• Earthquakes and Structures
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• v.12 no.2
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• pp.237-250
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• 2017

There has been increasing attention in many countries on seismic retrofit of old fashioned RC structures in recent years. In such buildings, the joints lack transverse reinforcement and suffer inadequate seismic dimensional requirements and the reinforcement is plain bar. The behavior of the joints is governed by sliding of steel bars and diagonal shear failure is less influential. Different methods to retrofit beam-column joints have been proposed in the literature such as wrapping the joint by FRP sheets, enlargement of the beam-column joint, and strengthening the joint by steel sheets. In this study, an enlargement technique that uses external prestressed cross ties with steel angles is examined. The technique has already been used for substructures reinforced by deformed bars and has advantages such as efficient enhancement of seismic capacity and lack of damage to the joint. Three reference specimens and two retrofitted units are tested under increasing lateral cyclic load in combination with two levels of axial load. The reference specimens showed relatively low shear strength of 0.150${\surd}$($f_c$) and 0.30${\surd}$($f_c$) for the exterior and interior joints, respectively. In addition, relatively brittle behavior was observed and large deformations extended into the panel zone of the joints. The retrofit method has increased ductility ratio of the interior beam-column joints by 63%, and energy dissipation capacity by 77%, relative to the control specimen; For external joints, these values were 11%, and 94%. The retrofit method has successfully relocated the plastic joints far from the column face. The retrofit method has improved shear strength of the joints by less than 10%.

• Journal of The Korean Society of Agricultural Engineers
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• v.50 no.2
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• pp.19-26
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• 2008

This study has been carried out to investigate the dynamic characteristics of RC slabs. For this purpose, the 20-node solid element has been used to discretize the RC slabs into two parts of concrete and rebar. The material non-linearity considering elasto-visco plastic model and the smeared crack model have been adopted in the finite element formulation. The applied load can handle step load, load intensity of harmonic load, area of distributed load and frequency. The frequency of harmonic load has an significant effect on dynamic behaviour in terms of displacement. As the frequency is increased, the effect of load amplitude is more serious. Especially, if the frequency of harmonic load exceeds 30 Hz, it is noted that the displacement by harmonic load is greater than that by step load. In case of harmonic load, the damping effect shows no certain tendency with respect to frequency of load. In details, the damping is effective when the frequency of harmonic load is 2 Hz, but there is no consistent tendency according to damping ratio. The dynamic response when the frequency of harmonic load is 3 Hz shows same result for undamped case as well as for damped case with 5% damping ratio. It is also noted that we can get the largest deflection for damped case with 1% damping ratio. However, there is not any damping effect when the frequency of harmonic load is greater than 4 Hz.

• Journal of the Korean Society for Advanced Composite Structures
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• v.5 no.1
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• pp.1-8
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• 2014

Pultruded glass fiber reinforced polymeric plastic (PFRP) and FRP member manufactured by sheet molding compound (SMC) have superior mechanical and physical properties compared with those of conventional structural materials. Since FRP has an excellent corrosion-resistance and high specific strength and stiffness, the FRP material may be highly appreciated for the development of floating-type photovoltaic (PV) power generation system. In this paper, advanced floating PV generation system made of PFRP and SMC is designed. In the design, it includes tracking solar altitude by tilting photovoltaic arrays and tracking solar azimuth by spinning structures. Moreover, the results of the finite element analysis (FEA) are presented to confirm stability of entire structure under the external loads. Additionally, installation procedure and mooring systems in the Hap-Cheon Dam are discussed and the measurement of strain under the actual circumstances is conducted for assuring stability of actually installed structures. Finally, by comparison with allowable stress, appropriate safety of structure is confirmed to operate the system.

• Journal of Korean Society of Steel Construction
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• v.12 no.1 s.44
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• pp.55-63
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• 2000

This paper is a study on the behavior of Concrete-Filled Square Tubular(CFST) column to H-beam connections reinforced with external stiffeners and reinforcing bar. The cyclic loading tests of 5 test specimens were carried out. The main Parameters are as follows; 1)the length of the stiffener: 200mm, 250mm, 2)the diameter of reinforcing bar: HD16, 19. The results of the researches demonstrate that the increase of the stiffener length was more effective than the increase of the area of reinforcing bar in the point of both strength and stiffness. By reinforcing external stiffeners, stable hysteretic behavior was shown and plastic hinge was formed on the beam flange. Cold-formed tube sections should be used carefully to avoid the welding fracture at the round corners of section, and the proposed welding methods are suitable for this connections.

