• Journal of The Korean Society of Agricultural Engineers
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• v.46 no.1
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• pp.41-51
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• 2004

FRP re-bar in concrete structures could be used as a substitute of steel re-bars for that cases in which aggressive environment produce high steel corrosion, or lightweight is an important design factor, or transportation cost increase significantly with the weight of the materials. But FRP fibers have only linearly elastic stress-strain behavior; whereas, steel re-bar has linear elastic behavior up to the yield point followed by large plastic deformation and strain hardening. Thus, the current FRP re-bars are not suitable concrete reinforcement where a large amount of plastic deformation prior to collapse is required. The main objectives of this study in to evaluate the tensile behavior and the fracture mode of hybrid FRP re-bar. Fracture mode of hybrid FRP re-bar is unique. The only feature common to the failure of the hybrid FRP re-bars and the composite is the random fiber fracture and multilevel fracture of sleeve fibers, and the resin laceration behavior in both the sleeve and the core areas. Also, the result of the tensile and interlaminar shear stress test results of hybrid FRP re-bar can provide its excellent tensile strength-strain and interlaminar stress-strain behavior.

• Computers and Concrete
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• v.33 no.2
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• pp.163-173
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• 2024

Fiber-reinforced polymers (FRP) have a proven strength enhancement capability when installed into Reinforced Concrete (RC) beams. The brittle failure of traditional FRP strengthening systems has attracted researchers to develop novel materials with improved strength and ductility properties. One such material is that known as polyethylene terephthalate (PET). This study presents a numerical investigation of the flexural behavior of reinforced concrete beams externally strengthened with PET-FRP systems. This material is distinguished by its large rupture strain, leading to an improvement in the ductility of the strengthened structural members compared to conventional FRPs. A three-dimensional (3-D) finite element (FE) model is developed in this study to predict the load-deflection response of a series of experimentally tested beams published in the literature. The numerical model incorporates constitutive material laws and bond-slip behavior between concrete and the strengthening system. Moreover, the validated model was applied in a parametric study to inspect the effect of concrete compressive strength, PET-FRP sheet length, and reinforcing steel bar diameter on the overall performance of concrete beams externally strengthened with PET-FRP.

• Journal of the Korea Concrete Institute
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• v.23 no.4
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• pp.511-520
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• 2011

Recent studies to improve reinforcement of structures have developed stiff type Polyurea by using highly polymized compound Polyurea, but the reinforcing effect of it appears to be merely good. To find the proper usage of Polyurea as structural reinforcement, stiff type Polyurea has developed by manipulating the ratio of the components that consist flexural type Polyurea and the developed stiff type Polyurea shows higher hardness and tensile capacity. The reinforcement effect evaluation of has been performed by the polyurea applied RC slab specimens, and the reinforcement effect of the combination of fiber sheet and polyurea has been tested. The results shows that the Polyurea applied specimens have significant improvement on hardness and ductility compare to those of unreinforced. Also, the specimens that stiff type Polyurea is sprayed on fiber sheet reinforcement has higher reinforcing effect than only sheet reinforced specimens. However, the specimens that and fiber sheet attached after polyurea applied on showed that the high toughness of fiber sheet restrains the ductile behavior of Polyurea due to the high ductility, thereby the specimen suffers the concentration of load, which leads the brittle fracture behavior.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.1
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• pp.45-52
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• 2015

Fiber-reinforced polymer (FRP) has been generally accepted by civil engineers as an alternative for steel reinforcing bars (rebar) due to its advantageous specific tensile strength and non-corrosiveness. Even though some glass fiber reinforced polymer (GFRP) rebars are available on a market, GFRP is still somewhat uncompetitive over steel rebar due to their high cost and relatively low elastic modulus, and brittle failure characteristic. If the price of component materials of GFRP rebar is not reduced, it would be another solution to increase the performance of each material to the highest degree. The tensile strength generally decreases with increasing diameter of FRP rebar. One of the reasons is that only fibers except for fibers in center resist the external force due to the lack of force transfer and the deformation of only outer fibers by gripping system. Eliminating fibers in the center, which do not play an aimed role fully, are helpful to reduce the price and finally FRP rebar would be optimized over the price. In this study, the effect of the hollow section in a cross-section of a GFRP rebar was investigated. A GFRP rebar with 19 mm diameter was selected and an analysis was performed for the tensile test results. Parameter was the ratio of hollow section over solid cross-section. Four kinds of hollow sections were planned. A total of 27 specimens, six specimens for each hollow section and three specimens with a solid cross-section were manufactured and tested. The change by the ratio of hollow section over solid cross-section was analyzed and an optimized cross-section design was proposed.

