• 한국구조물진단유지관리공학회 논문집
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• 제15권1호
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• pp.263-270
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• 2011

이 연구에서는 프리캐스트 콘크리트용으로 공장에서 생산되며 그 동안 국내에서 많이 사용되어온 음이온계 계면활성제의 일종인 나프탈렌 설폰산염계(Poly-Naphthalene Sulfonate Type) 혼화제와 국내 J사에서 개발된 조강형 폴리카본산계(Polycarboxilic Type) 혼화제인 WF2000의 성능을 평가하였다. 실험결과에 의하면, WF2000은 PNS계보다 20% 줄어든 사용량에도 제품이 가지고 있는 높은 감수율과 고온에서 콘크리트 응결의 촉진효과 및 우수한 분산작용으로 인하여 작업성의 개선되었으며 PHC 파일의 조기강도와 장기강도 발현에 유리하였다. 그리고 감수력과 유지력의 조절이 가능하여 원재료의 변동 및 환경조건의 변화에 적절한 대응이 가능한 혼화제로 하절기의 생산성과 작업성 저하 그리고 성형성 불량의 문제 및 동절기의 응결지연으로 인한 조기강도의 저하에 대한 문제 해결 등에 유리하였다.

• 한국환경생태학회지
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• 제18권4호
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• pp.359-368
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• 2004

본 연구는 최근 자연체험형 여가휴양 공간으로 이용이 커지고 있는 도시자연공원 탐방로의 분포와 훼손특성을 파악하여 향후 자연보전형 탐방로 정비의 방향을 설정하기 위한 기초 자료 제시를 목적으로 수행하였다. 연구대상지는 계양공원, 백마공원, 약사공원, 문학공원, 청 량공원이었다. 이들 공원은 인천시 남북녹지축에 위치하여 도시생태계 보전의 핵심지역이 되고 있는 산지형 도시자연공원이며 등반형 탐방이 많이 일어나는 곳이다. 주 탐방 노선수는 계양공원 42개, 백마공원 43개, 약사공원 9개, 문학공원 28개, 청량공원 22개로서 면적에 비해 과도한 탐방로가 있었으며 샛길이 늘어나고 있는 것으로 추측되었다. 연구대상지 탐방로의 평균 나지노폭은 3.5m, 평균 최대침식 깊이는 21.3cm로 나타났고 체계적인 정비가 없을 경우 훼손은 급격히 증가될 것으로 판단되었다. 훼손이 심해 복구가 요구되는 산림환경피해도 등급 5, 6등급의 비율은 19.6∼78.0%에 달했다. 연구결과에 기초하여 인천 남북녹지축상의 산지형 도시자연공원 탐방로의 정비와 관리방안을 제안하였다.

• Steel and Composite Structures
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• 제21권2호
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• pp.357-371
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• 2016

Column base connections are critical components in steel structures because they transfer axial forces, shear forces and moments to the foundation. Exposed column bases are quite commonly used in low- to medium-rise buildings. To investigate shear transfer in exposed column base plates, four large scale specimens were subjected to a combination of axial load (compression or tension) and lateral shear deformations. The main parameters examined experimentally include the number of anchor rod, arrangement of anchor rod, type of lateral loading, and axial force ratio. It is observed that the shear resisting mechanism of exposed column base changed as the axial force changed. When the axial force is in compression, the resisting mechanism is rotation type, and the shear force will be resisted by friction force between base plate and mortar layer. The specimens could sustain inelastic deformation with minimal strength deterioration up to column rotation angle of 3%. The moment resistance and energy dissipation will be increased as the number of anchor rods increased. Moreover, moment resistance could be further increased if the anchor rods were arranged in details. When the axial force is in tension, the resisting mechanism is slip type, and the shear force will be resisted by the anchor rods. And the shear resistance was reduced significantly when the axial force was changed from compression to tension. The test results indicated that the current design approach could estimate the moment resistance within reasonable acceptance, but overestimate the shear resistance of exposed column base.

• Computers and Concrete
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• 제26권2호
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• pp.115-125
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• 2020

To reduce the damage of concrete in fire, a new type of lightweight cinder aggregate concrete was developed due to the excellent fire resistance of cinder. To further enhance its fire resistance, Polypropylene (PP) Fibers which can enhance the fire resistance of concrete were also used in this type of concrete. However, the bond behavior of this new type of concrete after fire exposure is still unknown. To investigate its bond behavior, 185 specimens were heated up to 22, 200, 400, 600 or 800℃ for 2 h duration respectively, which is followed by subsequent compressive and tensile tests at room temperature. The concrete-rebar bond strength of C30 PP fiber-reinforced cinder concrete was subsequently investigated through pull-out tests after fire exposure. The microstructures of the PP fiber-reinforced cinder concrete and the status of the PP fibre at different temperature were inspected using an advanced scanning electron microscopy, aiming to understand the mechanism of the bonding deterioration under high temperature. The effects of rebar diameter and bond length on the bond strength of PP fiber-reinforced cinder concrete were investigated based on the test results. The bond-slip relation of PP fiber-reinforced cinder concrete after exposure at different temperature was derived based on the test results.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.549-552
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• 2006

Generally the ultra-high strength steel reinforced concrete has rich mix composition composed of high-strength type mineral admixtures and as a result of very low water-binder ratio(about under w/b=25%), it reveals ultra-high compressive strength(about over 100Mpa). Also, in order to obtain sufficient toughness after construction, we usually mix a large quantity steel fiber with ultra-high strength steel reinforced concrete therefore we must use proper mixer for workability. When we make the ultra-high strength steel reinforced concrete we need more long mixing time or much super-plasticizer than when we manufacture normal concrete. These bring about economical problems and performance deterioration. Therefore, in this study, in order to manufacture easily ultra-high strength steel reinforced concrete we develope a dedicated mixer for ultra-high strength steel reinforced concrete with high speed type. It carried out the examination for comparison between the dedicated and general type mixer, the analysis and counterplan of the point at issue when we manufacture ultra-high strength steel reinforced concrete by the dedicated mixer.

