• Structural Engineering and Mechanics
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• 제54권3호
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• pp.521-543
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• 2015

Depending on the damage type as well as the level of damage observed after the earthquake, certain measures should be taken for the damaged buildings. In this study, structural repairing of two different types of damaged RC beam-column assembly by carbon fiber-reinforced polymer sheets is investigated in detail as a member repairing technique. Two types of 1:1 scale test specimens, which represent the exterior RC beam-column connection taken from inflection points of the frame, are utilized. The first specimen is designed according to the current Turkish Earthquake Code, whereas the second one represents a deficient RC beam-column assembly. Both of the specimens were subjected to cyclic quasistatic loading in the laboratory and different levels of structural damage were observed. The first specimen displayed a ductile response with the damage concentrated in the beam. However, in the second specimen, the beam-column joint was severely damaged while the rest of the members did not attain their capacities. Depending on the damage type of the specimens, the damaged members were repaired by CFRP wrapping with different configurations. After testing the repaired specimens, it is found that former capacities of the damaged members were mostly recovered by the application of CFRPs on the damaged members.

• Steel and Composite Structures
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• 제48권5호
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• pp.599-610
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• 2023

To avoid debonding failure, a novel type of hybrid anchorage (HA) is proposed in this study that uses a slotted plate to lock the ends of the fiber-reinforced polymer (FRP) sheet in addition to the usual bonding over the substrate of the strengthened member. An experimental investigation was performed on three groups of RC beams, which differed from one another in either concrete strength or steel reinforcement ratio. The test results indicate that the end self-locking of the CFRP sheet can improve the failure ductility, ultimate capacity of the beams and its utilization ratio. Although intermediate debonding occurred in all the strengthened beams, it was not a fatal mode of failure for the three specimens with end anchorage. Among them, FRP rupture occurred in the beam with higher concrete strength and lower steel reinforcement ratio, whereas the other two failed by concrete crushing. The beam strengthened by HA obtained a relatively high percentage of increase in ultimate capacity when the rebar ratio or concrete strength decreased. The expressions in the literature were inspected to calculate the critical loads at intermediate debonding, FRP rupturing and concrete crushing after debonding for the strengthened beam. Then, the necessity of further research is addressed.

• 한국구조물진단유지관리공학회 논문집
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• 제17권1호
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• pp.37-45
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• 2013

본 연구에서는 다양한 RC 슬래브의 접촉 발파 실험을 수행하여 내폭 성능을 평가하였다. RC 슬래브의 내폭 성능 향상을 위해 섬유 보강과 외부 CFRP 시트 보강을 도입하였다. 폭발하중 실험은 $2,000{\times}1,000{\times}100mm$ RC 슬래브를 제작하였고, 일반 콘크리트와 강섬유 보강 콘크리트, 하이브리드 PVA 섬유 보강 시멘트 복합체, 초고성능 콘크리트를 적용하였다. 접촉 발파로 생긴 RC 슬래브의 손상 정도를 크레틀, 스폴과 브리치의 직경과 깊이로 평가하였다. 실험 결과를 LS-DYNA 유한요소해석 프로그램과 Morishita 등의 예측식으로 검증하고 비교분석하였다. 분석 결과, LS-DYNA 프로그램을 이용하여 크레틀, 스폴, 브리치의 직경 및 깊이에 대한 개략적인 예측이 가능하며, 폭발하중 하에서 손상부의 거시적 거동을 모사함으로써 부재의 파괴 이력을 나타낼 수 있었다. 국부 손상에 대한 세가지 예측식이 소개되어 있으나 경험식으로써의 한계가 존재하며, 이에 대한 추가 연구가 필요하다고 판단된다.

• 한국재난정보학회 논문집
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• 제12권1호
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• pp.54-61
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• 2016

구조물에 복합재료를 사용한 보강과 복구에 대한 사용이 증가하고 있는 상황에서 갑작스러운 강도저하로 발생되는 재난을 피하기 위하여 임시 보강하고자 탄소섬유 판을 이용하여 기존금속재와 접합(접착방식)을 통한 강도증진효과를 연구하였다. 특히 실험을 통하여 강-탄소섬유보강재로 이루어진 복합 재 거동을 파악하였으며 여기에 적절한 시험을 위한 새로운 형태의 시험편을 제작하였다. 접합재로 레진을 접착하는 부착 면을 달리하여 거동을 비교하기 위하여 표면처리가 다른 시험편을 각각 고려하여 시험한 결과 강성보강효과는 물론 일체거동의 특성이 잘 나타남을 알 수 있었다.