• Advances in concrete construction
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• v.7 no.4
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• pp.249-262
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• 2019

In this study, high strength aluminum alloys (AA) plates are proposed as a new construction material for strengthening reinforced concrete (RC) beams. The purpose of this investigation is to evaluate AA plate's suitability as externally bonded reinforcing (EBR) materials for retrofitting shear deficient beams. A total of twenty RC beams designed to fail in shear were strengthened with different spacing and orientations. The specimens were loaded with four-points loading till failure. The considered outcome parameters included load carrying capacity, deflection, strain in plates, and failure modes. The results of all tested beams showed an increase up to 37% in the load carrying capacity and also an increase in deflection compared to the control un-strengthened beams. This demonstrated the potential of adopting AA plates as EBR material. Finally, the shear contribution from the AA plates was predicted using the models available in the ACI440-08, TR55 and FIB14 design code for fiber reinforced polymer (FRP) plates. The predicted results were compared to experimental testing data with the ratio of the experimentally measured ultimate load to predicted load, range on the average, between 93% and 97%.

• Composites Research
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• v.34 no.1
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• pp.8-15
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• 2021

In the shipbuilding and marine industry, as a technology for reducing the weight of parts to reduce energy and improve operational efficiency of ships is required, a method of applying fibers-reinforced composites which is high-strength lightweight materials, as part materials can be considered. In this study, the possibility of applying fibers-reinforced composites to the pipe support clamps was evaluated to reduce the weight of LNGC. The fibers-reinforced composites were manufactured using carbon fibers and glass fibers as reinforcing fibers. Through the computer simulation program, the properties of the reinforcing materials and the matrix materials of the composites were inversely calculated, and the performance prediction was performed according to the change in the properties of each fiber lamination pattern. In addition, the structural analysis of the clamps according to the thickness of the composites was performed through the finite element analysis program. As a result of the study, it was confirmed that attention is needed in selecting the thickness when applying the fibers-reinforced composites of the clamp for weight reduction. It is considered that it will be easy to change the shape of the structure and change the structure for weight reduction in future supplementary design.

• International Journal of Industrial Entomology and Biomaterials
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• v.26 no.2
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• pp.81-88
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• 2013

Wet-spun silk fibers have attracted the attention of many researchers because of 1) the unique properties of silk as a biomaterial, including good biocompatibility and cyto-compatability and 2) the various methods available to control the structure and properties of the fiber. Cellulose nanofibrils (CNFs) have typically been used as a reinforcing material for natural and synthetic polymers. In this study, CNF-embedded silk fibroin (SF) nanocomposite fibers were prepared for the first time. The effects of CNF content on the rheology of the dope solution and the characteristics of wet-spun CNF/SF composite fibers were also examined. A 5% SF formic acid solution that contained no CNFs showed nearly Newtonian fluid behavior, with slight shear thinning. However, after the addition of 1% CNFs, the viscosity of the dope solution increased significantly, and apparent shear thinning was observed. The maximum draw ratio of the CNF/SF composite fibers decreased as the CNF content increased. Interestingly, the crystallinity index for the silk in the CNF/SF fibers was sequentially reduced as the CNF content was increased. This phenomenon may be due to the fact that the CNFs prevent ${\beta}$-sheet crystallization of the SF by elimination of formic acid from the dope solution during the coagulation process. The CNF/SF composite fibers displayed a relatively smooth surface with stripes, at low magnification (${\times}500$). However, a rugged nanoscale surface was observed at high magnification (${\times}10,000$), and the surface roughness increased with the CNF content.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.183-186
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• 1999

Up to date, it is difficult to estimate the consistence of properties on the epoxy liner in service time because an estimation of the long term environment-deterioration with aging has not been processed. In the study, the estimation on epoxy liner is carried by the physical test 7 rounds. There are the elongation the and the crack bridging test in the part of physical tests. An elongation test is carried out with epoxy membrane and a crack bridging test is carried out with specimen painted epoxy on concrete. The subjects of test and estimation are a containment quality system and a fibre-glass reinforced system. The materials of these systems are a Robber added Epoxy, a Silica added Epoxy, and a Fiber reinforced Epoxy. Ensuring the test data, properties of epoxy liner was estimated and the change of properties was predicted on epoxy liners.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.636-639
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• 2004

Reinforced concrete structures have been used for a long time. However, corrosion problem in reinforcing steel is inevitable, which results in the degradation of performance and the shortening of the life of structures. To overcome such problems, FRP(Fiber Reinforced Polymer) rebars have been developed. Due to their corrosion resistance and their superior mechanical properties, FRP rebars are increasingly applied to concrete structures in other countries. To obtain the composite action between FRP rebars and concrete, sufficient bond between two materials must be secured. But, the behavior of FRP rebars is different from that of steel rebars. Therefore, it is necessary to understand and develop the proper bond mechanism of FRP rebars to use them in concrete structures. This paper presents analytical results to investigate the bond-slip relationship between FRP rebars and concrete based on pull out tests.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.329-332
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• 2005

R.C. bridges may require strengthening during the service life. The main cause of durability problem of R.C. bridges is the corrosion of reinforcing steel. For this reason, researches to solve the problem have been conducted but the achievements are just for improving, not the solution. Fiber Reinforced Polymers are recognized as the alternative materials for solving the problem due to the excellent corrosion-resistant property, light-weight and higher strength than steel. This paper presents experimental results and theoretical consideration of bond test for new type GFRP rebar