• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.1
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• pp.78-85
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• 2023

This study evaluates the performance of reinforced concrete columns using hybrid fiber sheets for structural behavior. The purpose of this method is to improve the load-bearing capacity of the reinforced structure by impregnating a hybrid fiber sheet, which is woven by arranging aramid and glass fibers uniaxially and attached to an aged concrete structure requiring reinforcement with epoxy. In particular, not only the weight reduction of the material obtained by using a fiber lighter than the steel material, but also the low-strength, high-toughness fiber element among the fibers used delays the brittle fracture of the high-strength, low-toughness fiber element. The low-strength, high-toughness fiber element among the fibers used delays the brittle fracture of the high-strength, low-toughness fiber element, resulting in weight reduction compared to steel. The study conducted structural tests on four specimens, with the hybrid reinforcement method and failure mode as main variables. Specimen size and loading conditions were chosen to be comparable with previous studies. The structural performance of the specimen was evaluated using energy dissipation capacity and ductility. Analysis shows that excellent results can be obtained with the hybrid fiber sheet reinforcement.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.1
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• pp.53-58
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• 2017

FRP Hybrid Bar, composed of an embedded steel and the coated composites with epoxy and glass fiber, is an effective construction material with tension-hardening performance and lightweight. The epoxy exposed to UV(Ultra Violet Rays) and FT(Freezing and Thawing) action easily shows a surface deterioration, which can cause degradation of bonding strength between inside-steel and outside-concrete. In the present work, surface inspection for 3 different samples of normal steel, FRP Hybrid Bar before UV, and FRP Hybrid Bar after UV test was performed, then concrete samples with 3 reinforcement types were prepared for accelerated FT test. Through visual inspection on 3 typed reinforcement, no significant deterioration like chalking was evaluated. The results from FT test to 120 and 180 cycles showed FRP Hybrid Bar exposed to UV test has higher bonding strength than normal steel by 106.3% due to enlarged bond area by silica coating. The 3 cases showed a similar bond strength tendency with increasing FT cycles, however a relatively big deviations of bond strength were evaluated in FRP Hybrid Bar after UV test due to loss of silica coating.

• Elastomers and Composites
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• v.53 no.3
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• pp.175-180
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• 2018

Solution-styrene-butadiene rubber (SSBR) composites were manufactured using four kinds of fillers: silica-silane coated carbon black (SC-CB) hybrid, starch-SC-CB hybrid, pure silica, and pure starch. The influence of filler type on the mechanical properties of the rubber matrix was studied in this work. SC-CB was prepared by silane-graft-coating using vinyl triethoxy silane and carbon black, which enhanced the dispersion effect between the rubber matrix and the filler, and improved the mechanical properties of the compounds. The morphology of the composites was observed by field-emission scanning electron microscopy (FE-SEM). The thermal decomposition behavior of the composites was determined by thermogravimetric analysis (TGA), and the crosslinking behavior of the composites was tested using a rubber process analyzer (RPA). The hardness, tensile strength, swelling ratio, and gas transmittance rate of the composites were evaluated according to ASTM. The test results revealed that with the addition of SC-CB, the hybrid fillers, especially those blended with silica, showed a better reinforcement effect, the highest hardness and tensile strength, and stable thermal decomposition behavior. This implies that the silica-SC-CB hybrid filler has a notable mechanical reinforcement effect on the SSBR matrix. Because of self-crosslinking during its synthesis, the starch-SC-CB hybrid filler produced the most dense matrix, which improved the anti-gas transmittance property. The composites with the hybrid fillers had better anti-swelling properties as compared to the neat SSBR composite, which was due to the hydrophilicity of silica and starch.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.13-16
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• 2008

In a tension-controlled section, all steel tension reinforcement is assumed to yield at ultimate when using the strength design method to calculate the nominal flexural strength of members with steel reinforcement arranged in multiple layers. Therefore, the tension force is assumed to act at the centroid of the reinforcement with a magnitude equal to the area of tension reinforcement times the yield strength of steel. Because FRP materials have no plastic region, the stress in each reinforcement layer will vary depending on its distance from the neutral axis. Similarly, if different types of FRP bars are used to reinforce the same member, the stress level in each bar type will vary, and the member will show different behavior from our expectation. In this study, six high-strength concrete beam specimens reinforced with conventional steels, CFRP bars, and GFRP bars as flexural reinforcements were constructed and tested. The members reinforced with hybrid reinforcements showed higher stiffness, smaller crack width, and better ductility than the members reinforced with single type of FRP bars.

• Journal of Fisheries and Marine Sciences Education
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• v.9 no.2
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• pp.188-197
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• 1997

The fracture toughness of three different kinds of epoxy-matrix composites containing the same volume fraction of reinforcement and the variation of fracture toughness of glass-carbon fiber/epoxy hybrid composites due to the change of test temperature and different glass fiber content were investigated in this study. Glass fiber/epoxy composite provided much higher fracture toughness than that of other composites because of the high strain at failure of glass fiber. Particularly the carbon fiber/epoxy composite exhibited the low fracture toughness caused by the low strain energy absorbing capacity of carbon fiber. And it was found that the strain at failure of reinforcement and interfacial delamination absorbing a significant amount of impact energy played an important role to increase fracture toughness of composites. The fracture toughness of the glass-carbon fiber hybrid composites increased with increasing the glass fiber content and decreased with raising the test temperature. The residual stress arising from the different thermal expansion between the matrix and reinforcement influenced the fracture toughness of composites.

