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Now showing items 1 - 16 of 29

  • Numerical Simulations of Local Scour at Samsan Bridge Piers in Korea

    Lee, Jooyong   Park, Sun-Kyu   Hong, Sungnam  

    The Samsan Bridge connects Ganghwa Island and Incheon in the mid-western region of South Korea. The country is making an effort to improve access to the island from its major cities, and the construction of the bridge is part of that process. External factors such as wind waves, tide currents, currents, and scour depths around piers should be considered in the construction of a bridge. In order to obtain scour depth values around bridge piers, this study conducted numerical simulations on morphological changes using the SADEM (SAnd Deposit and Erosion Model). The morphological changes were calculated by solving the conservation of sediment transport equation. A field measurement was performed at the Seokmo channel in the Han River estuary (South Korea) to verify the numerical results. A 153x210 grid system with a coarse grid size of 22.8 x 30 km was used in the SADEM. The maximum stream velocities of 10, 50, and 100-year flood return periods during the ebb tide contributes to sediment mobilization in the Seokmo channel. The maximum scour depth was calculated to be 9 m around the central bridges pier during the flood ebb for the 100-year return period. This was due to the upstream discharge during river flooding. The results of the numerical simulations are expected to be objective indicators of optimal design, construction, and future maintenance of the Samsan Bridge.
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  • Optimal mix and freeze-thaw durability of polysulfide polymer concrete

    Hong, Sungnam   Kim, Hyeonjun   Park, Sun-Kyu  

    A study was conducted to determine the optimal mix design for polysulfide polymer concrete (PPC). Two stage binder tests and polymer concrete mixing tests were carried out for this purpose. The optimal mixing ratio was determined from the test results. In addition, the strength and freeze-thaw resistance of specimens produced using the optimal mixing ratio were evaluated. The results of the strength tests showed that the specimens satisfied the strength requirements of the relevant design codes. Repeated freezing and thawing significantly decreased the mechanical strength of the specimens but had an insignificant effect on the specimens' relative dynamic modulus of elasticity (RDME). It was found that more than 300 freeze-thaw cycles could cause a problem for PPC in terms of its strength. (C) 2016 Elsevier Ltd. All rights reserved.
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  • Behavior of Concrete Beams with Peel-Plied Aramid-Fiber-Reinforced Polymer Plates

    Hong, Sungnam   Park, Sun-Kyu  

    The effect of fiber-reinforced polymer (FRP) plates, to which a peel-ply was fastened to increase their bonding area, on the behavior of strengthened concrete beams was investigated. A total of six concrete beams were tested. For the FRP plates, aramid-fiber-reinforced polymer (AFRP) ones were used. The test variables included their surface treatment (smooth and deformed), the depth of removal of concrete cover (0 and 10 mm), and the number of the plates. Each beam was tested in four-point bending under displacement control up to failure. Based on the experimental results obtained, the effect of the peel-plied AFRP plates on the flexural behavior of the concrete beams was evaluated.
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  • Effect of vehicle-induced vibrations on early-age concrete during bridge widening

    Hong, Sungnam   Park, Sun-Kyu  

    The purpose of this study was to conduct laboratory experiments that considered the effect of vehicle-induced vibrations on fresh concrete to determine the attainable concrete strength for bridge widening. A laboratory experimental program was carried out, where 120 concrete specimens were used in total to measure the compressive and bond strengths. The experiment results showed that vehicle-induced vibration does not need to be considered a serious risk to the concrete strength if the vibration duration is 6 h or less and the peak particle velocity is 0.3 cm/s or less. (C) 2014 Elsevier Ltd. All rights reserved.
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  • Behavior of Concrete Columns Repaired with Polymer Mortar and Epoxy Fiber Panel

