• Journal of Ocean Engineering and Technology
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• v.13 no.3B
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• pp.56-64
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• 1999

An experimental study was carried out to examine the structural behavior of reinforced concrete deep beams strengthened with aramid fiber sheets, carbon fiber sheets and plates, and to propose the reasonable strengthening method for the deteriorated R.C. deep beams. Results show that the most significant differences in behavior of reinforced concrete deep beams strengthened with fiber sheet and plate were mainly due to various fiber orientations and anchorage. Deep beams diagonally strengthened with carbon fibers show better performance compared with those of vertically, horizontally strengthened specimens and produce the increase in the shear resistance through the redistribution of internal forces after the initial cracks occur. However, strengthened deep beams without anchorages might show unreasonable, brittle peeling-off failure of fiber reinforcements.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.5
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• pp.163-169
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• 2017

Although the strength of polyethylene terephthalate (PET) fibers which are generally used to make plastic bottles is low, the deformability of PET fibers is substantially high. Due to these material characteristics, a PET fiber can be used as a reliable strengthening material to resist a large deformation caused by earthquake and research pertinent to application of PET fibers is actively conducted in Japan. Therefore, in this study, experiments have been carried out to investigate the lateral confinement effect of PET fibers and to assess the applicability of PET fibers to construction fields by comparing the strengthening effect of PET fibers to that of carbon and glass fiber sheets. For this purpose, concrete cylinder specimens with parameters of different concrete strength and strengthening layers of carbon fiber sheets, glass fiber sheets, and PET fibers were respectively tested using two sets of cylinders for each parameter. As a result, specimens strengthened with carbon fiber sheets and glass fiber sheets failed due to sudden decrease of strength as with existing studies. However, specimens with PET fibers reached their maximum strength and then failed after gradual decrease strength without failure of PET fibers. In addition, although the strength of specimens with PET fibers did not significantly increase in comparison with that of specimens with carbon fiber sheets and glass fiber sheets, specimens with PET fibers indicated considerable deformability. Thus, a PET fiber can be considered as an effective strengthening material.

• International Journal of Concrete Structures and Materials
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• v.8 no.1
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• pp.27-41
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• 2014

The use of carbon fibers (CF) and glass fibers (GF) were combined to strengthen concrete flexural members. In this study, data of tensile tests of 94 hybrid carbon-glass FRP sheets and 47 carbon and GF rovings or sheets were thoroughly investigated in terms of tensile behavior. Based on comparisons between the rule of mixtures and test data, positive hybrid effects were identified for various (GF/CF) ratios. Unlike the rule of mixtures, the hybrid sheets with relatively low (GF/CF) ratios also produced pseudo-ductility. From the calibrated results obtained from experiments, a new analytical model for the stress-strain relationship of hybrid FRP sheets was proposed. Finally, the hybrid effects were verified by structural tests of concrete members strengthened with hybrid FRP sheets and either carbon or glass FRP sheets.

• Journal of the Korean Society of Safety
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• v.14 no.1
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• pp.129-140
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• 1999

This study presents test results of RC beams strengthened by steel plates, carbon fiber sheets(CFS) and aramid fiber sheets(AFS) for increasing flexural and shear resistance. The test was performed with different parameters including the type of strengthening materials, flexural-strengthening methods and shear-strengthening methods. In case of flexural test, RC beams are initially loaded to 70% of the ultimate flexural capacity and in case of shear test loaded to 60 or 80 percent of the ultimate shear capacity and subsequently reinforced with steel plates, CFS and AFS. Experimental data on strength, steel strain, deflection, and mode of failure of the reinforced beams were obtained, and comparisons between the different shear reinforced schemes and the non-strengthened control beams were made. The test results showed that damaged RC beams strengthened by steel plates, CFS and AFS have more improved the flexural and shear capacity. For the beams with external reinforcement by steel plates, aramid fiber sheets and carbon fiber sheets increases in ultimate strength of 4 to 21, 17 to 43 and 26 to 36 percent were respectively achieved. Initial load had small effect on strength after reinforcement, but an important influence on deflection. One sheet reinforced was stronger than two sheets reinforced but less deflected than two sheets reinforced.

