• 한국구조물진단유지관리공학회 논문집
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• 제18권1호
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• pp.10-18
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• 2014

못과 앵커를 이용하여 FRP를 콘크리트에 부착시키는 MF-FRP 공법은 에폭시를 이용하여 콘크리트 구조물을 보강시키는 외부 부착 FRP 보강 공법에 비하여 더 많은 연성을 부여하는 것으로 많은 연구를 통하여 확인되었다. 이러한 MF-FRP 공법의 사용은 앞으로 증가할 것으로 예상된다. 그러나 MF-FRP 보강법의 환경영향에 대한 평가에 대해서는 현재 연구가 전무한 상태이다. 본 연구에서는 환경의 영향으로부터 MF-FRP 구조물이 구조건전성을 유지할 수 있는지 6개월의 기간 동안 환경조건을 구성하여 보강보의 거동을 비교 평가하였다. RC보에 MF-FRP 보강 공법을 적용시킨 후 지속하중을 가하는 조건과 함께 서중온도 ($40^{\circ}C$) 및 외기환경 조건에 6개월 (10월-3월)의 동절기 기간 동안 보강보를 노출시켰다. 이후 4점 휨실험을 수행하여 각 시험체의 구조건전성을 평가한 결과 본 연구에서 제시한 환경 조건에서는 MF-FRP 보의 강성 변화나 파괴모드의 변화가 발생하지 않아 구조건전성이 유지되는 것으로 나타났다. 보의 파괴모드는 FRP의 박리와 콘크리트의 파쇄에 의해 결정적인 영향을 받으며 못과 앵커로만 연결된 FRP와 콘크리트의 부착성능은 파괴모드에 영향을 주지 못하는 것으로 나타났다.

• Structural Engineering and Mechanics
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• 제73권3호
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• pp.239-257
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• 2020

In the present study, an innovative steel bracket and haunch hybrid scheme is devised, for retrofitting of earthquake damaged deficient beam-column sub-assemblages. Formulations are presented for evaluating haunch force factor under combined load case of lateral and gravity loads for the design of double haunch retrofit. The strength hierarchies of control and retrofitted beam-column sub-assemblages are established to showcase the efficacy of the retrofit in reversing the undesirable strength hierarchy. Further, the efficacy of the proposed retrofit scheme is demonstrated through experimental investigations carried out on gravity load designed (GLD), non-ductile and ductile detailed beam-column sub-assemblages which were damaged under reverse cyclic loading. The maximum load carried by repaired and retrofitted GLD specimen in positive and negative cycle is 12% and 28% respectively higher than that of the control GLD specimen. Further, the retrofitted GLD specimen sustained load up to drift ratio of 5.88% compared with 2.94% drift sustained by control GLD specimen. Repaired and retrofitted non-ductile specimen, could attain the displacement ductility of three during positive cycle of loading and showed improved ductility well above the expected displacement ductility of three during negative cycle. The hybrid haunch retrofit restored the load carrying capacity of damaged ductile specimen to the original level of control specimen and improved the ductility closer to the expected displacement ductility of five. The total cumulative energy dissipated by repaired and retrofitted GLD, non-ductile and ductile specimens are respectively 6.5 times, 2.31 times, 1.21 times that of the corresponding undamaged control specimens. Further, the damage indices of the repaired and retrofitted specimens are found to be lower than that of the corresponding control specimens. The novel and innovative steel bracket and haunch hybrid retrofit scheme proposed in the present study demonstrated its effectiveness by attaining the required displacement ductility and load carrying capacity and would be an excellent candidate for post-earthquake retrofit of damaged existing RC structures designed according to different design evolutions.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 가을 학술발표회 논문집
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• pp.285-292
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• 2000

Though there has been increasing use of large diameter drilled shaft as a foundation structure of bridges, current practice for quality control is to confirm the minimum required load carrying capacity during construction stage. For economic and appropriate design of drilled shaft, it is necessary to evaluate the load transfer mechanism by pile load tests during initial stage of construction and to use the test results as a feedback to a revision of initial design. In this paper, results of load tests peformed at several domestic sites are presented to investigate the load transfer characteristics of large diameter drilled shaft. It was found that most of the load on piles is sustained by shaft friction and that only small portion of the load reaches the bottom of the drilled shaft. Some test results of drilled shaft by Pile Driving Analyzer performed at same sites are also presented to compare the load transfer characteristics interpreted from static pile load tests.

• Investigative Magnetic Resonance Imaging
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• 제21권4호
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• pp.199-209
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• 2017

Purpose: Caffeine is the most widely consumed psychostimulant. It is often adopted as a tool to modulate brain activations in fMRI studies. However, its pharmaceutical effect on task-induced deactivation has not been fully examined in fMRI. Therefore, the purpose of this study was to examine the effect of caffeine on both activation and deactivation under sustained attention. Materials and Methods: Task fMRI was acquired from 26 caffeine naive healthy volunteers before and after taking caffeine pill (200 mg). Results: Statistical analysis showed an increase in cognition-load dependent task activation but a decrease in load dependent de-activation after caffeine ingestion. Increase of attention and memory task activation and its load-dependence suggest a beneficial effect of caffeine on the brain even though it has no overt behavior improvement. The reduction of deactivation by caffeine and its load-dependence indicate reduced facilitation from task-negative networks. Conclusion: Caffeine affects brain activity in a load-dependent manner accompanied by a disassociation between task-positive network and task-negative network.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.790-793
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• 2001