• 폴리머
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• 제26권2호
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• pp.193-199
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• 2002

전보에서 합성한 디클로로-폴리에스테르 폴리올(DCBAO)에 2종류의 이소시아네이트 경화제인 Desmodur N-3300과 Desmodur L-75를 선택하여 상온경화시켜 PU계 난연도료 (DCBAO/N-3300=DCBAN 및 DCBAO/L-75=DCBAL)를 각각 제조하였다. 제조된 DCBA과 DCBAL 도료로서 도막물성을 측정한 결과, 양쪽 모두의 도료가 난연처리 후에도 물성저하 현상을 초래하지 않았으며, 별도의 황변성 시험에서 황변성은 DCBAL 쪽이 다소 불량하게 나타나 Desmodur L-75가 황변성과 관련이 있음을 알았다. 또한 난연성분인 2,4-dichlorobenzoic acid의 함량 20∼30 wt%에서 LOI 값 25∼26% 선의 난연효과를 보여주었다.

• KIEAE Journal
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• 제4권4호
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• pp.35-44
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• 2004

In Korea, the apartment buildings have been constructed recently in large quantities to provide housing due to the gravitation of population towards large cities. However, because of this trend toward high-rise apartment, a number of problems are occurred such as the deterioration of comfort in the dwelling environment and the lack of solar access right in apartment buildings. In the building law, the sunshine hour and the minimal separated distance between apartment buildings as regulated as the criteria for the site planning. Most of site planners, however, designed the apartment site only following minimum separated distance. As a result, the problem of sunshine hours lack is caused and legal dispute concerning solar access right is also arisen. The purpose of this study is to improve solar access right regulation and to help site design of apartment planning. Accordingly, we execute empirical analysis based on computer simulation in order to find suitable separated distance between typically designed apartment buildings. First, we estimated sunshine hours according to independent building orientation, height, and length. Second, we calculated sunshine hours in various case of apartment arrangement; parallel type, courtyard type, tower type and etc. with various separated distance.

• 한국공간구조학회논문집
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• 제17권2호
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• pp.53-62
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• 2017

This study aims to establish a seismic resistance performance evaluation method that makes sure to secure the seismic resistance performance of the existing mid-low story reinforced concrete structures. This study focuses on the development of the seismic resistance performance evaluation method for the overall seismic resistance performance evaluation on the buildings by applying fuzzy theory. This seismic resistance performance evaluation method considers the mutual relations among the type of force, the type of member, the type of story, and the states of deterioration of the buildings. The total seismic resistance performance index from this method was calculated by the intensity weight of each evaluation item, fuzzy measure, fuzzy integration. Moreover, the evaluation methodology was established in this study to identify the performance level of the Immediate Occupancy, Life Safe, Collapse Prevention by applying the fuzzy theory.

• Smart Structures and Systems
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• 제17권1호
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• pp.45-58
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• 2016

Freezing and thawing cycles induce deterioration and strength degradation of concrete structures. This study presumes that a large quantity of contact-type defects develop due to the freezing and thawing cycles of concrete and evaluates the degree of defects based on a nonlinearity parameter. The nonlinearity parameter was obtained by an impact-modulation technique, one of the nonlinear ultrasonic methods. It is then used as an indicator of the degree of contact-type defects. Five types of damaged samples were fabricated according to different freezing and thawing cycles, and the occurrence of opening or cracks on a micro-scale was visually verified via scanning electron microscopy. Dynamic modulus and wave velocity were also measured for a sensitivity comparison with the obtained nonlinearity parameter. The possibility of evaluating strength degradation was also investigated based on a simple correlation of the experimental results.

• 한국산업융합학회 논문집
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• 제26권1호
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• pp.175-181
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• 2023

In offshore plants, various equipments including cranes and davits are used for safety management. Hydraulic cylinder type actuators are mainly used for luffing operations such as cranes and davits. However, in the case of a cylinder using hydraulic pressure, a separate power pack is required to supply hydraulic pressure. When used for a long time, maintenance costs such as sticking of hydraulic valves, contamination of hydraulic oil and deterioration of hydraulic hoses occur. In addition, a lot of hydraulic oil is used in the handling of cranes and davits, which causes marine pollution due to management problems. As a result, as interest in marine pollution prevention has increased recently, interest in actuators that do not use hydraulic pressure is also increasing. Therefore, in this study, we intend to develop a davit with an electric cylinder type actuator that uses electricity rather than hydraulic pressure by the SOLAS regulation. In other words, the conceptual design of the davit driven through the linear motion of the ball screw using electricity is performed, and the structural safety of the drive is also reviewed so that it can be utilized in the industrial field.