• Computational Structural Engineering : An International Journal
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• v.1 no.1
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• pp.39-48
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• 2001

An analytical compressive stress-strain relationship model for circular and rectangular concrete specimens confined with laminated carbon fiber sheets (CFS) is studied. Tsai-Hill and Tsai-Wu failure criteria were used to implement orthotropic behavior of laminated composite materials. By using these criteria, an algorithm which analyzes the confinement effect of CFS on concrete was developed. The proposed analytical model was verified through the comparison with experimental data. Various parameters such as concrete strength, ply angle, laminate thickness, section shape, and ply stacking sequences were investigated. Numerical results by the proposed model effectively simulate the experimental compressive stress-strain behavior of CFS confined concrete specimens. Also, the pro-posed model estimates the compressive strength of the specimen to a high degree of accuracy.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.3
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• pp.177-187
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• 2004

This investigation attempts to analyze the flexural behavior of a strengthened beam with carbon fiber sheets in three stages according to the conditions of the constituents : elastic stage, pre-yielding stage, and post-yielding stage. The proposed analytical method for strengthened beams is compared with the experimental results such as yield load, ultimate load, and flexural rigidities. The contributions of the constituents to the strengthened beam capacity are examined from the flexural analysis. The validity of using KCI strength method to estimate ultimate moment of a strengthened beam is also investigated.

• Journal of the Korea institute for structural maintenance and inspection
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• v.1 no.1
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• pp.89-96
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• 1997

The paper presents the results of experimental studies on two strengthening methods for reinforced concrete (RC) slabs. Bending tests on RC slabs have been carried out to investigate the influence of the increased thickness and externally bonded carbon fiber sheets. The interfaces of new and old concrete of increased thickness specimens have been chipped and treated with bonding agent. The conclusions have been reached as followings. (1) The behavior of specimens with chipped interface is good enough to calculate flexural strength of RC slabs for increased depth. (2) The flexural stiffness of increased depth specimen is severely increased and the deformation of RC slabs is controled. (3) The specimens with externally bonded carbon fiber sheets can be assumed to behave monolithically.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.1 s.53
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• pp.37-43
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• 2007

Experiments for circular unreinforced concrete beams confined by carbon fiber tubes (CFT) made of carbon fiber sheets were performed. Selected test parameter was thickness of carbon fiber tube: 1.5mm (3 layers), 2.0mm (4 layers), 2.5mm (5 layers), and 3.0mm (6 layers). Based on the test results, an equation for estimating moment capacity of the circular beams confined by carbon fiber tubes was proposed. Comparison results showed good agreement up to 2.5mm (5 sheets) of the CFT thickness.

• Transactions of Materials Processing
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• v.29 no.1
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• pp.27-36
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• 2020

The Goss texture component of {110}<001> is well known as one of the best texture components to improve the magnetic properties of electrical steel sheets. The small amount of the Goss texture component is obtained at the surface of the steel sheet by shear deformation due to friction between the steel sheet and the roll during conventional symmetric rolling. This study aims to identify a method to obtain high intensity of the Goss texture component not only at the surface but in the whole layer of the steel sheet by shear deformation of asymmetric rolling. Low carbon steel sheets, which have different initial texture, were asymmetrically rolled by about 50%, 70%, and 80%. The pole figures of the top, center, and bottom layers of the initial and asymmetrically rolled low carbon steel sheets were measured by an X-ray diffractometer. Based on the measured pole figures of these samples, the intensities of the main texture components were analyzed for the initial and asymmetrically rolled low carbon steel sheets. As a result, the initial low carbon steel sheet with the γ-fiber component showed a higher intensity of the Goss texture component in the whole layer than the steel sheet with other texture components after asymmetric rolling.

• Structural Engineering and Mechanics
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• v.55 no.3
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• pp.511-523
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• 2015

Damaged steel-concrete composite girders can be repaired and retrofitted by epoxy-bonded carbon fiber-reinforced polymer (CFRP) sheets to the critical areas of tension flanges. This paper presents the results of a study on the behavior of damaged steel-concrete composite girders repaired with CFRP sheets under static loading. A total of seven composite girders made of I20A steel sections and 80mm-thick by 900mm-wide concrete slabs were prepared and tested. CFRP sheets and prestressed CFRP sheets were used to repair the specimens. The specimens lost the cross-sectional area of their tension flanges with 30%, 50% and 100%. The results showed that CFRP sheets had no significant effect on the yield loads of strengthened composite girders, but had significant effect on the ultimate loads. The yield loads, elastic stiffness, and ultimate bearing capacities of strengthened composite girders had been changed as a result of prestressed CFRP sheets, the utilization ratio of CFRP sheets could be effectively improved by applying prestress to CFRP sheets. Both the yield loads and ultimate bearing capacities had been changed as a result of steel beam's flange damage level and CFRP sheets could cover the girders' shortage of bearing capacity with 30% and 50% flange damage, respectively.