The characteristics of smart skin for wireless LAN system under compression load are investigated. The smart skin structure is composed of 3 layers of face material and 2 layers of core material. Theoretical formula for determining buckling load is derived by Rayleigh-Ritz method and compared with experimental result. The maximum length of specimen that buckling does not occur is determined by assuming that the compression load is sustained by only face material. In the experiment, if buckling occurs obviously then it follows the theoretical result well. In the process of buckling, the load supporting capability and the antenna property such as radiation pattern and reflection coefficient were examined.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.319-322
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• 2005

When a concrete structure is subjected to load, its response is both immediate and time dependent. Under sustained load, the deformation of a structure gradually increases with time and eventually may be many time greater than its instantanneous value. The gradual development of strain with time is caused by creep and shrinkage. On this study, to estimate of stress variations on time effects in partially prestressed concrete composite girder bridges, computer program applied Age-adjusted Effective Modulus Method(AEMM) in used.

• 전기학회논문지P
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• 제65권3호
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• pp.178-182
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• 2016

FIDVR(Fault Induced Delayed Voltage Recovery) is a phenomenon that recovery of the system voltage level delays after the fault. Cause of FIDVR phenomenon is motor load characteristic about voltage and reactive power. In low voltage condition, the motor go to stall state that consume large amount of reactive power. As a result, the voltage recovery problem is that of repeated occurrences of sustained low voltage following faults on the system. In this paper, analysis the characteristics of the motor load. And using the korean power system actual data, perform a case studies to voltage delay recovery phenomenon alleviation method. Change of each parameters by analyzing the effect on system and selecting an influence parameter. In addition, dynamic characteristic analysis of the resulting difference in the proportion by the motor load in power systems, considering the effect on the voltage stability.

• 한국지반신소재학회논문집
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• 제4권2호
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• pp.29-38
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• 2005

토목합성 보강재를 이용한 보강토 공법을 도로 혹은 철도구조물 등 영구 구조물에 적용하기 위해서는 지속하중 및 반복하중이 작용하는 보강토 구조물의 장기변형 특성을 이해하고 이를 설계/시공에 반영하는 것이 필요하다. 본 논문에서 실대형 지오그리드 보강토 옹벽에 포설된 지오그리드의 유발 인장변형율에 대한 장기계측 결과를 토대로 장기거동 특성을 분석하였다. 3년여에 걸친 계측결과를 분석한 결과 보강토 옹벽에 포설된 보강재의 유발 인장 변형율은 시공완료후 지속적으로 증가하는 경향을 보였으며 전반적으로 응력이 집중되는 위치에 포설된 보강재의 증가가 뚜렷하게 관찰되었다. 러한 결과로부터 중요 구조물의 일부로 시공되는 보강토 옹벽의 설계/시공시에는 장기변형에 대한 고려가 필요한 것으로 나타났다.

• 한국지반신소재학회논문집
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• 제10권4호
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• pp.105-112
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• 2011

본 논문에서는 지속하중이 작용하는 보강토 구조물의 시간의존적 장기거동에 관한 수치 모델링 기법을 다루었다. 먼저 Power Law 기반의 크리프 모델을 이용하여 지오그리드와 뒤채움흙의 크리프 거동의 모델링에 대한 적용성을 검토 하였으며 나아가 보강토 교대 구조물의 장기 거동에 대한 해석에 적용하였다. 그 결과 Power Law 기반의 크리프 모델은 지오그리드와 뒤채움흙으로 구성되는 보강토 교대 구조물에 지속하중 작용시 발생하는 크리프 변형을 적절히 모사할 수 있는 것으로 검토되었으며 크리프 변형이 발생할 수 있는 뒤채움흙을 사용하는 경우 교대 벽체 및 상판기초에 허용치를 초과하는 변위가 발생할 수 있는 것으로 검토되었다. 본 연구에서 얻어진 결과의 실무적 적용 방안에 대한 내용을 기술하였다.

• Steel and Composite Structures
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• 제39권2호
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• pp.159-170
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• 2021

Concrete filled steel tubes (CFSTs) are extensively used in a variety of structures due to their structural and economic advantages over other types of structures. Considerable research has been conducted with regards to their short-term behaviour, and very limited studies have focused on their long-term behaviour. In this study, a series of tests were carried out on high strength squat (short) CFSTs and concrete cylinders under controlled conditions of temperature and humidity to better understand their time dependent behaviour. A number of parameters were investigated including the influence of steel and concrete bond, confinement, level of sustained load and sizes of specimens. The results revealed that creep strains increased by more than 40% if there was no bonding between steel tube and concrete core. As expected, creep and shrinkage of concrete inside a steel tube were significantly less than those developed in exposed concrete. At the end of a creep period of six months, all the specimens were tested to failure to observe the influence of sustained loads on the ultimate strength. It was found that creep does not have a major effect on the strength of short CFSTs in the specific experimental study conducted here, which was less than 2.5%.