• Title/Summary/Keyword: Fiber-reinforced polymer

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Ground Test & Evaluation of Conformal Load-bearing Antenna Structure for Communication and Navigation (통신 항법용 다중대역 안테나 내장 스킨구조의 지상시험평가)

  • Kim, Min-Sung;Park, Chan-Yik;Cho, Chang-Min;Jun, Seung-Moon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.41 no.11
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    • pp.891-899
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    • 2013
  • This paper suggests a test and evaluation procedure of conformal load-bearing antenna structure(CLAS) for high speed military jet application. A log periodic patch type antenna was designed for multi-band communication and navigation antenna. Carbon/Glass fiber reinforced polymer was used as a structure supporting aerodynamic loads and honeycomb layer was used to improve antenna performance. Multi-layers were stacked and cured in a hot temperature oven. Gain, VSWR and polarization pattern of CLAS were measured using anechoic chamber within 0.15~2.0 GHz frequency range. Tension, shear, fatigue and impact load test were performed to evaluate structural strength of CLAS. Antenna performance test after every structural strength test was conducted to check the effect of structural test to antenna performance. After the application of new test and evaluation procedure to validate a new CLAS, a design improvement was found.

Shape Optimum Design of Pultruded FRP Bridge Decks (인발성형된 FRP 바닥판의 형상 최적설계)

  • 조효남;최영민;김희성;김형열;이종순
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.17 no.3
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    • pp.319-332
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    • 2004
  • Due to their high strength to weight ratios and excellent durability, fiber reinforced polymer(FRP) is widely used in construction industries. In this paper, a shape optimum design of FRP bridge decks haying pultruded cellular cross-section is presented. In the problem formulation, an objective function is selected to minimize the volumes. The cross-sectional dimensions and material properties of the deck of FRP bridges are used as the design variables. On the other hand, deflection limits in the design code, material failure criteria, buckling load, minimum height, and stress are selected as the design constraints to enhance the structural performance of FRP decks. In order to efficiently treat the optimization process, the cross-sectional shape of bridge decks is assumed to be a tube shape. The optimization process utilizes an improved Genetic Algorithms incorporating indexing technique. For the structural analysis using a three-dimensional finite element, a commercial package(ABAQUS) is used. Using a computer program coded for this study, an example problem is solved and the results are presented with sensitivity analysis. The bridge consists of a deck width of 12.14m and is supported by five 40m long steel girders spaced at 2.5m. The bridge is designed to carry a standard DB-24 truck loading according to the Standard Specifications for Highway Bridges in Korea. Based on the optimum design, viable cross-sectional dimensions for FRP decks, suitable for pultrusion process are proposed.

Experimental Verification of Flexural Response for Strengthened R/C Beams by Stirrup Partial-Cutting Near Surface Mounted Using CFRP Plate (CFRP 플레이트 적용 스터럽 부분절단형 표면매립공법으로 보강된 철근콘크리트 보의 휨 거동에 대한 실험적 평가)

  • Oh, Hong-Seob;Sim, Jong-Sung;Ju, Min-Kwan;Lee, Gi-Hong
    • Journal of the Korea Concrete Institute
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    • v.20 no.6
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    • pp.671-679
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    • 2008
  • The near surface mounted (NSM) FRP strengthening method has been conventionally applied for strengthening the deteriorated concrete structures. The NSM strengthening method, however, has been issued with the problem of limitation of the cutting depth which is usually considered as concrete cover depth. This may be related with degradation of bonding performance in long-term service state. To improve the debonding problem, in this study, the Stirrup partial-cutting NSM (SCNSM) strengthening method using CFRP plate was newly developed. SCNSM strengthening method can be effectively applied to the deteriorated concrete structure without any troubles of insufficient cutting depth. To experimentally verify the structural behavior, the flexural test of the concrete beam by using the SCNSM strengthening method was conducted with the test variable as the strengthening length (32%, 48%, 70%, 80%, 96% of span length). In the result of the test, the NSM and SCNSM strengthened specimen showed similar structural behavior with load-deflection, mode of failure. Additionally, there was no apparent structural degradation by the stirrup partial-cutting. Consequently, it was evaluated that the SCNSM strengthening method can be useful for seriously damaged concrete structures that is hard to apply the conventional NSM strengthening method for increasing the structural capacity.