• Steel and Composite Structures
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• 제32권5호
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• pp.559-569
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• 2019

The bond strength between composite laminates and concrete is a key factor that controls the behavior of concrete members strengthened with fiber reinforced polymer (FRP) sheets, which can be affected by several parameters such as thermal stresses and surface preparation. This article presents the result of an experimental study on the bond strength between FRP sheets and concrete at ambient temperature after specimens had been exposed to elevated temperatures of up to $200^{\circ}C$. For this purpose, 30 specimens of plain concrete with dimensions of $150{\times}150{\times}350mm$ were prepared. Three different conventional surface preparation methods (sandblasting, wire brushing and hole drilling) were considered and compared with a new efficient method (fiber implantation). Deformation field during each experiment was monitored using particle image velocimetry. The results showed that, the specimens which were prepared by conventional surface preparation methods, preserved their bond integrity when exposed to temperature below glass transition temperature of epoxy resin (about $60^{\circ}C$). Beyond this temperature, the bond strength and stiffness decreased significantly (about 50%) in comparison with control specimens. However, the specimens prepared by the proposed method displayed higher bond strengths of up to 32% and 90% at $25^{\circ}C$ and $200^{\circ}C$, respectively.

• 콘크리트학회논문집
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• 제15권1호
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• pp.78-86
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• 2003

섬유보강재를 사용한 철근콘크리트 부재의 보강공법은 재료의 내부식성 및 시공의 편리성 등 여러 가지 장점으로 인하여 최근 그 사용이 현저하게 증가하고 있는 실정이다. 본 연구에서는 여러 가지 종류의 섬유보강재를 사용하여 휨보강된 철근콘크리트 보의 휨성능을 비교하고, 그 특성을 고려한 보강설계식을 제안하였다. 섬유보강재의 종류(아라미드, 유리, 탄소섬유) 및 보강비에 따른 철근콘크리트 보의 휨성능을 검토하기 위하여 3.2m 스팬의 단순보에 대한 실험을 실시하였으며, 실험의 결과를 최대내력, 강성 및 연성도의 관점에서 분석하였다. 본 연구의 실험결과, 부재의 휨보강내력은 보강재의 종류에 따른 인장강도보다는 강성에 주로 관계하는 것으로 나타났으며, 연성도는 강성이 증가할수록 감소하는 경향을 나타내었다. 본 연구에서는 이와 같은 실험결과를 기반으로 휨보강설계식을 제안하였으며, 이를 신뢰성있는 선행 연구자들의 연구결과와 비교하여 그 타당성을 검증하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.113-116
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• 2006

In this study, new bond-slip model is proposed. The proposed bond-slip model which has bilinear ascending regions and exponential descending region by modifying the conventional bilinear bond-slip model has been verified. Then, result by finite element analyses using interface element implemented with bond-slip model compared well with those of existing experiment researches on bond-slip models. It is shown that bond strength and effective bond length predicted by the bond-slip model and finite element analysis is good agreement with those of pull tests.

• Structural Engineering and Mechanics
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• 제25권6호
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• pp.675-690
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• 2007

In order to study the ductility and the lateral load carrying capacity of the masonry walls strengthened with CFRPs (Carbon Fiber Reinforced Polymer sheets), three pieces of masonry walls subjected to cyclic loads with low frequency and vertical load of constant amplitude have been tested. Two different strengthening methods have been used. The strengthening efficiency is affected by the strengthening method. A simplified calculation approach has been introduced based on the experimental test results, and the theoretical results agree reasonably well with the experimental results. It is found that the critical loads, the critical displacements, the ultimate loads, the ultimate displacements and the ductile coefficients of the masonry walls strengthened with CFRPs improve remarkably (6%~57%). Therefore, the masonry structures strengthened with CFRPs are of better ductility and of better lateral load carrying capacity than the masonry structures without any strengthening measurements.

• Advances in concrete construction
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• 제5권6호
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• pp.625-638
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• 2017

The flexural behavior of Fiber reinforced polymer (FRP) sheets has gained much research interest in the flexural strengthening of reinforced concrete beams. The study on flexure includes various parameters like increase in strength of the member due to the externally bonded (EB) Fiber reinforced polymer, crack patterns, debonding of the fiber from the structure, scaling, convenience of using the fibers, cost effectiveness, etc. The present work aims to study experimentally about the reasons behind the failure due to flexure of an externally bonded FRP concrete beam. In the design of FRP-reinforced concrete structures, deflection control is as critical as much as flexural strength. A numerical model is created using Finite element (FEM) software and the results are compared with that of the experiment.

• Composites Research
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• 제33권3호
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• pp.153-160
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• 2020

질화붕소(BN)는 높은 열전도도를 가지는 2D 형상의 부도체로 복합재료의 강화 필러로 연구되고 있는 물질이다. 본 연구에서는 판상의 육방정 질화붕소(h-BN)를 탄소섬유 다발 사이에 첨가하여 BN이 함유된 탄소섬유강화 복합소재(CFRPs)를 제조하여 BN 필러가 CFRP의 여러 물성에 어떤 영향을 주는지 탐구하였다. 사용된 프리프레그의 수지 총량의 0-15 wt%의 BN 필러가 프리프레그 층 사이에 첨가되었다. BN 필러가 첨가된 복합소재의 인장강도는 최대 13.6%, 계면간 전단응력은 최대 6.7% 증가하는 것을 관찰하였다. BN 첨가량에 따른 열전도도와 전기전도도의 변화와, BN의 첨가량에 따른 시편의 단면 형상 변화 또한 관찰되어 탄소섬유-BN-에폭시 복합소재의 물성 제어 가능성을 제시하였다.