• 한국구조물진단유지관리공학회 논문집
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• 제24권6호
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• pp.153-160
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• 2020

지진동 하의 구조 시스템에서 기둥은 가장 중요한 구조 요소 중 하나이다. 이러한 관계로, 철근콘크리트(RC) 기둥의 내진 성능에 FRP 보강이 미치는 영행을 평가하기 위하여 광범위한 실험 연구가 이루어졌다. 이 중 상당수는 CFRP 또는 GFRP로 보강된 원형 단면 또는 정사각형 단면의 RC 기둥의 지진 거동에 집중하였다. 단면의 형태가 FRP 보강으로 인한 구속 효과에 영향을 미치기 때문에, 보강 효과와 최종 파괴 패턴이 형상에 따라 상이할 수 있다. 본 연구에서는 현무암 섬유를 함유한 BFRP 시트와 복합섬유 패널로 보강한 직사각형 단면을 가진 RC 기둥의 지진 거동을 살펴보기 위하여 반복하중 실험을 수행하였다. 실험 결과는 보강 효과가 크지 않았음을 보여주는데, BFRP 시트와 복합섬유 패널에 의한 구속 효과의 증가가 미미했음을 의미하며, 이는 기둥 단면 형상에 일부 기인하는 것으로 판단된다.

• 콘크리트학회논문집
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• 제23권1호
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• pp.31-38
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• 2011

이 연구에서는 FRP와 강섬유로 보강한 콘크리트 시편의 충격하중과 정적하중에서의 거동을 보기 위해 휨 실험과 펀칭 실험을 수행하였다. 1방향 휨 실험과 2방향 펀칭 실험에서 콘크리트 시편은 각각 $50{\times}100{\times}350$ mm와 $50{\times}350{\times}350$ mm의 크기로 제작하였다. 0.75% 혼입률의 강섬유 보강 콘크리트는 2방향 충격하중 및 정적하중에서 높은 저항 성능을 보였다. 일반 콘크리트와 강섬유 보강 콘크리트에서 FRP 보강은 높은 성능 증가를 보였다. 초고성능 콘크리트는 콘크리트 자체가 가지고 있는 높은 인장강도와 인성으로 인해, CFRP로 보강한 경우 강도와 에너지 소산 능력이 크게 증가하지 않았다.

• Structural Engineering and Mechanics
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• 제90권1호
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• pp.71-81
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• 2024

Fiber Reinforced Polymer (FRP) bars have now been widely adopted as an alternative to traditional steel reinforcements in infrastructure and civil industries worldwide due variety of merits. This paper presents a numerical methodology to investigate FRP bar-reinforced beam-column joint behavior under quasi-static loading. The proposed numerical model is validated with test results considering load-deflection behavior, damage pattern at beam-column joint, and strain variation in reinforcements, wherein the results are in agreement. The numerical model is subsequently employed for parametric investigation to enhance the end-span beam-column joint performance using different joint reinforcement systems. To reduce the manufacturing issue of bend in the FRP bar, the headed FRP bar is employed in a beam-column joint, and performance was investigated at different column axial loads. Headed bar-reinforced beam-column joints show better performance as compared to beam-column joints having an L-bar in terms of concrete damage, load-carrying capacity, and joint shear strength. The applicability and efficiency of FRP bars at different story heights have also been investigated with varying column axial loads.

• 콘크리트학회논문집
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• 제16권4호
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• pp.565-572
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• 2004

The mechanical behavior of concrete-filled glass fiber reinforced polymer columns is affected by various factors including concrete strength, stiffness of tube, end confinement effect, and slenderness ratio of members. In this research the behavior of slender columns was examined both experimentally and analytically. Experimental works include 1) compression test with 30cm long glass fiber composite columns under different end confinement conditions, 2) uni-axial compression test for 7 slender columns, which have various slenderness ratios. Short-length stocky columns gave high strength and ductility revealing high confinement action of FRP tubes. The strength increment and strain change were examined under different end confinement conditions. With slender columns, failure strengths, confinement effects, and stress-strains relations were examined. Through analytical work, effective length was computed and it was compared with the amount of reduction in column strength, which is required to predict design strength with slender specimens. This study shows the feasibility of slender concrete-filled glass fiber reinforced polymer composite columns.

• Structural Engineering and Mechanics
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• 제37권1호
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• pp.95-110
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• 2011

This paper presents a tri-uniform bond stress model for predicting the lap splice strength of reinforcing bar at the critical bond splitting failure. The proposed bond distribution model consists of three zones, namely, splitting zone, post-splitting zone and yielding zone. In each zone, the bond stress is assumed to be constant. The models for bond strength in each zone are adopted from previous studies. Combining the equilibrium, strain-slip relation and the bond strength model in each zone, the steel stress-slip model can be derived, which can be used in the nonlinear frame analysis of the column. The proposed model is applied to derive explicit equations for predicting the strength of the lap splice strengthened by fiber reinforced polymer (FRP) in both elastic and post-yield ranges. For design purpose, a procedure to calculate the required FRP thickness and the number of FRP sheets is also presented. A parametric investigation was conducted to study the relation between lap splice strength and lap splice length, number and thickness of FRP sheets and the ratio of concrete cover to bar diameter. The study shows that the lap splice strength can be enhanced by increasing one of these parameters: lap splice length, number or thickness of FRP sheets and concrete cover to bar diameter ratio. Verification of the model has been conducted using experimental data available in literature.