    Hong, Sungnam   Park, Sun-Kyu  

    Underwater structures are not easy to check for the degree of damage or to repair and strengthen damaged regions. Even during repair and strengthening, quality control is very difficult, because the work is done under water. Moreover, underwater structures severely deteriorate, owing to special environmental conditions. If this deterioration continues, the structures face serious structural problems, because of the corrosion of steel rods and the loss of concrete sections. Repairing or strengthening underwater structures requires effective, economic underwater repair and reinforcement techniques that allow the same working conditions as on the ground while maintaining dry condition for the repair sections. However, systematic studies on the repair and strengthening techniques for underwater structures are insufficient. This study proposes a new repair method for underwater structures, which applies epoxy fiber panel forms and shear connectors. To demonstrate the repair effects, this study compared and evaluated the failure modes and repair effects by the surface condition of repair sections, by applying various repair methods, in consideration of the ground and underwater conditions.
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    The present invention relates to a weight balancer (100) and a pipe joining method that is capable of reducing a load of pipes when arranging and welding the pipes in ships, plants, piping work sites and the like. A weight balancer (100) according to the present invention includes an operation plate (180) for putting an alignment object; a plurality of load cells (145,146) installed in the lower portion of the operation plate (180); a controller (120) which receives a detection signal generated from the load cell (145,146) and analyses the information of the alignment object to generate a control signal; an operation force driver (130) which receives the control signal from the controller (120) to control an operational pressure of each of a plurality of pressure supply lines; and a plurality of leveling cylinders (150) and balancing devices (160) which are connected to the pressure supply lines to control a location or pose of the operation plate (180) so as to correspond to the size of the operational pressure controlled by the operation force driver (130).
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  • Antioxidant effect of human placenta hydrolysate against oxidative stress on muscle atrophy

    Bak, Dong-ho   Na, Jungtae   Im, Song I.   Oh, Chang Taek   Kim, Jeom-Yong   Park, Sun-Kyu   Han, Hae Jung   Seok, Joon   Choi, Sun Young   Ko, Eun Jung   Mun, Seog-Kyun   Ahn, Suk-Won   Kim, Beom Joon  

    Sarcopenia, which refers to the muscle loss that accompanies aging, is a complex neuromuscular disorder with a clinically high prevalence and mortality. Despite many efforts to protect against muscle weakness and muscle atrophy, the incidence of sarcopenia and its related permanent disabilities continue to increase. In this study, we found that treatment with human placental hydrolysate (hPH) significantly increased the viability (approximately 15%) of H2O2-stimulated C2C12 cells. Additionally, while H2O2-stimulated cells showed irregular morphology, hPH treatment restored their morphology to that of cells cultured under normal conditions. We further showed that hPH treatment effectively inhibited H2O2-induced cell death. Reactive oxygen species (ROS) generation and Mstn expression induced by oxidative stress are closely associated with muscular dysfunction followed by atrophy. Exposure of C2C12 cells to H2O2 induced abundant production of intracellular ROS, mitochondrial superoxide, and mitochondrial dysfunction as well as myostatin expression via nuclear factor-kappa B (NF-kappa B) signaling; these effects were attenuated by hPH. Additionally, hPH decreased mitochondria fission-related gene expression (Drp1 and BNIP3) and increased mitochondria biogenesis via the Sirt1/AMPK/PGC-1 alpha pathway and autophagy regulation. In vivo studies revealed that hPH-mediated prevention of atrophy was achieved predominantly through regulation of myostatin and PGC-1 alpha expression and autophagy. Taken together, our findings indicate that hPH is potentially protective against muscle atrophy and oxidative cell death.
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  • Thermal degradation of anisotropic conductive film joints under temperature fluctuation

    Kim, Jong-Woong   Koo, Ja-Myeong   Lee, Chang-Yong   Noh, Bo-In   Yoon, Jeong-Won   Kim, Dae-Gon   Park, Sun-Kyu   Jung, Seung-Boo  

    Thermo-mechanical reliability of the anisotropic conductive film (ACF) joints in relation with flip chip bonding forces was evaluated by thermal shock testing. Two kinds of main failure modes were detected after thermal shock testing: formation of a conduction gap between conductive particles and Au bump or Ni/Au-plated Cu pad, and delamination of the adhesive matrix from the plated Cu pad on the flexible substrate. The determination of the failure mode was mainly affected by the variation of the bonding force. The main failure mode of the thermally shocked ACF joints was conduction gap for the joints with low bonding forces and adhesive matrix delamination for the joints with high bonding forces. Finite element analysis was also performed to determine the stress distributions within the two kinds of flip chip packages having different bonding gaps when it was stressed by the temperature rising. (C) 2007 Elsevier Ltd. All rights reserved.
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  • New Priority Ranking Algorithm for the Deteriorated Coastal Bridges Considering Network Level