A Prediction of the Long-Term Deflection of RC Beams Externally Bonded with CFRP and GFRP (CFRP와 GFRP로 외부 부착된 철근콘크리트보의 장기 처짐 예측)

  • Kim, Sung-Hu;Kim, Kwang-Soo;Han, Kyoung-Bong;Song, Seul-Ki;Park, Sun-Kyu
    • Journal of the Korea Concrete Institute
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    • v.20 no.6
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    • pp.765-772
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    • 2008
  • For RC structures, long-term deformation occurs due to the inherent characteristics, which are creep and shrinkage. In terms of serviceability, it is important to limit deflection caused by the deformation to the allowable deflection. In the recent years, various repair and strengthening methods have been used to improve performance of the existing RC structures. One of the typical methods is FRP externally bonded method (EBR). Fiber reinforced polymer (FRP) has been used worldwide as repair and strengthening materials due to its superior properties. Besides, it has to offer improved strengthening performance not only under instantaneous load but sustained load. Therefore, accurate prediction method of deflection for the RC members externally bonded with FRP under sustained load is required. In this paper, three beams were fabricated. Two beams were externally strengthened with one of CFRP plate and GFRP plate respectively. Total three beams were superimposed under sustained load of 25 kN. During 470 days, deflections at midspan were obtained. Moreover, creep coefficients and shrinkage strains were calculated by using ACI-209 code and CEB-FIP code. In order to predict the deflection of the beams, EMM, AEMM, Branson's method and Mayer's method were used. Through the experiment, it was found that the specimen with CFRP plate has the most flexural capacity and Mayer's method is the most precise method to predict total long-term deflections.

Material Performance Evaluation of PolyUrea for Structural Seismic Retrofitting (구조물 내진 보강용 폴리우레아의 재료 성능 평가)

  • Cho, Chul-Min;Choi, Ji-Hun;Rhee, Seung-Hoon;Kim, Tae-Kyun;Kim, Jang-Ho Jay
    • Journal of the Korea Concrete Institute
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    • v.29 no.2
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    • pp.131-139
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    • 2017
  • Recently, earthquakes have frequently occurred near Korean peninsula. An experimental study is needed for developing a reinforcing method for seismic strengthening to apply to RC structures. Recently, PolyUrea (PU) as structural reinforcement materials has been receiving great interest from construction industry. The reinforcing effect of PU appeared to be excellent under blast and impact as well as earthquakes. In this study, Flexible Type PolyUrea (FTPU) developed in preceding studies was modified to develop Stiff Type PolyUrea (STPU) by varying the ratio of the components of prepolymer and hardener of FTPU. The material performance evaluation has been performed through hardening time, tensile strength and percent elongation test, pull-off test, and shore hardness test. The experimental results showed that STPU has higher tensile strength and lower elongation than FTPU. Therefore, STPU coating agent can be used for semi-permanent products. By using STPU with Fiber-Reinforced Polymer (FRP) on concrete columns, confinement effect can be enhanced to maximize seismic strength and ductility.

Feasibility of Bladder Compression Molded Prepreg as Small Wind Turbine Blade Material (소형 풍력 터빈 블레이드 재료로서 블래더 가압 방식 몰드 성형 프리프레그의 타당성)

  • Yi, Bo-Gun;Seo, Seong-Won;Song, Myung-Ho
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.33 no.2
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    • pp.95-101
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    • 2020
  • The wind turbine blades should be designed to possess a high stiffness and should be fabricated with a light and high strength material because they serve under extreme combination of lift and drag forces, converting kinetic energy of wind into shaft work. The goal of this study is to understand the basic knowledge required to curtail the process time consumed during the construction of small wind turbine blades using carbon fiber reinforced polymer (CFRP) prepeg composites. The configuration of turbine rotor was determined using the QBlade freeware program. The fluid dynamics module simulated the loads exerted by the wind of a specific speed, and the stress analysis module predicted the distributions of equivalent von Mises stress for representing the blade structures. It was suggested to modify the shape of test specimen from ASTM D638 to decrease the variance in measured tensile strengths. Then, a series of experiments were performed to confirm that the bladder compression molded CFRP prepreg can provide sufficient strength to small wind turbine blades and decrease the cure time simultaneously.

An Experimental Study for Flexure/Shear Failure Behavior of Composite Beam with GFRP Plank Used As a Permanent Formwork and Cast-in-place High Strength Concrete (영구거푸집으로 사용한 유리섬유 FRP 판과 현장타설 고강도콘크리트로 이루어진 합성보의 휨/전단파괴거동에 관한 실험적 연구)

  • Yoo, Seung-Woon
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.16 no.6
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    • pp.4245-4252
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    • 2015
  • In this study, an experiment which utilized glass fiber reinforced polymer(GFRP) plank as the permanent formwork of cast-in-place high strength concrete structures was performed. The GFRP plank currently being produced has smooth surface so that it causes problems in behavior with concrete. Therefore, this research analyzed the flexure/shear failure behavior of composite beams, which used GFRP plank as its permanent formwork and has short shear span ratio, by setting the sand coated at GFRP bottom surface, the perforation and interval of the GFRP plank web, and the width of the top flange as the experimental variables. As a result of the experiments for effectiveness of sand attachment in case of not perforated web, approximately 47% higher ultimate load value was obtained when the sand was coated than not coated case and bending/shear failure mode was observed. For effectiveness of perforation and interval of gap, approximately 24% higher maximum load value was seen when interval of the perforation gap was short and the fine aggregate was not coated, and approximately 25% lower value was observed when the perforation gap was not dense on the coated specimen. For effectiveness of top flange breadth, the ultimate load value was approximately 17% higher in case of 40mm than 20mm width.