• Advances in concrete construction
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• 제10권2호
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• pp.93-104
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• 2020

Basalt fiber is an eco-friendly fiber and comparatively newer to the world of fiber-reinforced polymer (FRP) composites. A limited number of studies have been reported in the literature on the strengthening of reinforced concrete (RC) beams with basalt fiber reinforced polymer (BFRP). The present experimental work explores the feasibility of using the BFRP strips for shear strengthening of the RC beams. The strengthening schemes include full wrap and U-wrap. A simple mechanical anchorage scheme has been introduced to prevent the debonding of U-wrap as well as to utilize the full capacity of the BFRP composite. The effect of varying shear span-to-effective depth (a/d) ratio on the behavior of shear deficient RC beams strengthened with BFRP strips under different schemes is examined. The RC beams were tested under a four-point loading system. The study finds that the beams strengthened with and without BFRP strips fails in shear for a/d ratio 2.5 and the enhancement of the shear capacity of strengthened beams ranges from 5% to 20%. However, the strengthened beams fail in flexure, and the control beam fails in shear for a higher a/d ratio, i.e., 3.5. The experimental results of the present study have been compared with the analytical study and found that the latter gives conservative results.

• 한국구조물진단유지관리공학회 논문집
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• 제19권1호
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• pp.45-52
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• 2015

섬유복합체 (Fiber Reinforced Polymer, FRP)는 비강도가 높고, 비부식성 재료라는 특징을 가지고 있어서 건설 분야에서 철근을 대체할 수 있는 보강근 재료로 인식되고 있다. 몇몇 유리섬유 복합체 (Glass FRP, GFRP) 보강근이 상용화되어 있지만 GFRP는 철근에 비해 가격이 비싸고 상대적으로 낮은 탄성계수와 취성 파괴 특성 때문에 다소 경쟁력이 떨어진다. GFRP 보강근의 재료가격을 낮출 수 없다면 사용된 재료의 성능을 최대로 하여 보강근의 성능을 높이는 것이 상대적인 가격을 낮추는 방법이 될 수 있다. 일반적으로 FRP 보강근의 직경이 커질수록 인장강도는 감소하는 것으로 알려져 있다. 이의 원인 중 하나는 보강근이 인장을 받을 때 외력이 중앙에 위치한 섬유에 충분히 전달되지 못하여 외측에 위한 섬유들만이 인장에 저항하기 때문이다. 따라서 본연의 역할을 수행하지 못하는 섬유는 제거함으로써 보강근의 단가를 낮추면서 보강근이 소정의 성능을 발휘하도록 한다면 가격대비 성능이 최적화된 FRP 보강근을 제작할 수 있다. 본 연구에서는 직경 19 mm의 GFRP 보강근에 대해 단면 내에 중공이 존재하는 경우 중공비율에 따른 인장특성의 변화를 실험적으로 관찰하였다. 중공이 없는 GFRP 보강근 세 개, 네 가지 중공비율에 대해 각각 여섯 개의 GFRP 보강근 시편을 준비하여 인장실험을 실시하였으며 결과 분석을 통하여 인장특성 변화를 도출하였으며 이를 바탕으로 최적의 중공비율을 제안하였다.

• Ocean Systems Engineering
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• 제8권4호
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• pp.409-426
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• 2018

This paper presents the strengthening of tubular joint by wrapping Carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP). In this study, total number of layers, stacking sequence and length of wrapping are the different parameters involved when fiber reinforced polymers (FRP) composites are used for strengthening. For this, parameters where varied and results were compared with the reference joint. The best stacking sequence was identified which has the highest value in ultimate load with lesser deflections. For determining the best stacking sequence, numerical investigation was performed on CFRP composites; length of wrapping and number of layers were fixed. Later, the studies were focused on CFRP and GFRP strengthened joint by varying the total number of layers and length of wrapping. An attempt was done to propose a parametric equation from multiple regression analysis, which can be used for CFRP strengthened joints. Hashin failure criteria was used to check the failure of composites. Results revealed that FRP was having a greater influence in the load bearing capacity of joints, and in reducing the deflections and stresses of joint under axial compressive loads. It was also seen that, CFRP was far better than GFRP in reducing the stresses and deflection.

• Steel and Composite Structures
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• 제11권4호
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• pp.325-340
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• 2011

Based on the experimental data presented in part I of these companion papers, a semi-empirical model is proposed for axial stress-strain curves of reinforced high-strength concrete square columns confined by aramid fiber reinforced polymer (FRP) jackets. Additionally, a three-dimensional finite element model is developed to simulate the mechanical behaviors of the columns. In the finite element model, both material nonlinear and contact nonlinear are taken into account. Moreover, the influence of contact nonlinear (i.e., the end friction on the contact surface between test machines and specimens) is investigated deeply. Predictions from both the semi-empirical model and the finite element model agree with the experimental results, and it is also demonstrated that the friction coefficient of end friction notably affect the properties of columns when it ranges from 0.00 to 0.25.

• 한국터널지하공간학회 논문집
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• 제13권2호
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• pp.149-158
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• 2011

최근 장기 부식 등 일반적인 건설재료의 문제점을 보완할 수 있는 대체 재료로서, 섬유강화 복합재료의 활용이 증대되고 있다. 하지만 일반적으로 선형의 섬유강화 복합재료를 아치형인 터널구조물의 부재로서 활용하는 데는 많은 문제점이 대두된다. 본 연구에서는 FRP 복합부재의 거동특성 파악을 위한 수치해석적 사전검토 연구를 토대로, 터널 지보구조물로서 활용성 분석을 위한 FRP와 콘크리트 합성부재에 대한 하중재하 실험을 수행하였다. 또한 역학적 거동분석을 위하여 동일 조건에 대한 수치해석을 수행하였다. 하중재하 실험 및 수치해석결과, FRP와 콘크리트 합성부재는 두 부재 계면의 휨 인장에 의한 전단거동에 큰 영향을 받는 것으로 나타났다.