• Computers and Concrete
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• v.33 no.4
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• pp.385-398
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• 2024

As concrete dominates the construction industry, alternatives to traditionally used steel reinforcement are being sought. This study explored the suitability of carbon fiber-reinforced polymer (CFRP) as a substitute within rigid frames, focusing on its impact on section ductility and overall structural durability against seismic events. However, current design guidelines address quasi-static loads, leaving a gap for dynamic or extreme circumstances. Our approach included multiscale simulations, parametric study, and energy dissipation analyses, drawing upon a unique adaptation of modified compression field theory. In our efforts to optimize macro and microparameters to improve yield strength, manage brittleness, and govern failure modes, we also recognized the potential of CFRP's high corrosion resistance. This characteristic of CFRP could significantly reduce the frequency of required repairs, thereby contributing to enhanced durability of the structures. The research reveals that CFRP's durability and seismic resistance are attributed to plastic joints within compressed fibers. Notably, CFRP can impart ductility to structural designs, effectively balancing its inherent brittleness, particularly when integrated with quasi-brittle materials. This research challenges the notion that designing bendable components with carbon fiber reinforcement is impractical. It shows that creating ductile bending components with CFRP in concrete is feasible despite the material's brittleness. This funding overturns conventional assumptions and opens new avenues for using CFRP in structural applications where ductility and resilience are crucial.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.5
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• pp.41-50
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• 2014

This study evaluated the bonding property of fiber and flexural behavior of fiber reinforced concrete. Amorphous steel fiber, hooked steel fiber and polyamide fiber was used for evaluation of bonding property and flexural behavior. As a result, the hooked steel fiber was pulled out from matrix when peak stress. However amorphous steel fiber occurred shear failure because bonding strength between fiber and matrix was higher than tensile strength of fiber. Polyamide fibers occurred significantly displacement to peak stress because of elongation of fiber. After that peak stress, fiber was cut off. Amorphous steel fiber reinforced concrete had a greater maximum flexural load compared with hooked steel fiber reinforced concrete because bonding performance between fiber and matrix was high and mixed population of fiber was many. However flexural stress was rapidly reduced in load-deflection curve because of shear failure of fiber. Flexural stress of hooked steel fiber reinforced concrete was slowly reduced because fiber was pulled out from the matrix. In the case of polyamide fiber reinforced concrete, flexural stress was rapidly lowered because of elongation of fiber. However flexural stress was increased again because of bonding property between polyamide fiber and matrix. The pull-out properties of the fiber and matrix has effect on the deformation capacity and flexural strength of fiber reinforced concrete.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.3
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• pp.76-83
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• 2014

The purpose of this study is to evaluate the shear strengthening effect of steel fiber in high strength SFRC beams. For this purpose, 13th specimens are prepared and structural tests are performed. Testing variables are shear span to depth ratio, steel fiber volume fraction, shear strengthening ratio in 60 MPa SFRC concrete. From the reviewing of previous researches and analyzing of material and member test results, shear span to depth ratio 2.5 and steel fiber volume fraction 1.0% can be having a maximum strengthening effect in steel fiber. Proposed shear strength estimation equation, which is considering steel fiber strengthening and shear span to depth ratio effect, underestimate the shear capacity of high strength SFRC beams. Therefore a detailed research on strength characteristics of high strength SFRC beams are needed.

• Journal of the Korea Concrete Institute
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• v.24 no.3
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• pp.323-331
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• 2012

This paper presents a new strengthening method on concrete column against seismic loads for structural performance tests. An X-bracing using high performance carbon fiber threads called the "Carbon fiber anchor X-bracing system" is used to connect RC frames internally. The carbon fiber sheet is wrapped around the column to fix the top and bottom of the column after Super anchor was installed by drilling hole on the column. The structural performance was evaluated experimentally and analytically. Two types of columns specimens were made; flexure fracture scaled model and shear fracture scaled model. For the performance evaluation, cyclic loading tests were conducted on moment and shear resisting columns with and without X bracing. Test results confirmed that the bracing system installed on RC columns enhanced the strength capacity and provided adequate ductility.