• Journal of Korean Society of Steel Construction
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• v.13 no.5
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• pp.503-511
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• 2001

Structures are designed against earthquakes and reinforced concrete shear walls or steel bracings are usually used as aseismic resistant element. However their hysteretic characteristics in plastic region ductility and capacity of energy absorption are not always good. Besides their stiffness is so rigid that structure designed by static analysis is occasionally disadvantageous. when dynamically analized. Generally a steel plate subjected to shear force has a good deformation capacity Also it has been considered to retain comparative shear strength and stiffness Steel shear wall can be used as lateral load resistant element for seismic design. However there was little knowledge concerning shear force-deformation characteristics of steel plates up to their collapse state In this study a series of shear loading tests of steel plate collapse state. In this study a series of shear loading tests of steel plate surrounded by vertical and horizontal ribs were conducted with the parameters of D/H ratios rib type and the loading patterns. The test result is discussed and analyzed to obtain several restoring characteristics. that is shear force-deformation stiffness and yield strength etc.

• Journal of Environmental Science International
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• v.18 no.12
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• pp.1339-1347
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• 2009

This study tried to investigate and analyze the actual state such as the regional, classified, and material characteristics of the water quality in order to research the several factors by which the filtrated water of the total 250 cases can be polluted in the water tank. The 215 points (86%) clean the water tanks twice a year regularly and J-city has done the best job of cleaning the water tanks. The fifty points (20%) of the total 250 investigation points examine the water quality of the water tanks every year, however, the 175 investigation points (70%) do not execute the inspection of water quality. In the case of the regional characteristics in the water quality, the 23 points (46%) in H-county, the 17 points (34%) in S-county, and the 16 points (32%) in G-city are incongruent in the standard, and the incongruity ratio of the water quality in J-city is the lowest. The result of the classified incongruity shows that total coliforms were found at the 61 investigation points, mesophilic bacteria were found at the 27 points, and turbidity was found at the 12 points. In the case of the material incongruity, concrete was found at the 63 investigation points as the most distinguished factor, and FRP (fiberglass reinforced plastic) at the 23 points, SMC (sheet molding compound) at the 12 points, and stainless steel was found at the 2 points.

• Carbon letters
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• v.16 no.3
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• pp.147-170
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• 2015

In recent decades, there has been an increasing interest in the use of carbon fiber reinforced plastic (CFRP) in aerospace, renewable energy and other industries, due to its low weight and relatively good mechanical properties compared with traditional metals. However, due to the high cost of petroleum-based precursors and their associated processing costs, CF remains a specialty product and as such has been limited to use in high-end aerospace, sporting goods, automotive, and specialist industrial applications. The high cost of CF is a problem in various applications and the use of CFRP has been impeded by the high cost of CF in various applications. This paper presents an overview of research related to the fabrication of low cost CF using polyethylene (PE) control technology, and identifies areas requiring additional research and development. It critically reviews the results of cross-linked PE control technology studies, and the development of promising control technologies, including acid, peroxide, radiation and silane cross-linking methods.

• Journal of the Korea Concrete Institute
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• v.15 no.6
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• pp.877-887
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• 2003

For a performance-based design of structural walls, it is necessary to develop a rational design method for determining the length and detail of boundary confinement so as to satisfy the given ductility demand. In the present study, the curvature capacity of a structural wall with boundary confinement was estimated considering the effects of various design parameters. The curvature demand of the plastic hinge corresponding to the given design displacement was also determined. By equalizing the curvature capacity to the demand, a design method for determining the length of boundary confinement, was developed. According to the design method, the length of boundary confinement increases as axial compressive load and design displacement increase, and as concrete strength, wall thickness, amount of lateral reinforcement and aspect ratio decrease. A study was performed on details for effective lateral confinement of walls with rectangular cross-section. Based on the findings, design guidelines on spacings of ties and cross-ties were proposed.

• 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.

• Journal of the Korea Convergence Society
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• v.9 no.5
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• pp.151-156
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• 2018

In this study, CFRP and metal or nonmetal were bonded with adhesive and the fracture study on this material was carried out. CFRP at the upper side of specimen and metal or nonmetal were assigned at the lower side of specimen by using DCB specimen as the analysis condition. And it was desribed that the structural adhesive were bonded between both upper and lower sides. As this analysis result, the least equivalent stress was shown at the specimen bonded with aluminium. The maximum shear stress was shown to become lowest at the de-bonded CFRP specimen when titanium was used. In conclusion, it was shown that the deformation of specimen became lowest when titanium was used. On the basis of this study result, the esthetic sense can be shown as the fracture data of bonded interface using adhesive are grafted onto the real life.