A Fundamental Study on the Load Resistance Characteristics of Revetment Concrete Block with Recycled Concrete Aggregate and GFRP Rebar (순환골재와 GFRP 보강근을 적용한 호안블럭의 하중저항특성에 관한 연구)

  • Kim, Yongjae;Kim, Jongho;Moon, Doyoung
    • Resources Recycling
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    • v.31 no.5
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    • pp.42-51
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    • 2022
  • Aggregate resources in Korea are expected to run out owing to an increase in development demand and construction investment. Recycled concrete aggregates (RCA), extracted from waste concrete, have a lower quality than natural aggregates. However, RCA can produce concrete similar in quality to the normal concrete by aggregate pretreatment, use of admixtures, and quality control. RCA are most suitable for use in precast concrete products such as sidewalk blocks and revetment blocks. Herein, the feasibility of producing revetment blocks using recycled aggregate concrete (RAC), similar in quality to normal concrete, was analyzed. The amount of RCA was varied, and moderate high early strength cement and steam curing were used to produce the concrete test blocks. In the block test, the load resistance characteristics of the blocks were evaluated to determine optimal RAC and glass fiber reinforced polymer (GFRP) rebar compositions. Thus, the variable that reduced the cement content was determined at the same level as that of natural aggregate concrete by the control of steam curing. In the concrete block test, although this depends on the reinforcement ratio, the RAC block exhibited the same or better performance than a normal concrete block. Therefore, the low quality of RCA in RAC is no longer a problem when concrete mixing and curing are controlled and appropriate reinforcement is used.

Experimental Study on Flexural Behavior of RC Beams Strengthened with Prestressed CFRP Plate (CFRP판으로 프리스트레싱 보강한 RC 보의 휨거동에 관한 실험적 연구)

  • Han, Sang-Hoon;Hong, Ki-Nam;Kim, Hyung-Jin;Woo, Sang-Kyun
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.2A
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    • pp.301-310
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    • 2006
  • Carbon fiber reinforced polymer (CRFP) materials are well suited to the rehabilitation of civil engineering structures due to their corrosion resistance, high strength to weight ratio and high stiffness to weight ratio. Their application in the field of the rehabilitation of concrete structures is increased due to the vast number of bridges and buildings in need of strengthening. However, RC members, strengthened with externally bonded CFRP plates, happened to collapse before reaching the expected design failure load. Therefore, it is necessary to develop the new strengthening method to overcome the problems of previous bonded strengthening method. This problems can be solved by prestressing the CFRP plate before bonding to the concrete. In this study, a total of 21 specimens of 3.3 m length were tested by the four point bending method after strengthening them with externally bonded CFRP plates. The CFRP plates were bonded without prestress and with various prestress levels ranging from 0.4% to 0.8% of CFRP plate strain. All specimen with end anchorage failed by a plate fracture regardless of the prestress levels while the specimen without end anchorage failed by the separation of the plate from the beam due to premature debonding. The cracking loads was proportionally related to the prestress levels, but the maximum loads of specimens strengthened with prestressed CFRP plates were insignificantly affected by the prestress levels.

Strength and Deformation Capacities of Short Concrete Columns with Circular Section Confined by GFRP (GFRP로 구속된 원형단면 콘크리트 단주의 강도 및 변형 능력)

  • Cho, Soon-Ho
    • Journal of the Korea Concrete Institute
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    • v.19 no.1
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    • pp.121-130
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    • 2007
  • To investigate the enhancement in strength and deformation capacities of concrete confined by FRP composites, tests under axial loads were carried out on three groups of thirty six short columns in circular section with diverse GFRP confining reinforcement. The major test variables considered include fiber content or orientation, wrap or tube type by varying the end loading condition, and continuous or discontinuous confinement depending on the presence of vortical spices between its two halves. The circumferential FRP strains at failure for different types of confinements were also investigated with emphasis. Various analytical models capable of predicting the ultimate strength and strain of the confined concrete were examined by comparing to observed results. Tests results showed that FRP wraps or tubes provide the substantial increase in strength and deformation, while partial wraps comprising the vertical discontinuities fail in an explosive manner with less increase in strength, particularly in deformation. A bilinear stress-strain response was observed throughout all tests with some variations of strain hardening. The failure hoop strains measured on the FRP surface were less than those obtained from the tensile coupons in all tests with a high degree of variation. In overall, existing predictive equations overestimated ultimate strengths and strains observed in present tests, with a much larger scatter related to the latter. For more accuracy, two simple design- oriented equations correlated with present tests are proposed. The strength equation was derived using the Mohr-Coulomb failure criterion, whereas the strain equation was based on entirely fitting of test data including the unconfined concrete strength as one of governing factors.