• Journal of the Korean Society for Advanced Composite Structures
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• v.4 no.3
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• pp.1-6
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• 2013

In this study, a shape of connector on seismic reinforced strip, which did not cause any physical damage to concrete column and can repair and reinforcement was decided by using nonlinear finite element analysis. Load displacement was applied on the concrete attached by strip. Stress distribution of connector by extension of concrete were checked. Through stress distribution of this analysis results, the most favorable shape was selected as a shape of the connector.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.124-133
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• 2007

In our research, we focused on the FBG sensor system which is one of the fiber optic sensor system. The FBG sensor system is used for structural measurements. The problem of FBG sensor is very thin and weak. The methods that can protect FBG optical fiber sensor front outside forces such as the impacts are investigated. The FBG sensor embedded in the fiber reinforced composites which can replace the reinforcing steel bars in concretes can be applied to the concrete structures by embedding to the composite materials. The progresses in tensile strength of FBG sensor embedded in the reinforcing FRP bars in the concrete structures compare to plain FBGs were observed and the good long term durability is expected.

• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2012.03a
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• pp.75-75
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• 2012

탄소섬유는 전구체의 종류에 따라 PAN계, 피치계 그리고 레이온계로 나뉘며 최종 탄소섬유의 특성에도 차이가 있는 것으로 알려져 있다. 최근에는 PAN계 탄소섬유가 세계 시장의 대부분을 차지하고 있으며, PAN계 탄소섬유의 초경량, 고강도, 고탄성, 내약품성 그리고 열안정성 등의 우수한 특성으로 최첨단 고기능성 제품의 복합재로 많이 이용되고 있다. 그러나 탄소섬유가 가지고 있는 높은 열전도성은 적용에 따라 단점으로 작용될 수도 있다. 예를 들면, 로켓 엔진의 노즐이나 원자로의 구조물 그리고 극한조건용 구조재료 등, 고강도 단열특성을 요하는 최첨단 복합재로 응용 범위를 넓히는데 한계로 작용한다. 레이온은 최초의 탄소섬유 전구체였으나 공정상 경제성이 떨어지는 이유로, 지금은 고탄성을 요구하는 특수 목적으로만 소량 생산되고 있다. 레이온의 주원료는 셀룰로오스이며 셀룰로오스는 지구상에서 가장 흔한 재료이므로 오늘날 셀룰로오스를 보강재로 이용하려는 연구가 활발히 진행되고 있다. 본 연구에서는 탄소섬유의 열전도도를 낮추기 위한 방법으로 안정화셀룰로오스를 첨가한 PAN용액을 출발물질로 탄소섬유를 제조하고 특성 연구를 진행하였다. PAN용액에 셀룰로오스의 분산성을 향상시키기 위해 셀룰로오스를 열처리하였다. 이 과정에서 얻어진 안정화 셀룰로오스의 수율을 높이기 위해 셀룰로오스를 난연 처리하였으며, 그 결과 안정화셀룰로오스의 수율을 향상시킬 수 있었다. 안정화셀룰로오스를 첨가시킨 PAN계 탄소섬유의 물리적, 기계적 그리고 열적 특성을 SEM, XRD, 만능 인장시험기, TGA 그리고 Laser Flash Method 등을 통해 주요 특성 및 변화를 관찰한 결과, 순수한 PAN계 탄소섬유의 특성과 유사한 결과를 얻었다. 향후 몇 가지 공정상의 문제점을 개선한다면 흥미로운 결과를 기대할 수 있을 것으로 본다.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.245-246
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• 2010

The purpose of this research is to investigate the nonlinear shear characteristics of Glass Fiber Reinforced Polymer(GFRP). FRP shear tests are conducted to determine the nonlinear shear behavior in accordance with ASTM specifications. The results obtained by these tests provides the exact shear properties and finally will be used to predict the long-term performance of RC structures applied by shear force.

• Composites Research
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• v.16 no.3
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• pp.32-40
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• 2003

In recent years, the investigation on the development of fiber reinforced plastic(FRP) Re-Bar has been greatly increased due to the attractive physical and mechanical properties of FRP. The primary reason of such a tendency is in the fact that it does not ordinarily cause durability problems such as those associated with steel reinforcement corrosion. This study is an experimental investigation on the flexural behavior of one-way concrete slabs, which can be used to construct bridge deck, reinforced with GFRP Re-Bar bundle. The tensile tests of GFRP Re-Bar produced by domestic industry and third point bending tests of one-way slab specimens reinforced with GFRP Re-Bar bundle are peformed. For all slab specimens, load-deflection relations are predicted by using the ACI committee 440 and the results are compared with experimental ones. In order to establish the design criteria or guidelines of concrete flexural member reinforced with FRP Re-Bar, it is needed to evaluate the serviceability limit state as well as the strength limit state.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.11
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• pp.19-26
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• 2018

