• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.3
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• pp.271-278
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• 2019

The corrosion of reinforcements embedded in concrete causes severe deterioration in reinforced concrete structures. As a countermeasure, epoxy coated reinforcements are used to prevent corrosion of reinforcements. When epoxy coated bars are used, the resistance of corrosion is excellent, but epoxy coating on the bars have a disadvantage of reduction in bond capacity comparing to that of normal bars. Therefore, it is necessary to confirm the bond performance of epoxy coated reinforcements through experimental and analytical methods. Bond behaviors of epoxy coated bars for various diameters of 13 and 19mm and thicknesses of cover concrete of 3 types(ratio of cover to bar diameter) are examined. As the diameters of the epoxy coated bars increase, the difference of bond strength between epoxy coated and uncoated bars also increases and damage patterns showed pull out failure. In addition, finite element analysis was performed based on the bond-slip relationship obtained by direct pullout test and compared with the flexural test results. It is considered that flexural member test is more useful than pullout test for simulating the behavior of actual structure.

• Tunnel and Underground Space
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• v.32 no.6
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• pp.568-585
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• 2022

In the present study, we proposed a numerical method for simulating thermally induced fracture slip using a grain-based distinct element model (GBDEM). As a part of DECOVALEX-2023, the thermo-mechanical loading test on a saw-cut rock fracture conducted at the Korea Institute of Civil Engineering and Building Technology was simulated. In the numerical model, the rock sample including a saw-cut fracture was represented as a group of random Voronoi polyhedra. Then, the coupled thermo-mechanical behavior of grains and their interfaces was calculated using 3DEC. The key concerns focused on the temperature evolution, thermally induced principal stress increment, and fracture normal and shear displacements under thermo-mechanical loading. The comparisons between laboratory experimental results and the numerical results revealed that the numerical model reasonably captured the heat transfer and heat loss characteristics of the rock specimen, the horizontal stress increment due to constrained displacement, and the progressive shear failure of the fracture. However, the onset of the fracture slip and the magnitudes of stress increment and fracture displacement showed discrepancies between the numerical and experimental results. We expect the numerical model to be enhanced by continuing collaboration and interaction with other research teams of DECOVALEX-2023 Task G and validated in further study.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.101-113
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• 2013

This paper intends to develop mechanical analysis models that are able to predict complete nonlinear behavior in the bolted connector subjected to cyclic loads. In addition, experimental data which were obtained from loading tests performed on the T-stub connections are utilized to validate the accuracy of analytical prediction and the adequacy of numerical modeling. The behavior of connection components including tension bolt uplift, bending of the T-stub flange, stem elongation, relative slip deformation, and bolt bearing are simulated by the multi-linear stiffness models obtained from the observation of their individual force-deformation mechanisms in the connection. The component springs, which involve the stiffness properties, are implemented into the simplified joint element in order to numerically generate the behavior of full-scale connections with considerable accuracy. The analytical model predictions are evaluated against the experimental tests in terms of stiffness, strength, and deformation. Finally, it can be concluded that the mechanical models proposed in this study have the satisfactory potential to estimate stiffness response and strength capacity at failure.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.1
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• pp.43-53
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• 2011

For reinforced concrete members, the bond strength is one of the important factors between two materials: concrete and reinforcing element. This study concerns the bond strength of deformed bars in artificial lightweight aggregate concrete by pull-out test. 144 cubic specimens were manufactured for the test. concrete compressive strength, size of deformed bar and embedment lengths were considered as variables in this study. Normal concrete with W/C ratio 50% specimens were tested for the comparison. Test results included the bond stress-slip responses and modes of failure. Bond strength increased with an increase of compressive strength of concrete according to W/C ratio. The equation of bond stress of polymer-modified lightweight aggregate concrete were proposed by regression analysis based on the result.

• Journal of the Korea Concrete Institute
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• v.24 no.1
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• pp.79-86
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• 2012

Though steel reinforcing bars are the most widely used tensile reinforcement, corrosion problems are encountered due to the exposure to aggressive environments. As an alternative material to steel, the fiber reinforced polymers have been used as reinforcement in concrete structures. However, bond strength of FRP rebar is relatively low compared to steel rebar. It has been reported that fibers in matrix can resist crack growth, propagation and finally result in an increase of toughness. In this study, high-strength concrete reinforced with structural fibers was produced to enhance interfacial bond behavior between FRP rebar and concrete matrix. The interfacial bond-behaviors were investigated from a direct pullout test. The test variables were surface conditions of GFRP bars and fiber types. Total of 54 pullout specimens with three different types of bars were cast for bond strength tests. The bond strength-slip responses and resistance of the bond failure were evaluated. The test results showed that the bond strength and toughness increased according to the increased fiber volume.

