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성숙도 방법을 이용한 불포화 폴리에스터 수지 폴리머 콘크리트의 압축강도 예측
최기봉,김남길,이윤수,연규석,Choi, Ki-Bong,Jin, Nan Ji,Lee, Youn-Su,Yeon, Kyu-Seok 한국농공학회 2017 한국농공학회논문집 Vol.59 No.6
This study investigated to predict the compressive strength of unsaturated polyester resin based polymer concrete using the maturity method. The test results show that the development of the compressive strength increased exponentially until an age of 24 hours. After 24 hours, the development of the compressive strength just increased gradually. This test result shows that the strength of unsaturated polyester resin based polymer concrete was developed mainly at the early age. Estimated datum temperature of unsaturated polyester resin based polymer concrete was $-20.67^{\circ}C$ which was much lower than of datum temperature ($-10^{\circ}C$) of Portland cement concrete. Also, this study result shows that the existing maturity index associated with Portland cement concrete was not applicable for polymer concrete because curing time of Portland cement concrete is different clearly with curing time of polymer concrete. The cause of different curing time was that there were different curing mechanisms between Portland cement concrete and polymer concrete. In order to best apply the experimental data to a model, CurveExpert Professional, the commercial software, was used to determine the predictive model regarding the compressive strength of unsaturated polyester resin based polymer concrete. As a result, Gompertz Relation or Weibull Model was an appropriate model as a predictive model. The proposed model can be used to predict the compressive strength, especially, it is more useful when the maturity is in the range between $40^{\circ}C{\cdot}h^{0.4}$ and $900^{\circ}C{\cdot}h^{0.4}$.
최기봉,윤희주,차승희,최정도 ( Ki Bong Choi,Hee Ju Youn,Seung Hee Cha,Jung Do Choi ) 한국센서학회 1997 센서학회지 Vol.6 No.5
Fiber-optic evanescent wave sensor was designed and fabricated to detect mouse immunoglobulin G(IgG) with decladed optical fiber on which anti-mouse IgG was immobilized. A sensitivity obtained by any direct or competitive method was lower than 1 ㎍/㎖. Anti-mouse IgG was immobilized on 93.9% of core surface of optical fiber by simple adsoption method. The effect of postcoating using bovine serum albumin to remove non-specific binding was not observed. As the ratio of fluorescein to mouse IgG increased, the fluorescence signal increased, but that increase showed no linear relationship. Our fiber--optic sensor system could be used as immunosensor by measuring evanescent fluorescence in antigen-antibody reaction with good sensitivity below lug/mP level.
다방향성 바잘트 섬유 시트로 전단보강한 철근콘크리트 보의 전단성능
최기봉 ( Choi Ki-bong ) 한국복합신소재구조학회 2022 복합신소재구조학회논문집 Vol.13 No.5
이 연구는 다방향성 바잘트 섬유 시트로 보강한 철근콘크리트 보의 보강방법에 따른 전단거동을 실험을 통해 확인하였다. 실험변수는 보강방법(무보강, 45도 90도 U형)과 보강겹수(0, 1 2겹)를 변수로 두었으며 전단강도실험결과 바잘트섬유시트를 90도로 1겹 보강하였을 때 최대 11% 이상의 보강성능을 확인하였다. 또한, 유효변형률을 검토한 결과 섬유양이 증가함에 따라 유효변형률이 감소함을 확인하였다. The shear behavior according to the reinforcement method of concrete beams reinforced with multidirectional basalt fiber sheets was verified through experiments. The experimental parameters were the reinforcement method (non-reinforcement, 45°, 90°, and U-shaped) and the number of reinforcement layers (0, 1, and 2 layers). The shear strength test revealed an up to 11% increase in shear performance when a basalt fiber sheet was used as reinforcement in a single layer at 90°. Additionally, the effective strain decreased as the amount of FRP was increased.