This paper presents the shear strengthening effect of externally post-tensioning (EPT) method using high-strength steel rod in pre-cracked reinforced concrete (RC) beams. Three- and four-point bending tests were performed on a total of 8 specimens by adjusting the strengthening depths in the deviator position of EPT. The effective strengthening depths were 435, 535, and 610 mm. The pre-loading up to about 2/3 of ultimate load capacity measured in unstrengthened RC beam were applied in the beam to be post-tensioned. The EPT method was then applied to the pre-damaged RC beams and re-loading was added until the end of the test. EPT restored deflections of 3 mm or more, which account for about 40% of deflection when the pre-loading was applied. The shear strengthening increases more than 3 times and 36~107% in terms of the stiffness and load-carrying capacity compared to unstrengthening RC beams. The increased load-carrying capacities of the post-tensioned beam with strengthening depths of 435 and 535 mm are almost the same as 36~61%, and those of 610 mm are 84~107%, which shows the greatest shear strengthening effect.

• Journal of the Korea Concrete Institute
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• v.21 no.3
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• pp.303-310
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• 2009

CFRP(carbon fiber reinforced polymer) tendons can be used as an alternative to solve the corrosion problem of steel tendons. Material properties of CFRP tendons such as bond strength, transfer length, and development length should be determined in order to apply to concrete structures. First of all, in case of application for pretension concrete members with CFRP tendons, transfer length is an important factor. A total of 9 beams have been cast to determine transfer length and development length of domestic CFRP tendon in this paper. Test results revealed that transfer length of the prestressing 25% and 50% are 34D, 55D respectively. Also, transfer length has increased as the prestressing force has increased. A change was observed in transfer length of developed CFRP tendon after 9 weeks. ${\alpha}_t$ of developed CFRP tendon was 2.3 similar to the steel strand.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.3
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• pp.125-132
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• 2014

Steel fiber is a effective composite for crack resistance and improve structural performance under tensile loading. This study presents an evaluation of crack resistance and structural performance in cement mortar with steel fiber and expansion agent through internal chemical prestressing. For this work, cement mortar samples with 10% replacement of cement binder with CSA (Calcium-Sulfo-Aluminate) expansion agent and 1% volume ratio of steel fiber are prepared. Including basic mechanical properties, initial cracking load and fracture energy are evaluated in cement mortar beam with notch. Initial cracking load and fracture energy in cement mortar with CSA and steel fiber increase by 1.75 and 1.41~1.53 times compared with those in cement mortar with steel fiber. With optimum mix design for steel fiber and CSA expansive agent, the composite with chemical prestressing can be applied to various members and effectively improve crack resistance to external loading.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.54-63
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• 2022

This paper is a study on the friction damper, which is one of the seismic reinforcement devices for structures. This study developed a damper by replacing the internal friction material with ultra high molecular weight polyethylene (UHMWPE), a type of composite material. In addition, this study applied a multi-friction method in which the internal structure where frictional force is generated is laminated in several layers. To verify the performance of the developed multi-friction damper, this study performed a characteristic analysis test for the basic physical properties, wear characteristics, and disc springs of the material. As a result of the wear test, the mass reduction rate of UHMWPE was 0.003%, which showed the best performance among the friction materials based on composite materials. Regarding the disc spring, this study secured the design basic data from the finite element analysis and experimental test results. Moreover, to confirm the quality stability of the developed multi-friction damper, this study performed an seismic load test on the damping device and the friction force change according to the torque value. The quality performance test result showed a linear frictional force change according to the torque value adjustment. As a result of the seismic load test, the allowable error of the friction damper was less than 15%, which is the standard required by the design standards, so it satisfies the requirements for seismic reinforcement devices.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.222-229
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• 2022

The extensive use of external prestressing system with PSC-I beam to strengthen reinforced and prestressed concrete members requires the full understanding of the behavior of the strengthened members. The main approach of this research was to experimentally investigate the flexural performance of the PSC-I beam considering external tendon and an equation was developed which indicated the produced incremental stress in the tendon due to applied load. Further, this equation was verified through performing static loading tests on two experimental specimens considering the presence or absence of external tendon. The test results revealed that, the flexural performance enhanced due to the use of external tendon. Moreover, the magnitude of the estimated flexural strength using proposed stress increasing equation almost coincides with the experimental test results. However, it was the evident of the improvement of the flexural performance of the system by reinforcing with the external tendon and also proved that the proposed equation was valid and effective.