    Park, Jongho   Park, Sun-Kyu   Choi, Jinwoong   Hong, Sungnam  

    Bridges are currently constructed and designed considering the structural safety required by the design code. However, coastal bridges are continuously deteriorated by many causes such as concrete spalling and exfoliation due to aging, faulty construction, and other deterioration factors. In this study, a prior ranking algorithm is investigated for performing maintenance management of coastal bridges and composed of more reasonable algorithm with studied on previous precedence priority ranking algorithm to realize bridge maintenance. With regard to a rating index of a total of 100 points, appearance defect index and load capacity deficiency was suggested with 40 and 60 point respectively. It is a more reasonable prior ranking algorithm that reflects the load capacity function, traffic of bridges and deteriorated bridge with high degree of deficiency point.
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  • Stress-strain and deflection relationships of RC beam bonded with FRPs under sustained load

    Kim, Sung-Hu   Han, Kyoung-Bong   Kim, Kwang-Soo   Park, Sun-Kyu  

    Fiber-reinforced polymer (FRP) systems that have a strong resistance against long-term deformation must provide improved serviceability to reinforced concrete (RC) members under sustained loads. Consequently, there is a need to develop a method for accurately predicting the time-dependent behavior of RC beams that are externally bonded with FRPs. However, there are very few previous studies that have been carried out or experimental results available, oil the time-dependent behavior of RC beams externally bonded with FRP. In order to enable a reasonable prediction, correlations should first be clarified between the stress-strain relationship of the concrete, the reinforcement and the FRP that changes over time. By using these correlations, deflections under sustained loads should then be forecast. In this study, RC beams were fabricated for this purpose. Carbon reinforced polymer (CFRP) and glass reinforced polymer (GFRP) materials were bonded to the tension face of the two respective RC beams. The beams were then placed under sustained loads for 300 days. For the specimens that were externally bonded with FRPs and for the conventional specimen, the strain of the compression and tension reinforcement and the strain of FRP and deflection were measured respectively for comparison. In order to theoretically predict the time-dependent behavior of the RC Beam externally bonded with FRPs, creep coefficients for concrete and shrinkage strains were calculated by using the CEB-FIP and the ACI-209 Codes. For the method used to forecast the stress-strain relationships of the concrete, reinforcement and FRPs that change over time were theoretically clarified and were then compared with the experimental results. The deflection of the RC Beams externally bonded with FRP was predicted by using the ACI 318 Standard, EMM, AEMM, Branson's method, and Mayer's method. They were also compared to the experimental results. Subsequently, in the case of RC Beams externally bonded with FRPs under sustained loads, the proposed method proved that it is possible to accurately predict long-term deformations. (C) 2009 Elsevier Ltd. All rights reserved.
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  • Bearing Replacement for Prestressed Concrete I-Girder Bridges

    Park, Sun-Kyu   Kim, Hyeong-Yeol   Kim, Jung-Hyuk  

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  • Estimation of torsional crack width for concrete structural members

    Park, Sun-Kyu   Ko, Won-Jun   Kim, Hyeong-Yeol  

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  • SK-PC-B70M confers anti-oxidant activity and reduces A beta levels in the brain of Tg2576 mice

    Seo, Ji-Seon   Kim, Tae-Kyung   Leem, Yea-Hyun   Lee, Kang-Woo   Park, Sun-Kyu   Baek, In-Sun   Kim, Kyoung-Shim   Im, Guang-Jin   Lee, Soo Min   Park, Yang Hae  

    SK-PC-B70M is an oleanolic-glycoside saponin-enriched fraction derived from the root of Pulsatilla koreana. Recently, it was reported that hederacolchiside-E is an active ingredient of SK-PC-B70M that confers a neuroprotective effect against the cytotoxicity induced by A beta(1-42) in SK-N-SH neuroblastoma cells. SK-PC-B70M improves scopolamine-induced impairments of spatial working memory in rats. In the present study, we investigated whether SK-PC-B70M has a beneficial effect on the Tg2576 murine model of Alzheimer's disease. ELISA analysis revealed that the levels of soluble and insoluble forms of A beta(1-42) in Tg2576 mice fed SK-PC-B70M (2000 ppm) from 11 months to 16 months of age were reduced to, respectively, 66% and 79% of the control Tg2576 mice. Anti-A beta antibody-stained brain sections of Tg2576 mice with SK-PC-B70M (2000 ppm) consistently showed a reduction in plaque formation in the brain. Western blot analyses showed altered expressions of various cellular factors, such as up-regulation of transthyretin, phospho-ERK, and phospho-CREB in the brain treated with SK-PC-B70M. SK-PC-B70M suppressed the neuronal toxicity induced by H2O2 in primary cortical culture. Moreover, biochemical and immunohistochemical analyses showed that the levels of malondialdehyde (MDA) and 4-hydroxy-2-nonenal (HNE), oxidized by-products of lipid peroxidation, were notably reduced in the hippocampus of Tg2576 mice treated with SK-PC-B70M compared with the Tg2576 control. These results suggest that SK-PC-B70M attenuates AD-like pathology in the brain of Tg2576 mice. (C) 2009 Elsevier B.V. All rights reserved.
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  • Flexural behaviour of reinforced concrete beams strengthened with prestressed carbon composites

    Yang, Dong-Suk   Park, Sun-Kyu   Neale, Kenneth W.  

