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철근콘크리트 보의 간접 균열제어를 위한 최대 철근간격 제안
이기열(Lee Kiyeol),이민희(Lee Minhi) 한국방재학회 2018 한국방재학회논문집 Vol.18 No.6
이 논문은 철근콘크리트 보의 균열폭을 직접 계산하지 않고 사용성능을 검토할 수 있는 간접균열제어의 방법인 최대 철근간격을 철근응력 수준별로 새롭게 제안한 것이다. 균열폭 이론에 기반한 계산식에 철근과 콘크리트의 부착특성과 균열거동을 반영한 균열간격 및 인장강화효과를 이용하여 철근간격을 계산할 수 있는 식을 유도하였다. 이 식으로부터 사용하중에 따른 철근응력 수준별로 단면깊이의 변화에 영향을 받지 않는 최대 철근간격을 새롭게 산정하였다. 이와 함께 콘크리트 압축강도의 증가를 반영할 수 있는 보정계수를 추가적으로 제안하였다. 제안된 최대 철근간격은 복잡한 균열폭 계산식을 대체할 수 있으며, 간접균열제어에 의한 철근콘크리트 보의 사용성능 검토의 적용성을 개선하였다. This paper proposes a maximum bar spacing according to the steel stress level as an indirect crack control for the verification of serviceability performance without calculating the crack width in a reinforced concrete beam. Based on the crack width theory, a new formulation that can calculate the bar spacing using the crack spacing and tension stiffening effect was derived by considering the bond characteristics and cracking behavior. From this equation, the maximum bar spacing, which is not affected by the change in section height, was newly calculated for each level of steel stress according to the service load. In addition, a correction factor was proposed to consider the increase in concrete strength. The proposed maximum bar spacing can replace the complex crack width calculation and improve the application and serviceability performance of reinforced concrete beams through indirect crack control.
차량 안정성 관련 Fe-Mn-Si-C계 TRIP형 복합조직강의 화학조성에 따른 인장특성
이기열(Kiyeol Lee),김덕환(Duckwhan Kim),김재철(Jaechul Kim),심주현(Joohyun Shim),황종원(Jongwon Hwang),백일기(Ilki Baik) 한국자동차공학회 2006 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
The effect of chemical compositon on the microstructural change and tensile property in TRIP-assisted steels with different chemical composition was investigated by using SEM, TEM, XRD and UTM. As a result of microscopic observation, the morphology of retained austenite could be identified as two types : a granular type in a steel containing higher Si and a film type in a steel having higher C. For the case of higher C-containing steel with a tensile strength of 860 ㎫ and a total elongation of 38%, film-typed retained austenite could be observed between lath bainitic ferrite. Actually, metastable retained austenite was a requisite for the good formability, which means that chemical composition plays a significant role in the microstructure and tensile property of TRIP-assisted steels. With respect to tensile property, the steels containing suitable Si and Mn, respectively, showed a typical TRIP effect in stress-strain curve, while a steel containing higher Mn content exhibited the as similar behavior shown in dual phase steel.
자동차구조용 TRIP형 복합조직강의 베이나이트 변태특성에 미치는 어닐링 처리조건의 영향
이기열(Kiyeol Lee),최해수(Haesoo Choi),김태훈(Taehun Kim),윤태삼(Taesam Yoon) 한국자동차공학회 2010 한국자동차공학회 학술대회 및 전시회 Vol.2010 No.11
A combination of elongation and high strength is achieved in process of a TRIP-assisted multiphase steel (Fe-Mn-Si-C) by intercritical annealing and then rapid cooling into bainite transformation temperature range to hold several minutes. This combination is caused by TRIP(TRansformation Induced Plasticity) of retained austenite. For this research, the TRIP-assisted steels with different chemical compositions were annealed for a range of variable time (5 min. ~ 40 min.) in austenite single region to clarify the effect of annealing treatment condition on the mechanical property and retained austenite characteristics. As a result of microscopic observation (transmission electron microscopy), the morphology of retained austenite could be identified as two typer : a granular type and film type. Actually, suitable volume fraction of metastable austenite was a requisite for the good formability necessarily required as a principle mechanical property in automobile industry. For the case of HC steels showing a tensile strength of 860 ㎫ and a total elongation of 38 %, film typed reatained austenite could be observed between lath bainitic ferrite.
장수풍뎅이 유충 추출물이 사염화탄소에 의한 마우스의 간 손상에 미치는 영향
최용화(Yong Hwa Choi),이기열(Kiyeol Lee),양경미(Kyung Mi Yang),정윤미(Yun Mi Jeong),서정숙(Jung Sook Seo) 한국식품영양과학회 2006 한국식품영양과학회지 Vol.35 No.10
This study was conducted to investigate the effect of methanol extract of Allomyrina dichotoma larva (MEAL) on carbon tetrachloride (CCl4)-induced hepatotoxicity in mice. ICR mice were divided into 5 groups [Vehicle control, CCl4 (10 μg/g) alone, CCl4 plus a low dose (50 μg/g) of MEAL, CCl4 plus a high dose (100 μg/g) of MEAL]. Silymarin (2 μg/g) was used as the reference in the experiment. Administration of MEAL tended to decrease the serum alanine transaminase (ALT) activity induced by CCl4 treatment in mice. Hepatic concentration of thiobarbituric acid-reactive substances (TBARS) in a high-dose group of diet decreased to the level of silymarin-treated group. Hepatic activity of glutathione S-transferase in MEAL-treated group was lower than that of CCl4-treated group. Serum concentration of bilirubin was significantly increased by CCl4 treatment, but MEAL or silymarin recovered the level. These results suggest that MEAL may exert the protective effect against CCl4-induced hepatotoxicity in mice. However, more intensive studies would be needed to elucidate the protective mechanism of the beetle on hepatotoxicity of mice.