고성능 셀룰로우스 섬유보강 시멘트 복합체의 수분영향에 관한 연구

원종필,문제길 한국콘크리트학회 1996 콘크리트학회지 Vol.8 No.5

셀룰로우스 섬유는 강도와 강성측면에서 우수하고 동시에 적은 에너지로 가공이 가능하며, 또한 가격 면에서도 유리하고 풍부한 양으로 인해 시멘트의 보강재료로서 적당하다. 셀룰로우스 섬유 시멘트 복합체는 일반적으로 슬러리-탈수 가공에 의해 생산되며 평면이나 곡면 등의 시멘트 복합제품으로 얇은 판을 만드는데 주로 사용되어진다. 본 연구에서는 셀룰로우스 섬유 혼입률과 여러 가지 수분상태에서의 강도 특성을 실험에 의해 고찰하였다. 이들 시멘트 복합체의 강도효과에 대한 실험결과들의 검증을 위하여 통계학적인 분산분석과 다중비교에 의한 분석을 수행하였다. 휨강도는 섬유 혼입률이 약 8%까지 상승할 때 증가하였으며, 휨인성은 섬유 혼입률의 증가에 따라 증가하였다. 수분함유량은 휨강도에 중요한 요인으로 작용하였는데, 수분 함유량의 증가는 휨강도의 감소를 가져온 반면, 휨인성의 증가를 보여주었다. 시멘트 복합체에 포졸란 재료를 사용하였을 경우 수분에 의한 영향은 크지 않은 것으로 나타났으며 약간의 휨인성의 감소와 더불어 휨강도의 증가를 보였다. Cellulose fibers, being fairly strong and stiff as well as cheap and plentiful with low energy demand during manufacture, are strong contenders for the reinforcement of cement-based materials. Cellulose fiber-cement composites, generally manufactured by slurry-dewatering procedure, can find applications in the production of flat and corrugated cement sheets and many other thin-sheet cement products. This paper presents the results of an experimental study concerned with the effects of fiber content and moisture conditions on the flexural performance of these composites. An effort was also made to study the effect of pozzolanic admixtures on the flexural performance in different moisture conditions. The test results obtained were analyzed statistically using the analysis of variance in order to derive reliable conclusions. The results generated in this study were indicative of significant effects of fiber content and moisture condition of flexural performance. There is a tendency in flexural strength to increase in increase in fiber content up to 8%: flexural toughness values continue to increase even at higher fiber contents. Moisture content has a significant effect on the flexural performance. There is a tendency in flexural strength to decrease and flexural toughness to increase with increasing moisture content Composites incorporating pozzolans showed an increase in the flexural strength while slightly reducing the flexural toughness and were sensitive to variations in moisture content.

속채움 콘크리트 및 길이방향 철근으로 보강된 PHC 파일의 휨성능

한선진 ( Sun-jin Han ),이정민 ( Jungmin Lee ),김민석 ( Min-seok Kim ),김재현 ( Jae-hyun Kim ),김강수 ( Kang Su Kim ),오영훈 ( Young-hun Oh ) 한국구조물진단유지관리공학회 2021 한국구조물진단유지관리공학회 논문집 Vol.25 No.3