최기봉 ( Choi Ki-bong ),윤현도 ( Yun Hyun-do ),최창식 ( Choi Chang-sik ),서수연 ( Seo Soo-yeon ) 한국구조물진단유지관리공학회 2005 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.9 No.1
Acoustic monitoring technique is mainly applicable to dynamic situations where processes occurring generate acoustic emission. The aim of this study was to examine the emission of acoustic signals from repaired/strengthened structure. In a structure, the energy can be detected by continuous acoustic monitoring if suitable equipment is available. The technique has also been used for this paper to detect acoustic energy emitted as concrete cracks under load. Efficient methods have been developed to accumulate and process data generated by such events as they occur. In this paper, concrete members under axial load, fatigue load and flexural load were used to evaluate cracking and failure process. AE technique was used to evaluate the characteristics of damage process and the failure mechanism of reinforced concrete beams.
최기봉 ( Choi¸ Ki Bong ),김강호 ( Kim¸ Kang Ho ),곽승택 ( Kwak¸ Seung Taek ) 한국구조물진단유지관리공학회 2000 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.4 No.2
An integrated experimental-theoretical investigation was performed on the dowel behavior at high-strength reinforced concrete in the high-rise building. Results of an experimental study on the dowel action of beam longitudinal bars at beam-column interfaces in high-strength concrete(450 ~ 600kgf/cm<sup>2</sup>) frames are presented. The crack patterns and dowel load-deflection diagrams are presented for specimens with different sizes of dowel bars. Test results indicate that the stiffness and energy dissipation capacity of dowel bars deteriorate severely with repetition of inelastic load cycles.
일부 소방공무원의 사회심리적 스트레스 및 피로수준과 관련요인
최기봉(Choi, Ki-Bong),김광환(Kim, Kwang-Hwan),조영채(Cho, Young-Chae) 한국산학기술학회 2009 한국산학기술학회논문지 Vol.10 No.4
본 연구는 일부 소방직공무원들의 스트레스 및 피로 수준을 파악하고, 스트레스와 피로에 관련된 요인을 구명하고자 청주시의 소방공무원 262명을 대상으로 구조화된 무기영 자기기입식 설문지(self-administrated questionnaire)를 이용한 설문조사를 실시하였다. 연구결과 전체 조사대상 소방공무원들의 사회심리적 스트레스 수준은 잠재적 스트레스군이 12.2%, 고위험스트레스군이 87.8% 이었으며, 건강군은 한 명도 없었다. 피로수준은 중앙값을 기준으로 구분하였을 경우, 낮은 군이 51.1 %, 높은 군이 48.9%를 차지하였다. 단계별 다변량 회귀분석 결과 사회심리적 스트레스에 영향을 미치는 요인으로는 주관적인 건강상태, 직장생활만족도, 직무요구도, 음주상태 등이 선정되었으며, 피로수준에 영향을 미치는 요인으로는 주관적 건강상태, 규칙적인 운동여부 등이 선정되었다. 이상의 연구결과는 소방공무원의 사회심리학적 스트레스나 피로수준이 대단히 높은 것을 시사하며 여러 요인들이 관여하고 있음을 알 수 있다. 따라서 소방공무원들의 스트레스나 피로를 감소시키기기 위한 건강증진프로그램의 개발 및 시행이 필요할 것으로 생각된다. The levels of psychosocial stresses and fatigue of firemen were analyzed 10 reveal the various factors related 10 them. The self-administered questionnaires were performed to 262 firemen in Cheongju City. ln terms of various levels of psychosocial stresses, 12.2% were under potential stresses, 87.8% were under high-level of stress, but healthy group was not found. The levels of fatigue symptoms divided by the median of total scores was 51.1% of low levels, and 48.9% of high levels. Multiple stepwise analysis revealed that the factors of influence on psychosocial stresses with explanatory powers of 11.5% included subjective health status, job satisfaction, job demand and alcohol drinking habits. The factors of influence on fatigue symptoms with explanatory powers of 9.0% included subjective health and regular exercises. The study results indicate that the level of stress or fatigue is so complicatedly influenced by variable factors. Thus the effective strategy for stress and fatigue reduction among firemen should include additional programs focusing on health promotion.