• Journal of the Korea Institute of Building Construction
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• v.11 no.4
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• pp.326-332
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• 2011

Carbon, Aramid, Boron and Glass fibers are used as fibrous materials to promote structural bearing strength. Of these fiber types, carbon fiber is the most commonly used material, and is characterized by having a one-way direction, which is strengthened by tensile strength due to the attached direction only, while other types of fibers are two-way. Therefore, when applied in the field, the attachment direction of fiber is a very important factor. However, when fiber direction is not mentioned in the design drawing, there sometimes is no improvement in structural strength, as the fiber is being installed by a site engineer or workers who lack structural knowledge. The purpose of this study was to propose an optimal direction of carbon fiber through a comparison & analysis of reinforcing efficiency with reinforced experimental columns that used carbon fibers in each of the inclined, horizontal and vertical directions. According to the results, horizontal direction in the reinforced column was improved by 153.43%, but vertical direction was 104.61% only, and it was understood this was due to increased tensile strength along the fiber direction. For this reason, it is necessary to include information regarding fiber direction in design and site management.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.127-131
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• 2003

KARI developed 50m class unmanned airship. The airship employ the pressure envelope design principle. The envelope must be considered as a main structural element of the airship. The envelope ＆ three ballonets are fabricated by polyfiber composite laminates. Other structural components (gondola, tailwing, nosecone ＆ engine mounts) are manufactured by carbon fiber ＆ glass fiber laminates. In order to develop a big unmanned airship, a large amount of structural design, analysis and tests had to be made. The paper describes the structural configuration of the 50m class uumanned airship which are basic starting point of the structural development of an airship. The paper includes the various designing processes, components development tests and analysis results. Envelope ＆ ballonets development processes which are very different to conventional airplane design are given in details with actual analysis & test results. The paper also describes the structural design and analysis results for other composite made structures. Each components were tested by static design limit loads and structural safety were confirmed. The paper shows the manufactured structural components and assembled airship.

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.759-766
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• 2004

The addition of steel fiber with concrete significantly improves the engineering properties of structural members, notably shear strength. The purpose of this study is to determine the steel fiber shape, aspect ratio and volume fraction ratio in a point of practical usage as structural members. Steel fiber factor and volume fraction are also considered to verify the strengthening effect in member level. From the reviewing of previous researches and analyzing of consecutive material test results, the optimum shape and length of steel fiber, which can have a good strengthening effects were defined as a hooked end type and larger than 1.5 times of maximum gravel size. Analyzing the test results of strength and deformation capacity, aspect ratio 75 and volume fraction $1.5\%$ can be having a maximum strengthening effect of steel fiber. Also steel fiber factor, tensile splitting strength, and flexural strength are found as key parameter in shear strengthening effect in member level.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.4
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• pp.49-56
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• 2015

Ultra-High Strength Concrete(UHPC) has ultra-high material performance including high strength and high flowability. On the other hand it is less ductile than high ductile fiber reinforced cementitious composite. This study investigated the effect of combination of steel fiber and micro fiber on the tensile behavior of UHPC. Four types of UHPC containing combination of steel fiber, polyethylene(PE), polyvinyl alcohol(PVA), and basalt fiber were designed. And then uniaxial tension tests were performed to evaluate the tensile behavior of UHPC according to combination of fibers. And density was measured to evaluate whether micro fiber induces unintentional high pore or not. From the test results, it was exhibited that PE fiber with high strength is effective to improve the tensile behavior of UHPC and basalt fiber is effective to increase the cracking and tensile strength of UHPC. Furthermore, it was also verified that micro fiber does not make high pore.

• Journal of the Korea Concrete Institute
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• v.23 no.1
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• pp.67-75
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• 2011

The effect of steel-fiber contents on the compressive behavior of ultra high performance cementitious composites (UHPCC) was studied to propose a compressive behavior model for UHPCC. The experiments considered fiber contents of 0~5 vol.% and the results indicated that compressive strength and corresponding strain as well as elastic modulus were improved as the fiber contents increased. Compared to the previous study results obtained from concrete with compressive strength of 100MPa or less, the reinforcement effect on strength showed similar tendency, while the effect on the strain and elastic modulus were much less. Strength, strain, and elastic modulus according to the fiber contents were presented as a linear function of fiber reinforcement index (RI). Fiber reinforcement in UHPCC had no influence on the shape of compressive behavioral curve. Considering its effect on compressive strength, strain, and elastic modulus, a compressive stress-strain relation for UHPCC was proposed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.157-163
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• 2018

This study is aimed at controlling the fiber orientation and improve the fiber distribution in fiber-reinforced cement composites using blades that can be placed inside the existing nozzles. To optimize the blade parameters, multi-physics finite element analysis was performed that could account for the flow of the cementitious matrix material, the movement of the entrained fibers, and the interactions with the nozzle. As a result, this study defined the blade distance, length, and position as a function of the fiber length to be used in the field. The blades with a distance from 1.2 to 2.4 times the fiber length and length from 4 to 8 times the fiber length, as well as located at below 14 times the fzfiber length from the nozzle exit maintained the fiber orientation angle less than $5^{\circ}$. In addition, the blade-type nozzle proposed in the study can be attachable and detachable to the conventional casting equipment, and thus it can provide the usability and convenience in practical applications.