이 연구에서는 속채움 콘크리트와 길이방향 철근으로 보강된 PHC 파일에 대한 휨실험을 수행하였으며, 실험의 주요 변수는 길이 방향 철근비와 PHC 파일 중공 내부 표면에 형성된 슬러지 유무로 설정하였다. 총 6개의 PHC 파일 실험체를 제작하였으며, 실험체들의 파괴모드, 균열패턴, 단면내 길이방향 변형률 분포, PHC 파일과 속채움 콘크리트 사이에 발생된 단부 슬립을 상세히 계측하고 분석하였다. 실험결과, 길이방향 철근비가 증가할수록 휨 강성 및 강도가 증가하는 것으로 나타났으며, PHC 파일 내부 표면에 형성된 슬러지는 실험체의 휨성능에 큰 영향을 미치지 않는 것으로 나타났다. 실험적 연구와 더불어 이 연구에서는 변형률 적합조건, PHC 파일과 속채움 콘크리트 단면내 변형률 및 응력 분포를 고려한 비선형 휨해석 모델을 제안하였으며, 해석결과를 실험결과와 비교하여 제안모델의 합리성을 검증하였다. 그 결과, 제안모델은 속채움 콘크리트와 길이방향 철근으로 보강된 PHC 파일의 휨거동을 매우 우수한 정확도로 평가하는 것으로 나타났다. In this study, flexural tests of prestressed high strength spun concrete (PHC) piles reinforced with infilled concrete and longitudinal rebars were conducted, where the longitudinal rebar ratio and the presence of sludge formed on the inner surface of PHC pile were set as key test variables. A total of six PHC pile specimens were manufactured, and their flexural behaviors including failure mode, crack pattern, longitudinal strain distribution in a section and end slip between external PHC pile and infilled concrete were measured and discussed in detail. The test results revealed that the flexural stiffness and strength increased as the longitudinal rebar ratio became larger, and that the sludge formed on the inner surface of PHC pile did not show any detrimental effect on the flexural performance. In addition to the experimental approach, this study presents a nonlinear flexural analysis model considering compatibility conditions and strain and stress distributions of the PHC piles and infilled concrete. The rationality of the nonlinear flexural analysis model was verified by comparing it with test results, and it appeared that the proposed model well evaluated the flexural behavior of PHC piles reinforced with infilled concrete and longitudinal rebars with a good accuracy.

Size effect in ultra-high-performance concrete beams

Yoo, D.Y.,Banthia, N.,Kang, S.T.,Yoon, Y.S. Pergamon Press 2016 Engineering fracture mechanics Vol.157 No.-

<P>In order to investigate the size effect on the flexural performance of ultra-high performance concrete (UHPC), numbers of UHPC beams with three different sizes, including two with smooth steel fibers with aspect ratios of 65 and 100 and one with twisted steel fibers with an aspect ratio of 100, were fabricated and tested. The beams made of UHPC matrix without fiber were also considered for evaluating the effect of fibers on the size effect. In addition, image analyses at crack surfaces were performed to investigate the size effect on the fiber distribution characteristics and their implication on the size dependent flexural performance. Test results indicated that the flexural performance of UHPC noticeably decreased with an increase in the specimen size, caused by a decrease in the number of fibers and poor fiber orientation. The use of longer steel fibers with a higher aspect ratio was effective in reducing the sensitivity to the size effect of UHPC beams compared with shorter steel fibers. Finally, by applying similar fiber distribution characteristics for all test specimens of different sizes, an insignificant size effect on the flexural strength was obtained for UHPC with 2% by volume of steel fibers. (C) 2016 Elsevier Ltd. All rights reserved.</P>

Experimental and Numerical Study on Flexural Performance of a Novel Steel-Encased Concrete Composite Beam

Li-Lin Cao,Ye-Jun Li,Manicka Dhanasekar,Chun-Hua Lu 대한토목학회 2021 KSCE Journal of Civil Engineering Vol.25 No.5

This paper presents a novel configuration of high strength U-shaped steel-encased concrete composite beam (HUCB) in which shear studs connect concrete and U-shaped steel at top flanges and bottom plate. The junction surface of upper slab and lower portion is strengthened by evenly distributed inserted circular rebar. Two steel reinforcements are arranged in the composite beam along the longitudinal direction to reduce the deformation of encased concrete and provide adequate bending capacity under fire condition. Based on the flexural experiments of five specimens, the test failure pattern, load-deflection relation curves, sectional strain distribution at different height and ultimate flexural performance of the HUCB were obtained and are reported in this research. The experimental results show that the HUCB has high ductility and excellent flexural performance. According to test results of five specimens, new calculation formulae were presented to theoretically analyze the flexural capacity of the HUCB. The theoretical analysis values of flexural capacity according to the proposed calculation formulae are consistent with the test results of all specimens. A three-dimensional finite element model is also established to investigate structural performance of the proposed novel composite beam. Test results of five specimens verify the accuracy and validity of finite element analysis results. Parametric studies of the HUCB under positive bending moment are carried out to further analyse the influence of concrete compressive strength, yield strength of U-shaped steel plate and flange width of concrete slab on the flexural performance of the proposed new composite beam.

