• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.203-208
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• 2001

Objectives of this study included design of head and evaluation of the pullout performance of the headed reinforcement that can be used to replace standard hooks in the building exterior beam-column joints. Results of 36 pullout tests are presented. Test variables included reinforcing bar diameters (16-25mm), embedment depth (6-7db), transverse reinforcement, and single-vs.-group pullout behavior. The square head designed had gross area of 4Ab and thickness of db. The headed reinforcement made of Dl6 bars developed pullout strengths close to the bar yield strength, but larger bars developed strengths smaller than the yield strengths. The pullout resistance increased with decreasing spacing of the transverse reinforcement. Use of column ties with 6.0-db spacing improved the pullout performance of the headed bars without causing difficulties in fabricating the specimens. The comparison of the pullout performances between the headed bars and the standard hooks revealed that strengths, stiffnesses, and ductile behaviors are about the same.

• 콘크리트학회논문집
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• 제15권5호
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• pp.643-649
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• 2003

본 연구의 목적은 부착실험 및 휨실험을 실시하여 구조용 합성섬유의 단면적 및 표면형상의 변화에 따른 부착성능과 휨성능을 평가하는 것이다. 6가지 다른 형상의 구조용 합성섬유를 조사하였고 부착 및 휨실험을 수행하였다. 6가지 형상의 구조용 합성섬유를 조사하였고 휨시험과 부착시험을 실시하였다. 실험변수는 3가지 종류의 형상과 2가지 종류의 단면적 변화로 하였다. 실험결과 구조용 합성섬유의 단면적이 동일할 때 주기 및 높이가 증가할수록 부착하중 및 인발 파괴 에너지는 감소하고 휨강도는 증가하였다. 또한 주기 및 높이가 일정할 섬유의 단면적이 증가할수록 인발하중과 인발 파괴 에너지는 증가하였고 휨강도는 감소하였다. 실험결과를 기본으로하여 콘크리트의 구조성능은 섬유의 부착성능 뿐만 아니라 콘크리트에 혼입되어 있는 섬유의 수, 인장하중에 저항할 수 있는 섬유의 재료특성 등에 복합적으로 영향을 받는 다는 것을 알 수 있었다.

• 한국농공학회논문집
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• 제55권3호
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• pp.113-121
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• 2013

Recently, it has been studied for the application of nano-materials in the concrete. Applied a small amount of nano-materials can achieve the goal of high strength, high performance and high durability. The small addition of nano clay improves strength, thermal stability, and durability of concrete because of the excellent dispersion. The present study has investigated the effectiveness, when varying with the contents of nano clay, influencing the pull-out behavior of macro synthetic fibers in nano materials cement mortar. Pullout tests conducted in accordance with the Japan Concrete Institute (JCI) SF-8 standard for fiber-reinforced concrete test methods were used to evaluate the pullout performance of the different nano clay. Nano clay was added to the 0, 1, 2, 3, 4 and 5 % of cement weight. The experimental results demonstrated that the addition of nano clay led to improve the pull-out properties as of the load-displacement curve in the precracked and debonded zone. Also, the compressive strength, flexural strength and pullout performance and of Mix No. 1 and No. 2 increased up to the point when nano clay used increased by 2 and 3 % contents, respectively, but decreased when the exceeded 3 and 4 %, respectively. It was proved by verifying increase of the scratching phenomenon in macro synthetic fiber surface through the microstructure analysis on the surface of macro synthetic fiber.

• 콘크리트학회논문집
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• 제22권4호
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• pp.575-583
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• 2010

이 연구는 비틀림 강섬유(T- 섬유) 의 비틀림 횟수가 인발거동과 T- 섬유를 사용한 고성능 섬유보강 시멘트 복합재료의 인장거동에 미치는 영향을 조사하였다. T- 섬유의 여러 인자와 비틀림 횟수가 섬유의 인발거동에 미치는 영향을 해석적으로 조사하고, 최대의 인발에너지를 생성할 수 있는 비틀림 횟수를 조사하였다. 이와 더불어 T- 섬유의 인발시험과 인장시험을 수행하여, 비틀림 횟수가 고인성 섬유보강 시멘트 복합재료의 인장거동에 미치는 영향을 조사하였다. 비틀림 횟수가 6ribs/30 mm인 T(L)- 섬유와 비틀림 횟수가 18ribs/30 mm인 T(H)- 섬유를 사용하였다. T(H)- 섬유는 인발시험시 섬유의 파단되어, T(L)- 섬유보다 높은 인발응력을 유발했음에도 불구하고 낮은 총 인발에너지를 생성하였다. 이러한 인발 시험서의 결과는 인장 거동에도 분명하게 반영되었다. T(L)- 섬유를 사용한 고인성 섬유보강 시멘트 복합재료의 경우, T(H)- 섬유의 사용시보다, 우수한 변형능력과 에너지 흡수능력, 그리고 미세균열 거동을 보였다.