• Journal of Korean Society of Steel Construction
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• v.16 no.4 s.71
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• pp.425-432
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• 2004

Large studs were suggested not only for the design of steel-concrete composite bridges with simplified sections but also for the shear connection in precast decks requiring uniform distribution of shear pockets. Based on the push-out test results on studs with diameters of more than 25 mm, partial composite beams with 40%-degree shear connection were fabricated, and static tests were performed. The ultimate strength and horizontal shear load redistribution of partial composite beams, which have parameters of stud shank diameters and distribution, were evaluated, and group failure in the shear span was observed. Since the flexural strength of composite beams are dependent on the strength of their shear connection, the strength of the stud connection was estimated and it showed considerably higher shear strength. From the load-slip curves, the sufficient ductility and load redistribution of large studs were confirmed. Uniformly distributed large studs can provide proper ultimate behavior of composite beams.

• Journal of Chest Surgery
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• v.28 no.6
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• pp.533-541
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• 1995

We recently developed a new model of moving actuator type totally implantable artificial heart[TIAH , based on the reverse position of the aortic and pulmonary conduits. This concept was proposed by one of surgeons in our team[Joon-Ryang Rho, M.D. to facilitate anatomical fitting of TIAHs. The moving actuator type electromechanical TIAH consisted of the left and right blood sacs, and the moving actuator including a motor. The inverted umbrella type polyurethane valves were used in the blood pumps. The aortic conduit was positioned anterior to the pulmonary conduit, which was the opposite relation to the conventional configuration of other total artificial hearts. We also adapted slip-in connectors for the aortic and pulmonary conduits. Two sheep , weighing 60-69 kg, were used for implantation. After small cervical incision and trans-sternal bilateral thoracotomy, cardiopulmonary bypass [CPB was administered using an American Optical 5-head pump and a membrane oxygenator[Univox-IC, Bentley . The anterior and posterior vena cavae were drained separately for venous return. An arterial return cannula was inserted into the right common carotid artery. During CPB, almost all of the ventricular myocardium was excised down to the atrioventricular groove and the artificial heart was implanted. We achieved 3-day survival in the first sheep and 2-day survival in the second. The day after operation the first sheep was successfully extubated and the second sheep was weaned from a respirator with good condition. After extubation, the first sheep walked around in the cage and fed herself. Serial laboratory and hemodynamic examinations were done during the experiments. In both sheep, pulmonary dysfunction was gradually developed, which was accompanied by acute renal failure. The animals were sacrificed and autopsy was done. Unexpected pregnnacy was incidentally found in both sheep. To our knowledge this is the first report of significant survival cases in the orthotopic implantation of electric TIAH using sheep.

• Journal of the Korea Concrete Institute
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• v.28 no.2
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• pp.235-244
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• 2016

This study was conducted to verify seismic performance of special moment frame's joints at roof-level with high-strength concrete and SD600 bars. K-RC-H was designed according to the seismic code and K-HPFRC-H had 150% of the original hoop spacing and 1.0% steel fiber volume fraction compared with K-RC-H. Both specimens had remarkable seismic performance without noticeable decrease in moment, but with very good energy dissipation before rebar failure. The U-bars in the joint sufficiently constrained rebar's action that pushed the cover upward. SD600 bars with $1.25l_{dt}$ had minimum slip in the joint. It was considered that the steel fiber contributed to improvement of the bending moment and joint shear distortion, and the result showed that it would be possible to increase the hoop spacing to 150% of the regular spacing.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.185-188
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• 2008

Flat plate system has structural weakness such as punching shear. Punching shear resistance can be increase by using a lager column section and effective depth, higer concrete compressive strength, and more flexural reinforcement ratio. But using a shear reinforcement is most economical, enable, workable solution in flat plate. The slab with thickness smaller than 250mm can not perform effectively due to insufficient development length of shear reinforcement in the slab. In case of proposed reinforcements, since the shear reinforcements were installed between the top bar and the bottom bar, shear elements generated slip failure before they reached yield. strength. effect of anchorage strength were effective anchorage length, concrete strength, diameter of shear element and anchorage detail. considering effect of slab thickness and concrete strength, formula of K factor propose in thin flat plate slab. by considering effect of anchorage length and concrete strength, strength of shear reinforcement will be computed correctly in thin flat plate slab.

• Journal of the Korean Geotechnical Society
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• v.19 no.1
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• pp.41-49
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• 2003

Rainfall-induced landslides in a weathered granite soil slope usually happen on shallow slip surfaces above the groundwater table. The pore-water pressure of soil above the groundwater table is usually negative. This negative pore-water pressure (or matric suction) has been found to make a large contribution to the slope stability. Therefore, the variation of in-situ matric suction profiles with time elapse in a soil slope should be understood. In this study, a field measurement program was carried out from June to August, 2001 in order to monitor in-situ matric suctions and volumetric water contents in a weathered granite soil slope. Finite-element transient seepage analyses are also conducted using SEEP/W. The influence of climatic conditions on the variation of in-situ matric suctions could be found to decrease rapidly with the change of depth. It could be found that decrement of matric suction induced by precipitation is affected not only by the amount and duration of rainfalls but also by the initial matric suction just prior to rainstorms. The soil-water characteristic from the field monitoring tends toward the wetting path of SWCC obtained from the laboratory test.