고강도철근이 배근된 철근콘크리트 보의 휨성능 평가

홍건호(Hong Geon-Ho) 대한건축학회 2011 大韓建築學會論文集 : 構造系 Vol.27 No.1

Korean building code requirements provide that the yield strength of longitudinal reinforcement shall not exceed 550 ㎫ in flexural members. The purpose of this paper is to evaluate the possibility of yield strength increase up to 600 ㎫ or 700 ㎫ in flexural reinforcement. Total 8 simple beam specimens divided by 3 groups tested for evaluating the flexural performance. Main test variables were yield strength of longitudinal reinforcement, reinforcement ratio and cover thickness. Test data analyzed in the viewpoint of cracking load, ultimate flexural strength, load-deflection relationship, crack progress, failure aspects and ductility. Test results indicate that flexural capacity of the specimen is similar from a standpoint of unit strength-area of reinforcement, but ductility of the specimens with high strength reinforcing bars was reduced in high reinforcement ratio. Flexural stiffness of the specimens with high strength reinforcing bars was also reduced, and this phenomenon is well agreed with the reduction of effective moment of inertia Ie. This paper concluded that flexural strength can be calculated using the present code provision without any change, but deflection checkup will be needed when the flexural member design with high strength reinforcing bars.

알칼리 프리계 급결제를 사용한 강섬유 보강 숏크리트의 성능 평가

백철우,박찬기,전언중,원종필,Baek, Chul-Woo,Park, Chan-Gi,Jun, Oun-Jung,Won, Jong-Pil 한국농공학회 2004 한국농공학회논문집 Vol.46 No.3

Modern underground and tunnel works that the wet type shotcrete is getting widely designed and applied in a large scale project. Further to its applications, the needs of improving the performance of the shotcrete, such as new and developed additives and accelerators fur increasing the performance of shotcrete, become the most important issue in the field. The main objective of this study evaluated to performance of steel fiber reinforced shotcrete using alkali free based accelerator for the durability and high quality of shotcrete. The major test variables are accelerator type and its dosage. One type silicate based accelerator and one type aluminate based accelerator and one type alkali free based accelerator were used. The dosage of accelerators is determined by the manufactures and laboratory test condition. Compressive strength test results showed that the dosage of silicate and aluminate based accelerators caused reduction of mechanical properties of shotcrete. Compressive strength of alkali free based accelerator is more stable than of silicate and aluminate based accelerators. Also, according to the compressive strength and flexural test results, it was found that steel fiber reinforced shotcrete used alkali free based accelerator could attain significant improvement in the mechanical and flexural performance.

Efficient parameters to predict the nonlinear behavior of FRP retrofitted RC columns

Navideh Mahdavi,Hamid Reza Ahmadi,Mahmoud Bayat 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.70 No.6

