• 전기전자학회논문지
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• 제20권4호
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• pp.424-427
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• 2016

이 논문에서는 FRP(Fiber Reinforced Polymer)의 내부 결함이나 물리적 손상을 검출하기 위하여 SAR(Synthetic Aperture Radar)를 이용한 마이크로파 비파괴 검사법(Microwave Nondestructive Inspecting)을 제안한다. 전파가 다층 유전체인 FRP에 수직으로 입사되면 계면이나 횡축 균열과 같은 결함에 좋은 반응을 나타낸다. 이때 반사파로부터 계면 깊이나 결함 위치를 SAR 이미지 기법으로 결함을 형상화할 수 있다. 그 결과, SAR 시스템으로 FRP 복합 소재 내부 결함들의 종류, 크기나 위치를 효율적으로 진단할 수 있음을 확인하였다.

• Advances in concrete construction
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• 제13권 2호
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• pp.183-190
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• 2022

A wide range of experimental bases and improved performance with different forms of Fiber Reinforced Polymer (FRP) have attracted researchers to produce eco-friendly and sustainable structures. The reinforced concrete (RC) beam's shear capacity has remained a complex phenomenon because of various parameters affecting. Design recommendations for the shear capacity of RC elements having FRP reinforcement need a more experimental database to improve design recommendations because almost all the recommendations replace different parameters with FRP's. Steel and FRP are fundamentally different materials. One is ductile and isotropic, whereas the other is brittle and orthotropic. This paper presents experimental results of the investigation on the beams with glass fiber reinforced polymer (GFRP) reinforcement as longitudinal bars and stirrups. Total twelve beams with GFRP reinforcement were prepared and tested. The cross-section of the beams was rectangular of size 230 × 300 mm, and the total length was 2000 mm with a span of 1800 mm. The beams are designed for simply-supported conditions with the two-point load as per specified load positions for different beams. Flexural reinforcement provided is for the balanced conditions as the beams were supposed to test for shear. Two main variables, such as shear span and spacing of stirrups, were incorporated. The beams were designed as per American Concrete Institute (ACI) ACI 440.1R-15. Relation of VExp./VPred. is derived with axial stiffness, span to depth ratio, and stirrups spacing, from which it is observed that current design provisions provide overestimation, particularly at lower stirrups spacing.

• Structural Engineering and Mechanics
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• 제72권2호
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• pp.155-168
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• 2019

This paper presents the results of an experimental investigation on the compressive strength of small scale concentrically axially loaded fiber-reinforced polymer (FRP) confined plain concrete columns, with cylinder concrete strength 19 MPa. For columns with circular (150-mm diameter) and square (150-mm side) cross sections wrapped with glass- and carbon-FRP sheets (GFRP and CFRP, respectively) applied with dry lay-up the effect of different jacket schemes and different overlap configurations on the confined characteristics is investigated. Test results indicate that the most cost effective jacket configuration among those tested is for one layer of CFRP, for both types of sections. In square sections the location of the lap length, either in the corner or along the side, does not seem to affect the confined performance. Furthermore, in circular sections, the presence of an extra wrap with FRP fibers parallel to the column's axis enhances the concrete strength proportionally to the axial rigidity of the FRP jacket. The recorded strains and the distributions of lateral confining pressures are discussed. Existing design equations are used to assess the lateral confining stresses and the confined concrete strength making use of the measured hoop strains.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.125-128
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• 2005

Recently new materials, such as fiber reinforced polymer(FRP) and other composite materials are being applied in reinforcing plate or plate or prestressing cables of concrete structures. Although these new materials themselves show the excellent durability and high strength, the bond behaviour between concrete surface and FRP is not well recognized. Therefore, this paper propose a evaluation method for effective bond length between fiber reinforced polymer(FRP) and concrete. To develop the evaluation method, this paper presents a review of current evaluation methods for effective bond length. These methods are compared by single face test, expose merits and demerits. And based on them, new evaluation method was developed. Finally, the new method was compared with existing methods to verify a adequateness for evaluation of effective bond length.

• 한국터널지하공간학회 논문집
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• 제12권6호
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• pp.451-461
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• 2010

장기 부식 등 일반적인 건설재료의 문제점을 보완할 수 있는 대체재료로서, 섬유강화 복합재료의 활용이 증대되고 있다. 하지만 일반적으로 선형의 섬유강화 복합재료를 아치형인 터널구조물의 부재로서 활용하는 데는 많은 문제점이 대두된다. 따라서, 본 연구에서는 섬유강화 복합부재를 일정곡률로 인발성형 할 수 있는 신개념의 곡면 FRP 부재 성형장비를 개발하고 시제품을 생산하였으며, 시제품에 대한 물리적 특성 시험을 수행하였다. 이어, 곡면 FRP 시제품과 합체되어 제작된 콘크리트 복합부재에 대한 수치해석 검토 및 분석을 통하여 시제품의 터널 구조체로써의 적용성을 평가하였다. 수치해석적 적용성 검토 결과, 곡면 FRP 부재를 터널 구조물로 적용함에 있어서 터널 안정성을 충분히 확보할 수 있는 것으로 파악되었다.

• Steel and Composite Structures
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• 제30권6호
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• pp.591-601
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• 2019

This research study investigates experimentally and analytically the axial compressive behaviour of Concrete Filled Fiber Reinforced Polymer Tube (CFFT) columns with and without Fiber Reinforced Polymer (FRP) bars. The experimental program comprises five circular columns of 204-206 mm outer diameter and 800-812 mm height. All columns were tested under concentric axial compressive loads. It was found that CFFT columns with and without FRP bars achieved higher peak axial compressive loads and corresponding axial deformations than conventional steel reinforced concrete (RC) column. The contribution of FRP bars was about 12.1% of the axial compressive loads carried by CFFT columns reinforced with FRP bars. Axial load-axial deformation ($P-{\delta}$) curves of CFFT columns were analytically constructed, which mapped well with the experimental $P-{\delta}$ curves. Also, an equation was proposed to predict the axial compressive load capacity of CFFT columns with and without FRP bars, which adequately considers the contributions of the circumferential confinement provided by FRP tubes and lower ultimate strength of FRP bars in compression than in tension.

