• Journal of the Korea Concrete Institute
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• v.19 no.3
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• pp.253-263
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• 2007

Previous researches showed that confined concrete with Fiber-Reinforced Plastic (FRP) sheets significantly improves the strength and ductility of concrete compared with unconfined concrete. However, the retrofit design of concrete with FRP materials requires an accurate estimate of the performance enhancement due to the confinement mechanism. The object of this research is to predict the compressive strength and strain of concrete confined with FRP wraps. For the purpose of this research, 102 test specimens were fabricated and loaded statically under uniaxial compression. Axial load, axial and lateral strains were investigated to predict the ultimate stress and strain. Also, to achieve reliability of proposed strength and strain models for FRP-confined concrete, another series of uniaxial compression test results were used. This paper presents strength and strain models for FRP-confined concrete. The proposed models to estimate the ultimate stresses and failure strains produce satisfactory predictions as compared to current design equations. In conclusion, it is proposed that the modified stress-strain model of concrete cylinders could be effectively used for the repair and retrofit of concrete columns.

• International Journal of Concrete Structures and Materials
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• v.11 no.1
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• pp.171-183
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• 2017

Strengthening reinforced concrete (RC) beams with openings by using aramid fiber reinforcement polymers (AFRP) on the beams' surfaces offers a useful solution for upgrading concrete structures to carry heavy loads. This paper presents a repairing technique of the AFRP sheets that effectively strengthens RC beams, controls both the failure modes and the stress distribution around the beam chords and enhances the serviceability (deflection produced under working loads be sufficiently small and cracking be controlled) of pre-cracked RC beams with openings. To investigate the possible damage that was caused by the service load and to simulate the structure behavior in the site, a comprehensive experimental study was performed. Two unstrengthened control beams, four beams that were pre-cracked before the application of the AFRP sheets and one beam that was strengthened without pre-cracking were tested. Cracking was first induced, followed by repair using various orientations of AFRP sheets, and then the beams were tested to failure. This load was kept constant during the strengthening process. The results show that both the preexisting damage level and the FRP orientation have a significant effect on strengthening effectiveness and failure mode. All of the strengthened specimens exhibited higher capacities with capacity enhancements ranging from 21.8 to 66.4%, and the crack width reduced by 25.6-82.7% at failure load compared to the control beam. Finally, the authors present a comparison between the experimental results and the predictions using the ACI 440.2R-08 guidelines.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.6
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• pp.154-163
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• 2006

This paper presents a nonlinear analysis method for the reinforced concrete beams strengthened by the external bonding of high strength, lightweight fiber sheets on the tension face of the beams. The method is based on the results of experimental studies. The experimental study involved tensile tests of 120 specimens to evaluate the tensile properties of fiber sheets(carbon, glass, and aramid fiber) and bending tests of 75 beams strengthened with various types of fiber sheets to evaluate the flexural capacities. Based on these experimental results, reasonable rupture strains of the fiber sheets were estimated. The nonlinear flexural analysis considered nonlinear flexural stresses as compressive and tensile stresses of concrete, load-deflection curves, and rupture strains of fiber sheets. The nonlinear flexural analysis accurately predicts the load-deflection response and the flexural behavior of the retrofitted beams.

• Textile Coloration and Finishing
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• v.29 no.2
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• pp.97-103
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• 2017

Polyketone fiber, a newly developed high strength fiber, has a tenacity and modulus similar to the p-aramid fiber, and can be used for reinforcing mechanical rubber goods(MRG), such as tires, hoses, and technical textiles. It will be expected for replacement of super fiber such as aramids and increasing the technical textile market share. This paper surveys the mechanical properties of polyketone fiber for technical textiles. For this purpose, dyed polyketone fabric is prepared, mechanical properties of coated and uncoated polyketone fabrics such as tensile strength, elongation and tear strength were examined before and after weather resistance test(temperature $63{\pm}3^{\circ}C$, humidity 60%, amount of power $0.35w/m^2$). The differences of mechanical properties between uncoated and coated fabrics for high functional technical textiles and composite materials are estimated through this study. The UV-stability of polyketone fabric showed obvious improvement after coating. After 168h(7day) of UV exposure, the coated fabric showed less deterioration in mechanical properties with the retained tensile strength and elongation at break greater than 22 and 17% of the uncoated polyketone fabrics values, respectively.

