• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.2
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• pp.122-129
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• 2019

Cracks in concrete structures are inevitable phenomena caused by shrinkage, hydration heat, and external loads. These cracks facilitate the penetration of external harmful ions into the concrete, which greatly reduces its durability. Recently, self-healing concrete has been actively studied. Also, self-healing fiber-reinforced concrete have been studied to control the crack in concrete and to maximize the shelf-healing capability. In this study, mortar specimens containing PVA fiber, fly ash and crystalline admixture were fabricated. The compressive and flexural strength were evaluated. Also, the self-healing performance was evaluated by the absorption test. From the results, it was confirmed that the amount of water absorbed by healing of the crack decreased as time increased. It was also found that PVA fiber is beneficial for the production of calcium carbonate, an additional healing product.

• Composites Research
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• v.31 no.6
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• pp.304-310
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• 2018

Autoclave process has been remaining as one of the most robust and stable process in fabricating structural composite part of aerospace industry. It has lots of advantages, however exhibits some disadvantages or limitations in capital investment and operation. Recently, there have been various Out-of-Autoclave process being researched and developed to overcome those limitations. In this study, laminate specimens were fabricated using LCM (Liquid Composite Molding) process, regarded as one of potential OoA process. DB (Double bagging), CAPRI (Controlled Atmospheric Pressure Resin Infusion), VAP (Vacuum Assisted Process) and Autoclave process were used for laminate specimens. Void content, Thickness, Tg (Glass Transition Temperature), ILSS (Interlaminar Shear Strength) and Flexural strength properties were evaluated for comparison. It is verified that Autoclave based specimen has uniform thickness distribution, the lowest void content and outstanding mechanical properties. And, CAPRI based specimen exhibits relatively good physical and mechanical properties over DB and VAP based specimen and comparable mechanical properties with autoclave based specimen.

• Steel and Composite Structures
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• v.31 no.4
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• pp.373-385
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• 2019

This paper presents a useful in-plane structural analysis of low-rise blind-bolted composite frames with semi-rigid joints. Analytical models were used to predict the moment-rotation relationship of the composite beam-to-column flush endplate joints that produced accurate and reliable results. The comparisons of the analytical model with test results in terms of the moment-rotation response verified the robustness and reliability of the model. Abaqus software was adopted to conduct frame analysis considering the material and geometrical non-linearities. The flexural behaviour of the composite frames was studied by applying the lateral loads incorporating wind and earthquake actions according to the Australian standards. A wide variety of frames with a varied number of bays and storeys was analysed to determine the bending moment envelopes under different load combinations. The design models were finalized that met the strength and serviceability limit state criteria. The results from the frame analysis suggest that among lateral loads, wind loads are more critical in Australia as compared to the earthquake loads. However, gravity loads alone govern the design as maximum sagging and hogging moments in the frames are produced as a result of the load combination with dead and live loads alone. This study provides a preliminary analysis and general understanding of the behaviour of low rise, semi-continuous frames subjected to lateral load characteristics of wind and earthquake conditions in Australia that can be applied in engineering practice.

• Composites Research
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• v.31 no.6
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• pp.317-322
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• 2018

In various industry, the composite is tried to be applied to products and thermoplastic based composite is in the spotlight because this composite can be recycled. The use of continuous fiber thermoplastic (CFT) method increased gradually than long fiber thermoplastic (LFT). In this study, tensile, flexural, and impact test of different array types of glass fiber (GF)/thermoplastic composites were performed to compare with GF array. Impregnation property between GF mat and thermoplastic was determined using computed tomography (CT). At CFT method, thermoplastic film is not wet into GF roving and many voids are appeared into composite. This phenomenon affects to decrease mechanical properties. Plain pattern GF mat was the best mechanical and impregnation properties that distance between two roving was set closely to $100{\mu}m$.

• Journal of the Korea Institute of Building Construction
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• v.21 no.4
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• pp.281-291
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• 2021

To reduce the environmental load of the construction industry, there is a need to minimize construction and demolition by strengthening the eco-friendliness of building materials and extending the durable lifespan. Therefore, while many Hanok roof finishing methods have been proposed to address these problems, the current trend is to use the existing method due to issues such as economic feasibility, weight, and durability. The manufacturing method of clay roof tiles used as roofing materials for Hanok buildings is optimized by using a mixture of 64.5% Gyeongju clay, 15.0% kaolin, 15.0% FNS(Ferro Nickel Slag), and 5.5% MAS(Magnesia Aluminum Silicate) under optimal conditions. The results of the experiment involving firing at 1,125℃ showed that flexural strength of 12,102N, which is higher than the standard of KS F 3510, an absorption rate of 6.08%, a volume specific gravity of 2.15g/cm³, and the freeze-thaw properties were satisfied. A method for securing stable quality was studied.