While fiber-reinforced plastic (FRP) materials have been largely used in the retrofitting of concrete buildings, its application has been limited because of some problems such as de-bonding of FRP layers from the concrete surface. This paper is the part of a wide experimental and analytical investigation about flexural retrofitting of reinforced concrete (RC) columns using FRP and mechanical fasteners (MF). A new generation of MF is proposed, which is applicable for retrofitting of RC columns. Furthermore, generally, to evaluate a retrofitted structure the nonlinear static and dynamic analyses are the most accurate methods to estimate the performance of a structure. In the nonlinear analysis of a structure, accurate modeling of structural elements is necessary for estimation the reasonable results. So for nonlinear analysis of a structure, modeling parameters for beams, columns, and beam-column joints are essential. According to the concentrated hinge method, which is one of the most popular nonlinear modeling methods, structural members shall be modeled using concentrated or distributed plastic hinge models using modeling parameters. The nonlinear models of members should be capable of representing the inelastic response of the component. On the other hand, in performance based design to make a decision about a structure or design a new one, numerical acceptance should be determined. Modeling parameters and numerical acceptance criteria are different for buildings of different types and for different performance levels. In this paper, a new method was proposed for FRP retrofitted columns to avoid FRP debonding. For this purpose, mechanical fasteners were used to achieve the composite behavior of FRP and concrete columns. The experimental results showed that the use of the new method proposed in this paper increased the flexural strength and lateral load capacity of the columns significantly, and a good composition of FRP and RC column was achieved. Moreover, the modeling parameters and acceptance criteria were presented, which were derived from the experimental study in order to use in nonlinear analysis and performance-based design approach.

강판 보강 집성재 보의 휨성능 평가 연구

박금성,이상섭,곽명근 한국공간구조학회 2020 한국공간구조학회지 Vol.20 No.2

In this study, we will develop a hybrid cross-sectional shape of steel inserted type glued-laminated timber that can improve the strength of structural glued-laminated timber and maximize the ductility by using steel plate with excellent tensile and deformation ability. A total of three specimens were fabricated and the flexural performance test was carried out to evaluate the structural performance of the steel inserted type glued-laminated timber. In order to compare the effect of steel inserted glued-laminated timber, one structural glued-laminated timber test specimen composed of pure wood was manufactured. In addition, in order to evaluate the adhesion performance of the steel inserted, one each of a screw joint test specimen and a polyurethane joint test specimen was prepared. As a result, all the specimens showed the initial crack in the finger joint near the force point. This has been shown to be a cause of crack diffusion and strength degradation. The use of finger joints in the maximum moment section is considered to affect the strength and ductility of the glued-laminated timber beam. Polyurethane-adhesive steel inserted glued-laminated timber showed fully-composite behavior with little horizontal separation between the steel plate and glued-laminated timber until the maximum load was reached. This method has been shown to exhibit sufficient retention bending performance.

강재 전단 연결재가 사용된 CLT-콘크리트 합성바닥판의 휨성능 평가

박금성(Park, Keum-Sung),오근영(Oh, Keunyeong) 대한건축학회 2021 대한건축학회논문집 Vol.37 No.10

The purpose of this study was to evaluate the flexural performance of CLT-concrete composite floors that used steel shear connectors for applying a light modular system. The proposed steel shear connectors are inverted U-shaped and T-shaped, and were installed in the notches of the CLT floor. As experimental variables, the shear connector types, the number and thickness of CLT layers were considered, and the flexural performance of six composite floor specimens was evaluated. As a result, the maximum loads of all specimens were determined by rolling shear fractures and the specimens using the inverted U-shaped shear connector showed excellent flexural performance. However, the composite effect between CLT and concrete was found to be insignificant, and it is considered that it is necessary to improve the shape of steel shear connector later.

Experimental evaluation on the seismic performance of high strength thin-walled composite members accounting for sectional aspect ratio effect

H. L. Hsu,J. L. Juang,K. T. Luo 국제구조공학회 2009 Steel and Composite Structures, An International J Vol.9 No.4

This study focuses on the experimental evaluation of the flexural-torsional performance of high strength thin-walled composite members. A series of tests on composite members with various sectional aspect ratios subjected to eccentric cyclic loads were conducted. Test results show that the composite member’s torsional strength could be approximated using a series of linear segments and evaluated using the superposition of the component steel and reinforced concrete responses. It is also validated from the tests that the strength deterioration of members subjected to combined loads is closely related to the aspect ratios of the sections. An interaction expression between the bending and torsion for high strength thin-walled composite members is proposed for engineering practice references.