• Tribology and Lubricants
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• v.39 no.6
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• pp.235-243
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• 2023

This paper presents the fabrication process of water-lubricated plastic bearings. Plastic bearings require good mechanical properties and tribological properties as well as elasticity and shock resistance, especially when lubricated in dirty water conditions. In this study, sleeve-type plastic bearings are produced by winding a prepreg sheet, which primary contains nitrile rubber (NBR)-modified epoxy, self-lubricating fillers, and various types of lattice-structured reinforcing fibers such as carbon, Aramid, and polyethylene terephthalate. A thermosetting epoxy is chemically modified with NBR to impart elasticity and low-friction characteristics in water conditions. Experimental investigations are conducted to examine the mechanical and tribological characteristics of the developed bearing materials, and the results are compared with the characteristics of a commercial plastic bearing (Thordon SXL), well known as a water-lubricated bearing. A Thordon bearing (mainly composed of polyurethane) exhibits an extremely low load-bearing capacity and is thus only suitable for medium loading (1~10MPa). The tribological characteristics of the test materials are evaluated through Falex block-on-ring (LFW-1) friction and wear tests. The results indicate that friction exhibited by the carbon-fiber-reinforced NBR-10wt.%-modified epoxy composite material, incorporated with the addition of 20wt.% UHMWPE and 6wt.% paraffin wax, is lower than that of the Thorden bearings, whereas its wear resistance surpass that of Thorden ones. Because of these features, the load carrying capacity of the fabricated composite (>10MPa) is higher than that of the Thorden bearings. These results confirm the applicability of water-lubricated plastic bearing materials developed in this study.

• Textile Coloration and Finishing
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• v.21 no.6
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• pp.1-11
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• 2009

Super-hydrophobic surface, with a water contact angle greater than $150^{\circ}$, has a self cleaning effect termed 'lotus effect'. We introduced super-hydrophobicity onto aramid/rayon mixture fabric with dual-scale structure by assembling silica nano-sol. Mixture fabric was treated with silica nano-sol, fluoric polymer using various parameters such as particle size, concentration. Silica nano-sol size were measured using particle size analyzer. Morphological changes by particle size were observed using field emission scanning electron microscopy(FE-SEM), contact angle measurement equipment. The contact angle of water was about $134.0^{\circ}$, $137.0^{\circ}$, $143.0^{\circ}$, $139.5^{\circ}$ and $139.0^{\circ}$ for mixture fabric coated with 100.2nm, 313.7nm, 558.2nm, 628.5nm and 965.4nm silica nano-sol, compared with about $120.0^{\circ}$ for mixture fabric coated with fluoric polymer. When we mixed particle sizes of 100.2nm and 558.2nm by 7:3 volume ratio, the contact angle of water was about $146.2^{\circ}$. And we mixed particle sizes of 313.7nm and 558.2nm by 7:3 volume ratio, the contact angle of water was about $141.8^{\circ}$. Also we mixed particle sizes of 558.2nm and 965.4nm by 7:3 volume ratio, the best super-hydrophobicity was obtained. In this paper, we fabricated the water-repellent surfaces with various surface structures by using four types of silica nano-sol, and we found that the dual-scale structure was very important for the super-hydrophobicity.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.2
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• pp.151-160
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• 2017

Growing demand and rapid development of the synthetic fiber rope in mooring system have taken place since it has been used in deep water platform lately. Unlike a chain mooring, synthetic fiber rope composed of lightweight materials such as Polyester(polyethylene terephthalate), HMPE(high modulus polyethylene) and Aramid(aromatic polyamide). Non-linear stiffness and another failure mode are distinct characteristics of synthetic fiber rope when compared to mooring chain. When these ropes are exposed to environmental load for a long time, the length of rope will be increased permanently. This is called 'the creep phenomenon'. Due to the phenomenon, The initial characteristics of mooring systems would be changed because the length and stiffness of the rope have been changed as time goes on. The changed characteristics of fiber rope cause different mooring tension and vessel offset compared to the initial design condition. Commercial mooring analysis software that widely used in industries is unable to take into account this phenomenon automatically. Even though the American Petroleum Institute (API) or other classification rules present some standard or criteria with respect to length and stiffness of a mooring line, simulation guide considers the mechanical properties that is not mentioned in such rules. In this paper, the effect of creep phenomenon in the fiber rope mooring system under specific environment condition is investigated. Desiged mooring system for a Mobile Offshore Drilling Unit(MODU) with HMPE rope which has the highest creep is analyzed in a time domain in order to investigate the effects creep phenomenon to vessel offset and mooring tension. We have developed a new procedure to an analysis of mooring system reflecting the creep phenomenon and it is validated through a time domain simulation using non-linear mooring analysis software, OrcaFlex. The result shows that the creep phenomenon should be considered in analysis procedure because it affects the length and stiffness of synthetic fiber rope in case of high water temperature and permanent mooring system.