• Earthquakes and Structures
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• 제18권1호
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• pp.113-127
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• 2020

In this study, the behavior of external beam-column joints reinforced by plain and deformed bars with non-seismic reinforcement details is investigated and compared. The beam-column joints represented in this study include a benchmark specimen by seismic details in accordance with ACI 318M-11 requirements and four other deficient specimens. The main defects of the non-seismic beam-column joints included use of plain bar, absence of transverse steel hoops, and the anchorage condition of longitudinal reinforcements. The experimental results indicate that using of plain bars in non-seismic beam-column joints has significantly affected the failure modes. The main failure mode of the non-seismic beam-column joints reinforced by deformed bars was the accumulation of shear cracks in the joint region, while the failure mode of the non-seismic beam-column joints reinforced by plain bars was deep cracks at the joint face and intersection of beam and column and there was only miner diagonal shear cracking at the joint region. In the other way, use of plain bars for reinforcing concrete can cause the behavior of the substructure to be controlled by slip of the beam longitudinal bars. The experimental results show that the ductility of non-seismic beam-column joints reinforced by plain bars has not decreased compared to the beam-column joints reinforced by deformed bars due to lack of mechanical interlock between plain bars and concrete. Also it can be seen a little increase in ductility of substructure due to existence of hooks at the end of the development length of the bars.

• 한국건축시공학회지
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• 제23권2호
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• pp.123-131
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• 2023

본 연구에서는 철근콘크리트의 피복두께, 산소확산속도, 철근직경의 총 세 가지 변수로 콘크리트 균열에 대한 해석을 실시하였다. 피복두께를 변수로 하였을 때 30, 40, 50mm의 피복두께에서 약 3년, 4년, 6년경과 후 균열이 발생하였고 산소확산속도를 변수로 하였을 때 2e-9, 2e-11, 2e-12(m²/s)의 산소확산도에서 약 4년, 5년, 10년경과 후 균열이 발생하였다. 철근직경의 경우 D10, D19, D25의 철근직경에서 약 4년, 3년, 2년경과 후 균열이 발생하였다.

• 한국지반환경공학회 논문집
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• 제9권2호
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• pp.61-65
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• 2008

본 연구에서는 PGSN(Pressurized Grouting Soil Nailing) 시스템이라는 가압 그라우팅 쏘일네일링 공법을 고안하였으며, 본 공법의 보강제의 길이변화 및 보강재의 변화 등의 설계인자에 따른 거동변화를 파악해 보기 위해 변위제어방식의 현장인발시험을 수행하였다. 본 연구에서 수행한 9차례의 현장인발시험에서 그라우트 주입비의 변화를 살펴 보기위해 계측을 수행하였으며, 단기거동특성을 평가하기 위해 일반 쏘일네일링 시스템과 비교해 보았다. 가압 그라우트 쏘일네일링 공법의 인발거동 특성을 통해, 중요한 설계인자인 주입압 및 그라우트 주입비 등의 영향을 살펴보았다. 시험 결과 가압효과에 따른 인발변형 특성은 중력식 그라우팅 쏘일네일에 비해 가압 그라우팅 쏘일네일의 경우 유발되는 변위량이 30~36% 정도 감소하였고, 보강재 변화에 따른 인발 특성을 살펴보면 이형철근에 비해 강관의 경우 유발되는 변위량이 31~32% 정도 감소하는 것으로 나타났다.

• 한국지반공학회논문집
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• 제38권9호
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• pp.53-67
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• 2022

마이크로파일은 소구경 현장타설말뚝으로, 시공방법이 간단하고 공사비용이 상대적으로 저렴하여 건축물을 비롯한 각종 구조물의 보수보강 및 증축 시 기초보강 등에 활용되고 있다. 시공이 용이하고 간단한 메커니즘의 구조체를 선단에 장착하여 지지력을 증대시키는 선단 확장형 마이크로파일이 개발되었으며, 이에 대한 수치해석, 내구성시험, 원심모형시험 등의 연구가 수행되어 왔다. 본 연구에서는, 기존에 수행된 수치모델링을 고도화하여 연직하중 재하에 의해 연결강봉 근입 시 고정 지압구가 활착되는 거동 메커니즘을 확인하고, 원심모형실험과 동일한 조건에서의 수치해석을 수행하여 그 결과를 비교하였다. 또한, Lab-scale 수치해석 결과를 바탕으로 고정 지압구의 형상 개선안을 도출하고, Field-scale 수치해석을 통해 일반 마이크로파일 대비 지지력 증대효과를 비교·검증하였다.