• Geomechanics and Engineering
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• 제15권3호
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• pp.841-849
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• 2018

The purpose of a rock bolt is to improve the mechanical performance of a jointed-rock mass. The performance of a rock bolt is generally evaluated by conducting a field pullout test, as the analytical or numerical evaluation of the rock bolt behavior still remains difficult. In this study, wide range of field test was performed to investigate the pullout resistance of rock bolts considering influencing factors such as the rock type, water bearing conditions, rock bolt type and length. The test results showed that the fully grouted rock bolt (FGR) in water-bearing rocks can be inadequate to provide the required pullout resistance, meanwhile the inflated steel tube rock bolt (ISR) satisfied required pullout resistance, even immediately after installation in water-bearing conditions. The ISR was particularly effective when the water inflow into a drill hole is greater than 1.0 l/min. The effect of the rock bolt failure on the tunnel stability was investigated through numerical analysis. The results show that the contribution of the rock bolt to the overall stability of the tunnel was not significant. However, it is found that the rock bolt can effectively reinforce the jointed-rock mass and reduce the possibility of local collapses of rocks, thus the importance of the rock bolt should not be overlooked, regardless of the overall stability.

• Architectural research
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• 제20권4호
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• pp.129-135
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• 2018

In order to compare the development performance of headed reinforcing bar and straight reinforcing bar in tension for steel fiber reinforced concrete (SFRC), pullout test of specimens with reinforcing bar which was anchored on simple beam perpendicularly was conducted. The experimental variables were steel fiber volume ratio ($V_{Rsf}$), concrete compressive strength, and existence of head. As the result of test, splitting failure of concrete in the development direction of reinforcing bar in most specimens was observed. For development detail of headed reinforcing deformation bar, specimens with 1% $V_{Rsf}$ showed approximately 63%~119% increase in pullout strength compare to specimens with 0% $V_{Rsf}$. Test result shows that SFRC is more effective in increasing pullout strength for headed reinforcing bars than increasing pullout strength of straight bars.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.108-111
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• 2004

The polypropylene(PP) fiber is poised as a low cost alternative for reinforcement in structural applications in comparison with other high performance fibers, such as the polyvinyl-alcohol(PVA), polyethylene, carbon and aramid fiber. The mechanical properties of the composite are strongly determined by the interfacial behavior of fiber and cementitious matrix. The crack bridging mechanism contribute to composite toughness from activation of the fiber-matrix interface where energy is dissipated through debonding of the interface and fiber pullout. In this study, therefore, the pullout behavior of PP fibers is investigated. Experimental work includes the investigation of the interfacial properties, and the composite property. The quantification of interfacial properties, the frictional bond is achieved through single fiber pullout test. A study on the effect of inclination angle on fiber pullout behavior is also conducted.

• Geomechanics and Engineering
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• 제1권3호
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• pp.259-262
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• 2009

This paper examines the potential of relevance vector machine (RVM) in prediction of pullout capacity of small ground anchors. RVM is based on a Bayesian formulation of a linear model with an appropriate prior that results in a sparse representation. The results are compared with a widely used artificial neural network (ANN) model. Overall, the RVM showed good performance and is proven to be better than ANN model. It also estimates the prediction variance. The plausibility of RVM technique is shown by its superior performance in forecasting pullout capacity of small ground anchors providing exogenous knowledge.

• 한국지반공학회논문집
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• 제34권4호
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• pp.37-47
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• 2018

본 연구에서는 상대밀도와 세립분 함유율이 현장타설말뚝의 인발저항 성능에 미치는 영향을 평가하기 위하여, 다양한 상대밀도 및 세립분 함유율 조건에 대한 직접전단시험 및 모형말뚝 인발실험을 수행하였다. 직접전단시험으로부터 세립분 함유율에 따른 내부마찰각과 점착력의 변화특성을 정량적으로 파악할 수 있었으며, 인발실험 결과에서는 말뚝의 인발저항 성능에 미치는 상대밀도와 세립분 함유율의 영향을 확인할 수 있었다. 또한, 두 실험 결과를 비교 분석한 결과, 말뚝의 인발저항 성능에 대한 지반의 내부마찰각과 점착력의 기여도는 세립분 함유율 약 13%를 전후로 하여 서로 다르게 나타남을 알 수 있었다. 따라서 현장타설말뚝 설계 시 수행되는 마찰저항 성능 평가는 지반의 세립분 함유율에 따른 강도정수($c-{\phi}$)를 고려해야 할 것으로 평가되었다.

• International Journal of Concrete Structures and Materials
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• 제11권2호
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• pp.301-313
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• 2017

This paper presents the fibre-matrix interfacial properties of hooked end steel fibres embedded in ultra-high performance mortars with various water/binder (W/B) ratios. The principle objective was to improve bond behaviour in terms of bond strength by reducing the (W/B) ratio to a minimum. Results show that a decrease in W/B ratio has a significant effect on the bond-slip behaviour of both types of 3D fibres, especially when the W/B ratio was reduced from 0.25 to 0.15. Furthermore, the optimization in maximizing pullout load and total pullout work is found to be more prominent for the 3D fibres with a larger diameter than for fibres with a smaller diameter. On the contrary, increasing the embedded length of the 3D fibres did not result in an improvement on the maximum pullout load, but increase in the total pullout work.