• Steel and Composite Structures
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• 제38권2호
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• pp.165-176
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• 2021

Existing research on confined concrete filled steel tubular (CCFT) columns has been mainly focused on static or cyclic loading. In this paper, square section CCFT and CFT columns were tested under both static and impact loading, using a 10,000 kN capacity compression test machine and a drop weight testing equipment. Research parameters included bonded and unbonded fiber reinforced polymer (FRP) wraps, with carbon, basalt and glass FRPs (or CFRP, BFRP, and GFRP), respectively. Time history curves for impact force and steel strain observed are discussed in detail. Experimental results show that the failure modes of specimens under impact testing were characterized by local buckling of the steel tube and cracking at the corners, for both CCFT and CFT columns, similar to those under static loading. For both static and impact loading, the FRP wraps could improve the behavior and increase the loading capacity. To analyze the dynamic behavior of the composite columns, a finite element, FE, model was established in LS-DYNA. A simplified method that is compared favorably with test results is also proposed to predict the impact load capacity of square CCFT columns.

• 콘크리트학회논문집
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• 제23권5호
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• pp.675-682
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• 2011

최근 콘크리트 구조물의 보강시 사용되는 FRP(fiber reinforced polymer)를 이용한 보강에서, 철근콘크리트의 피복부분에 홈을 형성하고 이 홈내부에 FRP 바를 삽입한 후 에폭시 모르타르 등으로 보강하는 방법, 즉 표면매입보강(near-surface-mounted retrofit, NSMR)방법의 연구가 최근 활발히 진행되고 있다. 이 연구는 FRP 판을 철근콘크리트 표면에 매입보강시 FRP 판의 부착 특성을 실험적으로 연구한 논문이다. FRP 판의 매입 길이, 전단키의 유무, 보강열수 등을 변수로 부착 실험을 실시하여 파괴 기구를 관찰하고 이를 근거로 콘크리트 할렬 파괴시의 인발강도를 산정할 수 있는 강도식을 제안하였다. 실험 결과 매입 길이가 길수록 인발 내력은 증가하며 FRP 판의 열수가 증가할수록 내력이 증진되는 것으로 나타났다. 콘크리트의 할렬 파괴를 고려하여 내력을 산정한 결과 실험 결과와 좋은 대응을 보이는 것으로 나타났다.

• 콘크리트학회논문집
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• 제17권6호
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• pp.983-992
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• 2005

섬유에 의하여 보강된 철근콘크리트 보의 파괴모드는 섬유가 파단하여 전단강도에 도달하는 경우와 섬유가 파단하기 이전에 전단강도에 도달하는 경우로 나누어진다. 이와 같이 섬유가 파단강도에 도달하지 않는 경우에 두 파괴모드의 전단강도는 상이하다. 섬유가 파단하지 않고 전단강도에 도달할 경우에 보의 전단강도를 예측하기 위하여 섬유의 파단강도를 사용할 수 없으므로 기존의 제안식에서는 섬유강도저감계수를 사용하여 섬유보강 보의 전단강도를 예측하였다. 그러나 기존 제안식의 대부분은 실험결과에 근거한 회귀분석을 통하여 일정한 상수 값에 의하여 섬유강도저감계수를 평가하였으며, 섬유의 도달강도와 밀접한 관계가 있는 콘크리트의 압축강도를 고려하지 않고 있다. 이 연구에서는 변형률의 적합조건을 이용한 트러스모델에 근거하여 섬유보강 보의 파괴모드의 경계점을 구별하고, 이를 이용하여 섬유보강 보의 전단강도를 예측하였다.

• Structural Engineering and Mechanics
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• 제87권6호
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• pp.585-599
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• 2023

Geopolymer concrete (GC) can be competently utilized as a practical replacement for cement to prevent a high carbon footprint and to give a direction toward sustainable concrete construction. Moreover, previous studies mostly focused on the axial response of glass fiber reinforced polymer (glass-FRP) concrete compressive elements without determining the effectiveness of repairing them after their partial damage. The goal of this study is to assess the structural effectiveness of partially damaged GC columns that have been restored using carbon fiber reinforced polymer (carbon-FRP). Bars made of glass-FRP and helix made of glass-FRP are used to reinforce these columns. For comparative study, six of the twelve circular specimens-each measuring 300 mm×1200 mm-are reinforced with steel bars, while the other four are axially strengthened using glass-FRP bars (referred to as GSG columns). The broken columns are repaired and strengthened using carbon-FRP sheets after the specimens have been subjected to concentric and eccentric compression until a 30% loss in axial strength is attained in the post-peak phase. The study investigates the effects of various variables on important response metrics like axial strength, axial deflection, load-deflection response, stiffness index, strength index, ductility index, and damage response. These variables include concentric and eccentric compression, helix pitch, steel bars, carbon-FRP wrapping, and glass-FRP bars. Both before and after the quick repair process, these metrics are evaluated. The results of the investigation show that the axial strengths of the reconstructed SSG and GSG columns are, respectively, 15.3% and 20.9% higher than those of their original counterparts. In addition, compared to their SSG counterparts, the repaired GSG samples exhibit an improvement in average ductility indices of 2.92% and a drop in average stiffness indices of 3.2%.