• Journal of Korean Association for Spatial Structures
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• v.23 no.1
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• pp.45-52
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• 2023

This study proposes an RCS composite damping device that can achieve seismic reinforcement of existing buildings by dissipating energy by inelastic deformation. A series of experiments assessing the performances of the rubber core pad, hysteretic steel slit damping device, and hybrid RCS damping device were conducted. The results showed that the ratios of the deviations to the mean values satisfied the domestic damping-device conformity condition for the load at maximum device displacement in each direction, at the maximum force and minimum force at zero displacement, as well as the hysteresis curve area. In addition, three analysis models based on load-displacement characteristics were proposed for application to seismic reinforcement design. In addition, the validity of the three proposed models was confirmed, as they simulated the experimental results well. Meanwhile, as the shear deformation of the rubber-core pad increased, the hysteretic behavior of super-elasticity greatly increased the horizontal force of the damping device. Therefore, limiting the allowable displacement during design is deemed to be necessary.

• Advances in Computational Design
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• v.8 no.4
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• pp.295-307
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• 2023

This paper presents an optimization of the reinforced concrete ribbed slab in terms of minimum CO₂ emissions and an economic justification of the final optimal design. The design variables are six geometry variables including the slab thickness, the ribs spacing, the rib width at the lower and toper end, the depth of the rib and the bar diameter of the reinforcement, and the seventh variable defines the concrete strength. The objective function is considered to be the minimum amount of carbon dioxide gas (CO₂) emission and at the same time, the optimal design is economical. Seven significant design constraints of American Concrete Institute's Standard were considered. A robust metaheuristic optimization method called improved dolphin echolocation and ant colony optimization (IDEACO) has been used to obtain the best possible answer. At optimal design, the three most important sources of CO₂ emissions include concrete, steel reinforcement, and formwork that the contribution of them are 63.72, 32.17, and 4.11 percent respectively. Formwork, concrete, steel reinforcement, and CO₂ are the four most important sources of cost with contributions of 67.56, 19.49, 12.44, and 0.51 percent respectively. Results obtained by IDEACO show that cost and CO₂ emissions are closely related, so the presented method is a practical solution that was able to reduce the cost and CO₂ emissions simultaneously.

• Structural Engineering and Mechanics
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• v.78 no.4
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• pp.387-401
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• 2021

This paper provides a methodology to analyze the seismic performance of different component designs in hybrid masonry structures (HMS). HMS, comprised of masonry panels, steel frames and plate connectors is a relatively new structural system with potential applications in high seismic areas. HMS dissipate earthquake energy through yielding in the steel components and damage in the masonry panels. Currently, there are no complete codes to assist with the design of the energy dissipation components of HMS and there have been no computational studies performed to aid in the understanding of the system energy dissipation mechanisms. This paper presents parametric studies based on calibrated computational models to extrapolate the test data to a wider range of connector strengths and more varied reinforcement patterns and reinforcement ratios of the masonry panels. The results of the numerical studies are used to provide a methodology to examine the effect of connector strength and masonry panel design on the energy dissipation in HMS systems. We use as test cases two story structures subjected to cyclic loading due to the availability of experimental data for these configurations. The methodology presented is however general and can be applied to arbitrary panel geometries, and column and story numbers.

• Computers and Concrete
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• v.31 no.3
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• pp.197-206
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• 2023

In this paper, the bending performance of a MSFRHPC (containing steel fiber, polyvinyl alcohol (PVA) fiber, and CW)-reinforced beam was studied for the first time. Introducing a multiscale fiber system increased the first crack load (up to 150%), yield load (up to 50%), and peak load (up to 15%) of reinforced beams. The multiscale fiber system delays cracking of the reinforced beam, reduces crack width of the reinforced beam in normal use, and improves the durability of the beam. Considering yield load and peak load, the reinforcing effect of multiscale fiber on the high-reinforcement ratio beam (1.00%) is better than that on the low-reinforcement ratio beam (0.57%). Introducing fibers slowed the development of cracks in the reinforced beam under bending. With the added hybrid fiber, the deformation concentration of reinforced beams after yield was more significant with concentration in 1 or 2 cracks. A model for predicting the flexural capacity of MSFRHPC-reinforced beams was proposed, considering the action of multiscale hybrid fibers. This research is helpful for structure application of MSFRHPC-containing CW.

• Journal of the Korean Wood Science and Technology
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• v.51 no.6
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• pp.526-541
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• 2023

Wooden structures are widely used, particularly in earthquake zones, owing to their light weight, ease of application, and resistance to the external environment. In this study, we aimed to improve the mechanical properties of laminated timber beams using novel hybrid systems [carbon-fiber-reinforced polymer (CFRP) and wire rope]. Within the scope of this study, it is expected that using wood, which is an environmentally friendly and sustainable building element, will be more economical and safe than the reinforced concrete and steel elements currently used to pass through wide openings. The structural behavior of the hybrid-reinforced laminated timber beams was determined under the loading system. The experimental findings showed that the highest increase in the values of laminated beams reinforced with steel ropes was obtained with the 2N reinforcement, with a maximum load of 38 kN and a displacement of 137 mm. Thus, a load increase of 168% and displacement increase of 275% compared with the reference sample were obtained. Compared with the reference sample, a load increase of 92% and a displacement increase of 14% were obtained. Carbon fabrics placed between the layers with fiber-reinforced polymer (FRP) prevented crack development and provided significant interlayer connections. Consequently, the fabrics placed between the laminated wooden beams with the innovative reinforcement system will not disrupt the aesthetics or reduce the effect of earthquake forces, and significant reductions can be achieved in these sections.