• 한국안전학회지
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• 제27권2호
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• pp.78-83
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• 2012

This is a study to confirm how to improve and substitute the existing re-bar with other material such as a fiber rope, especially super fiber rope having much more strong tensile strength. 6(b) different fiber rope reinforced beam with a section of $20{\times}30cm$ have been made and tasted as variables designed in the study. The larger diameter of fiber rope, the more capacity of the beam, even though fiber reinforced beam are increased with ten(10)percent, each. Lower capacity of fiber-reinforced beam than normal RC beam has been analyzed theoretically and empirically, based on a lot of experiences of the same size beam test. Fiber rope-reinforced concrete beam does not have sufficient capacity than RC beam due to insufficient bonding capacity of fiber rope in concrete. It leads to decrease beam bearing capacity and crack around lower center of the beam. Therefore, bonding reinforcement of fiber rope beam such as pinning a triangles steel pin in each knot of fiber rope contributes to improving bearing capacity of fiber rope reinforcing beam.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.329-332
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• 1999

The crack of concrete induced by the heat of hydration is a serious problem, particularly in concrete structures such as underground box structure, mat-slab of nuclear reactor buildings, dams or large footings, foundations of high rise buildings, etc.. As a result of the temperature rise and restriction condition of foundation, the thermal stress which may induce the cracks can occur. Therefore the various techniques of the thermal stress control in massive concrete have been widely used. One of them is prediction of the thermal stress, besides low-heat cement which mitigates the temperature rise, pre-cooling which lowers the initial temperature of fresh concrete with ice flake, pipe cooling which cools the temperature of concrete with flowing water, design change which considers steel bar reinforcement, operation control and so on. The objective of this paper is largely two folded. Firstly we introduce the cracks control technique by employing low-heat cement mix and thermal stress analysis. Secondly it show the application condition of the cracks control technique like sidewall of LNG in Inchonl.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.293-298
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• 1999

The crack of concrete induced by the heat of hydration is a serious problem, particularly in concrete structures such as underground box structure, mat-slab of nuclear reactor buildings, dams or large footings, foundations of high rise buildings, etc.. As a result of the temperature rise and restriction condition of foundation, the thermal stress which may induce the cracks can occur. Therefore the various techniques of the thermal stress control in massive concrete have been widely used. One of them is prediction of the thermal stress, besides low-heat cement which mitigates the temperature rise, pre-cooling which lowers the initial temperature of fresh concrete with ice flake, pipe cooling which cools the temperature of concrete with flowing water, design change which considers steel bar reinforcement, operation control and so on. The objective of this paper is largely two folded. Firstly we introduce the cracks control technique by employing low-heat cement mix and thermal stress analysis. Secondly it show the application condition of the cracks control technique like the subway structure in Seoul.

• Smart Structures and Systems
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• 제31권5호
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• pp.517-529
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• 2023

Using a device composed of two lateral pressure plates (LPPs) and a steel reinforcement bar to apply horizontal pressure on slope surfaces, a newly developed prestress-reinforced embankment (PRE) is proposed, to which can be adopted in strengthening railway subgrades. In this study, an analytical model, which is available of calculating additional confining stress (σ_H) at any point in a PRE, was established based on the theory of elasticity. In addition, to verify the proposed analytical model, three dimensional (3D) finite element analyses were conducted and the feasibility in application was also identified and discussed. In order to study the performance of the PRE, the propagation of σ_H in a PRE was analyzed and discussed based on the analytical model. For the aim of convenience in application, calculation charts were developed in terms of three dimensionless parameters, and they can be used to accurately and efficiently predict the σ_H in a PRE regardless of the embankment slope ratio and LPP side length ratio. Finally, the potential applications of the proposed analytical model were discussed.

• Computers and Concrete
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• 제31권6호
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• pp.527-536
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• 2023

Fiber Reinforced Polymer (FRP) bar has emerged as a viable and sustainable replacement to steel in reinforced concrete (RC) under severe corrosive environment. The behavior of concrete columns reinforced with FRP bars, spirals, and hoops is an ongoing area of research. In this study, 3D nonlinear numerical modelling of circular concrete columns reinforced with Glass Fiber Reinforced Polymer (GFRP) bars and transversely confined with GFRP spirals were conducted using fracture-plastic model. The numerical models and experimental results are found to be in good agreement. The effectiveness of confinement was accessed through von-mises stresses, and it was found that the stresses in the concrete's core are higher with a 30 mm pitch (46 MPa) compared to a 60 mm pitch (36 MPa). The validated models are used to conduct parametric studies. In terms of axial load carrying capacity and member ductility, the effect of concrete strength, spiral pitch, and longitudinal reinforcement ratio are thoroughly investigated. The confinement effect and member ductility of a GFRP RC column increases as the spiral pitch decreases. It is also found that the confinement effect and member ductility decreased with increase in strength of concrete.

• Structural Engineering and Mechanics
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• 제84권4호
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• pp.531-546
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• 2022

Headed bars are often used when there is insufficient space for a straight or curved bar to be fully developed to ensure the transference of forces between steel and concrete in several types of connections between structural members. In such cases, the concrete breakout strength of the headed bars can be a critical point of the design and must be considered appropriately. This paper evaluates the tensile strength of headed bars embedded in reinforced concrete members, failing due to concrete breakout. Four experimental tests on headed bars embedded in slender concrete members are presented and discussed, showing that strength previsions from the design codes can be significantly conservative as they ignore the contribution from the flexural reinforcement. 3D finite element models were developed using Abaqus Unified FEA to simulate the tested specimens, and it was observed that they were able to reproduce the formation of the concrete cone accurately, besides the response and resistance observed in tests. Furthermore, the experimental, numerical, and design code resistances are compared and discussed. A new equation to evaluate the concrete cone strength of the tested headed bars is proposed, which takes into account parameters not explicitly considered in the current design equations.