by including the steel fibers. However, both the reinforced HSC and steel-fiber-reinforced concrete (SFRC) beams exhibited flexural failure modes; as a result, it was concluded that the minimum shear reinforcement for reinforced HSC beams can be efficiently eliminated by including 0.75vol% of hooked steel fibers. In addition, the flexural behavior of reinforced SFRC beams was successfully simulated based on sectional analysis by considering fiber orientation factor.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Minimum shear reinforcement in HSC beam can be eliminated by adding 0.75% hooked steel fibers. </LI> <LI> Adding steel fibers increases flexural strength but decreases ductility of HSC beams. </LI> <LI> Reinforced SFRC beam without stirrup is failed by premature rupture of steel rebar. </LI> <LI> The use of ultimate ductility index is appropriate for reinforced SFRC beam. </LI> <LI> An appropriate equation of fiber orientation factor for high-strength SFRC is proposed. </LI> </UL> </P>
철근 배근 방법에 의한 철근콘크리트의 전자파 차폐특성 평가
최진석(Choi, JinSeok),원천봉(Yuan, TianFeng),홍세희(Hong, SeHee),윤영수(Yoon, YoungSoo) 한국방재학회 2020 한국방재학회논문집 Vol.20 No.5
본 연구에서는 콘크리트의 두께와 철근 보강에 따른 철근콘크리트의 전자파 차폐특성에 관한 실험을 수행하였다. 또한, 섬유보강 콘크리트의 강섬유 혼입률 및 철근 간격에 따른 전자파 차폐특성을 평가하였다. 콘크리트는 두께의 증가에 따라 높은 주파수 대역에서 전자파 차폐에 큰 효과를 나타냈으며 철근은 직경의 증가, 철근 간격의 감소 및 보강 층의 증가에 따라 낮은 주파수 대역에서 전자파 차폐에 큰 효과를 나타냈다. 강섬유의 혼입률이 증가할수록 차폐율이 증가하였으며 강섬유를 1.5% 혼입한 변수에서 철근 간격의 감소로 인한 차폐율 증가를 나타냈다. In this study, experimental tests were performed to determine the electromagnetic shielding characteristics of reinforced concrete based on the thickness of concrete and rebar. In addition, the electromagnetic shielding characteristics based on the steel-fiber volume ratio and rebar spacing of fiber-reinforced concrete were evaluated. Concrete showed significant Shielding Effectiveness (SE) in a high-frequency band with increasing thickness, but the rebar exhibited significant SE in the low-frequency band with increasing diameter, decreasing rebar spacing, and increasing layer. The SE increased with the steel fiber volume ratio, and it also increased owing to the decrease in the rebar spacing for 1.5 vol.% steel fibers.
전기로 산화슬래그 혼입 고강도 콘크리트의 미세구조 및 자기센싱 특성 평가
홍세희(Hong, Sehee),원천봉(Yuan, Tianfeng),최진석(Choi, Jinseok),윤영수(Yoon, Youngsoo) 한국방재학회 2019 한국방재학회논문집 Vol.19 No.5
This study analyzes the microstructure and strength properties of high-strength concrete containing electric-arc-furnace oxidizing slag (ES). Thus, three different water-to-binder ratios and four different ES-replacement ratios were considered while evaluating the hydration products of the specimens, their porosity, pore-size distribution, and compressive and splitting tensile strengths, depending on the curing age. According to the x-ray diffraction (XRD) patterns, the ES specimens of both portlandite and hatrurite exhibited higher peak intensities than those of the plain specimen (High-strength concrete, i.e., HSC). Further, from the results of the mercury intrusion porosimetry (MIP) test, it was observed that the cumulative pore volume of the ES specimens was higher than that of the HSC. Also, the porosity of the ES specimen, whose ES-replacement ratio was 20%, was approximately 37.9% higher than that of the HSC. The compressive strength and splitting tensile strength of the ES specimens significantly decreased when the ES-replacement ratio was 20%, while the best self-sensing properties were exhibited. From all the experiments, it was observed that an ES-replacement ratio of 15% exhibited similar microstructure and strength properties to those of the HSC.
Mitigating shrinkage cracking in posttensioning grout using shrinkage-reducing admixture
Yoo, Doo-Yeol,Ryu, Gum-Sung,Yuan, Tianfeng,Koh, Kyung-Taek Elsevier 2017 Cement & concrete composites Vol.81 No.-
<P><B>Abstract</B></P> <P>This study aims to reduce the cracking potential of posttensioning high-performance grout (HG) through use of shrinkage-reducing admixture (SRA). With this regard, an HG mixture was initially developed to possess appropriate fluidity with low bleeding and settling. Various amounts of SRA were subsequently incorporated into the developed HG mixture at 1% and 2% by weight to the cementitious components. A widely used ordinary grout (OG) mixture was also considered for comparison. Test results indicated that the HG mixture exhibited similar flowability to the OG mixture, while imparting much better performance with regard to strength, bleeding, and settling. The addition of SRA to the HG mixture led to higher compressive and tensile strength values after 28 days, lower shrinkage strain, lower maximum internal temperature due to hydration heat, and delayed shrinkage cracking. On the other hand, the degree of restraint due to an uneven surface of duct and the filling capacity of the HG were insignificantly affected by the inclusion of the SRA. Complete filling of ducts was observed for the HG samples. The OG mixture exhibited the smallest shrinkage strain and the best performance with regard to shrinkage cracking resistance; however, the OG mixture resulted in insufficiently filled ducts, leading to atmospheric exposure of prestressing strands. Consequently, the HG mixture with 2% SRA was proposed to be most appropriate for posttensioning grout with regard to the several properties denoted above.</P>
피난 시뮬레이션과 BIM모델을 활용한 경전철 역사 내의 ‘시설물 내 대피시설’ 위치 선정에 대한 연구
김영휘(Kim Younghwi),이진영(Lee Jinyoung),Yuan Tianfeng,윤영수(Yoon Youngsoo) 한국방재학회 2018 한국방재학회지 Vol.18 No.4
우리나라는 세계 유일의 분단국가로서 발생 가능한 잠재적인 위험에 대해 사전에 대비하고 준비할 필요성이 있다. 이러한 상황에서 단순히 대피시설의 수를 늘리기보다는, 기존 시설물을 활용하여 평상시에는 일반 용도로 사용되나 CBRE 상황에서는 대피시설로서의 기능을 할 수 있는 SIP를 확립하고 관리할 필요가 있다. 따라서 본 연구에서는 BIM 소프트웨어를 이용하여 경전철 역사를 모델링하고, 각 공간의 접근성과 수용성을 고려한 피난 시뮬레이션을 실시하여, 역사 내에 SIP의 최적 위치를 선정하는 과정을 제시하였다. 본 연구에서 제안된 과정은 직접적인 시뮬레이션을 통한 합리적인 인간 행동 분석에 기초한 것이기 때문에, 기존의 사회기반시설에 적용된다면 CBRE 상황 발생 시 더욱 안전하고 신속한 대피가 가능할 것으로 기대된다. As the only divided country, preparing for possible risks is to be considered in Korea. In these circumstances, rather than just increasing the number of evacuation facilities, it is needed to establish and manage SIP, the space that is used for its original purpose in normal situation but can be utilized as a shelter during CBRE situation. Therefore, in this study, light rail station is modeled by using BIM software and the process of selecting the best location of SIP in the station by performing several simulations accordance with various escape scenarios was presented. Since the process proposed in this study is based on rational analyses of human behavior through direct simulations, if applied to various infrastructures, it is expected for people to evacuate fast and safely under CBRE situation.