    In this study, a total of 13 FRP-strengthened reinforced concrete beams were tested in flexure and analyzed using the finite element method. The various variables included bonding or no bonding of the FRP, the anchorage system, the amount of prestressing, and the span length. The experiments consisted of one control beam, two non-prestressed FRP-bonded beams, four prestressed FRP-unbonded beams, four prestressed FRP-bonded beams, and two prestressed FRP-unbonded beams with different span lengths. All the beams were subjected to three-point and four-point bending tests under deflection control, with the loading, deflection and failure modes recorded to the point of failure. A nonlinear finite element analysis of the tested beams was also performed using the DIANA software; this analysis accounted for the nonlinear concrete material behaviour, the reinforcement, and an interfacial bond-slip model between the concrete and CFRP plates. The aim of this investigation was to study the flexural performance of reinforced concrete members strengthened using CFRP plates, employing different FRP bonding and prestressing methods. The failure mode of the prestressed CFRP-plated beams was not debonding, but FRP rupture. For the reinforced concrete members strengthened with externally bonded prestressed CFRP plates, debonding of the composite laminates occurred in two stages. After the debonding of the CFRP plates that occurred in the bonded cases, the behaviour of the bonded CFRP-plated beams changed to that of the unbonded CFRP-plated beams due to the effect of the anchorage system. The flexural test results and analytical predictions for the CFRP-strengthened beams were compared and showed very good agreement in terms of the debonding load, yield load, and ultimate load. The ductility of the beams strengthened with CFRP plates having the anchorage system was considered high if the ductility index was above 3. (C) 2008 Elsevier Ltd. All rights reserved.
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  • An Experimental and Analytical Study on the Deflection Behavior of Precast Concrete Beams with Joints

    Park, Jongho   Choi, Jinwoong   Jang, Yongjoon   Park, Sun-Kyu   Hong, Sungnam  

    The use of precast concrete modular construction in the replacement and rebuilding of old structures has recently increased. However, the joints between modules in this type of construction exhibit special behavior that should be considered when analyzing the behavior of modular members. Both stability and serviceability should be studied; however, existing research has only addressed the former. Research regarding serviceability, involving deflection and crack development and propagation, is lacking. This study considers the difference in strength between on-site cast and precast segmental concrete to accurately evaluate the deflection of precast concrete flexural members with joints within the lapped splice. In addition, to reflect an initial crack, the deflection is calculated and evaluated by reflecting the effect of tension-stiffening and subsequently redefining the attached transmission lengths of the left and right sides of the cracked surface as a new cracked region. As a result of explicitly including joint behavior which is considered attached transmission length and characteristic by concrete strength, a more accurate calculation of deflection is developed.
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  • A Study on the Design of the Top Flange of a Modular T-Girder Bridge Using the Limit State Design Method

    Park, Jongho   Choi, Jinwoong   Lee, Hongmyung   Park, Sun-Kyu   Hong, Sungnam  

    This study involved applying a design code change on a modular bridge design. The top flange of a modular T-girder bridge was examined by the Korean Highway Bridge Design Code Limit State Design (2015) and was compared with the Korean Highway Bridge Design Code (2010) in terms of the stability under the bending moment. In addition, the cross-sectional height and reinforcement amount were re-designed to obtain a safety factor similar to the original code. The reinforcement arrangement and development of the transverse joints were examined in the section considered. The result indicated that the application of the Korean Highway Bridge Design Code Limit State Design (2015) increased the bending moment safety factor and decreased the width of the transverse joints. The results of the re-design with respect to a safety factor similar to that in the Korean Highway Bridge Design Code (2010) indicated that it was possible to reduce the cross-sectional height and reinforcement amount. Furthermore, based on the obtained section, the results revealed that the width of the transverse joints could be reduced by changing the arrangement of lap splices from the straight bar to the loop.
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