• Journal of Technologic Dentistry
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• v.42 no.4
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• pp.348-354
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• 2020

Purpose: Zirconia is differentiated from other ceramics because of its high resistance to corrosion and wear, excellent flexural strength (900~1400 MPa), and high hardness. Dental zirconia with proven mechanical/biological stability is suitable for the manufacture of implants. However, there are limited in vivo studies evaluating stress distribution in zirconia compared with that in titanium implants and studies analyzing finite elements. This study was conducted to evaluate the stress distribution of the supporting bone surrounding zirconia and titanium implants using the finite element analysis method. Methods: For finite element analysis, a single implant-supported restoration was designed. Using a universal analysis program, eight occlusal points were set in the direction of the occlusal long axis. The occlusal load was simulated at 700 N. Results: The zirconia implant (47.7 MPa) von Mises stress decreased by 5.3% in the upper cortical bone compared with the titanium implant (50.2 MPa) von Mises stress. Similarly, the zirconia implant (20.8 MPa) von Mises stress decreased by almost 4% in the cancellous bone compared with the titanium implant (21.7 MPa) von Mises stress. The principal stress in the cortical and cancellous bone exhibited a similar propensity to von Mises stress. Conclusion: In the supporting bone, the zirconia implant is able to reduce bone resorption caused by mechanically transferred stress. It is believed that the zirconia implant can be a potential substitute for the titanium implant by reinforcing aesthetic characteristics and improving stress distribution.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.33 no.12
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• pp.19-27
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• 2017

This paper is a study to improve the fire-resistance capacity of reinforced concrete (RC) members strengthened by fiber-reinforced-polymer (FRP). The fire resistance of the RC members strengthened by FRP was evaluated through high temperature exposure test. In order to improve the fire resistance of the FRP reinforcing method, a fire-proof board was attached to the reinforced FRP surface and then the high temperature exposure test was carried out to evaluate the improvement of the fire resistance performance. It was confirmed that the resistance to high temperature of NSMR could be improved somewhat compared with that of EBR from the experiment that exposed to high temperature under the load corresponding to 40% of nominal strength. When 30 mm thick fire-resistance (FR) board is attached to the FRP surface, the surface of the reinforced FRP does not reach $65^{\circ}C$, which is the glass transition temperature (GTT) of the epoxy until the external temperature reaches $480^{\circ}C$. In particular, when a high performance fire-proof mortar was first applied prior to FR board attachment, the FRP portion did not reach the epoxy glass transition temperature until the external temperature reached $600^{\circ}C$.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.4
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• pp.25-33
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• 2018

In regard to modular systems, new methods, as well as middle and high-story unit design ideas, are currently being studied. These studies need to focus on the enhanced stiffness and seismic performance of these connections, and see that the development of fully restrained moment connections can improve the seismic performance. For this reason, this study evaluates the performance of the connections of the ceiling bracket-typed modular system through repeated loading tests and analyses. In order to compare them with these modular units, new unit specimens with the bracket connection being different from that of the traditional modular unit specimens were designed, and the results of repeated loading tests were analyzed. In the traditional units, the structural performances of both welding connection and bolt connection were evaluated. In regard to the testing results, the initial stiffness of the hysteresis curve was compared with the theoretical initial stiffness, and the features of all specimens were also analyzed with regard to the maximum moment. In addition, the test results were examined with regard to the connection flexural strength of the steel special moment frame specified under the construction criteria KBC2016. The connections, which were proposed in the test results, were found to be fully restrained moment connections for designing strong column-weak beams and meeting the requirements of seismic performance of special moment frames.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.6
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• pp.271-276
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• 2020

In this study, an amorphous SiC block was manufactured using polycarbosilane (PCS), an organosilicon polymer. The dense SiC blocks were easily fabricated in various shapes via pyrolysis at 1100℃, 1200℃, 1300℃, 1400℃ after manufacturing a PCS molded body using cured PCS powder. Physical and chemical properties were analyzed using a thermogravimetric analyzer (TGA), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and universal testing machine (UTM). The prepared SiC block was decomposed into SiO and CO gas as the temperature increased, and β-SiC crystal grains were grown in an amorphous structure. In addition, the density and flexural strength were the highest at 1.9038 g/㎤ and 6.189 MPa of SiC prepared at 1100℃. The manufactured amorphous silicon carbide block is expected to be applicable to other fields, such as the previously reported microwave assisted heating element.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.5
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• pp.1-8
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• 2020

This study presents a shear strength estimation model, in which the shear failure of a reinforced concrete (RC) member is assumed to be governed by the flexure-shear mechanism. Two shear demand curves and corresponding potential capacity curves for cracked tension and uncracked compression zones are derived, for which the bond mechanism developed between reinforcing bars and surrounding concrete is considered in flexural analysis. The shear crack concentration factor is also addressed to consider the so-called size effect induced in large RC members. In addition,unlike exising methods, a new formulation was addressed to consider the interaction between the shear contributions of concrete and stirrup. To verify the proposed method, an extensive shear database was established, and it appeared that the proposed method can capture the shear strengths of the collected test specimens regardless of their material properties, geometrical features, presence of stirrups, and bond characteristics.