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Now showing items 17 - 29 of 29

  • Experimental Investigation on the Application of Ultra-Rapid-Hardening Mortar for Rigid Small Element Pavement

    Han, Eui-Seok   Gong, Junho   Cho, Dooyong   Park, Sun-Kyu  

    Natural stones have been typically used as a paving material in historically conserved areas due to architectural aesthetic aspect and environmental impact. However, they have been traditionally suggested in light traffic volume due to the defects caused by the increased traffic loading and volume. The failures can lead to diverse problems such as losing flatness, severe damage to both vehicles and pedestrians, high traffic congestion, maintenance cost, etc. In order to overcome these obstacles, ultra-rapid-hardening (URH) cement for rigid small element pavement (SEP) was implemented as both jointing and laying course materials. Additionally, their mechanical properties were investigated according to BS 7533-4 and National Stone Surface (NSS) in the UK. Preliminarily, the proper mix mortar design was found by comparing design parameters. The compressive and flexural strength of the joint and laying course by age was verified, and the results in early-age stage were satisfied with the requirements. The adhesive and shear strengths depending upon the width of the joint were determined, and from the test outcomes, the optimal thickness of the joint was found as 15mm. Furthermore, by contrasting the compressive strength of the laying course with the punching shear strength, the shear strength regarding joint states was increased by up to 134.3% (fully restrained), 127.9% (semirestrained), and 107.2% (non restrained). This investigation would be possible to use as baseline data for an evaluation of the long-term performance of rigid SEP.
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  • Service life prediction of repaired concrete structures under chloride environment using finite difference method

    Song, Ha-Won   Shim, Hyun-Bo   Petcherdchoo, Aruz   Park, Sun-Kyu  

    Service life of concrete structures under chloride environment can be predicted by formulations based on the mechanism of chloride ion diffusion. This mechanism can be mathematically described using the partial differential equation (PDE) of the Fick's second law. One-dimensional PDE can be solved analytically by assuming constant surface chloride ion concentration and constant diffusion coefficient. However, the solution becomes more complicated when two additional conditions are included, i.e., concrete cover repair or replacement and time dependent variation of the surface chloride ion concentration and diffusion coefficient. In this paper, a numerical finite difference based formulation is proposed to effectively accommodate these two additional conditions. By virtue of numerical computation, the nonlinear initial chloride ion concentration can be treated in point-wise manner and both the time dependent surface chloride ion concentration and diffusion coefficient can be iteratively updated. Based on a Crank-Nicolson scheme within the finite difference method, a proper formulation accounting for space-dependent diffusion coefficient was derived; chloride ion concentration profiles are obtained and the service life of repaired concrete structures under chloride environment is predicted. Numerical examples and observations are finally presented. (C) 2008 Elsevier Ltd. All rights reserved.
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  • Application of a New Anchorage towards the Flexural Strengthening of RC Rectangular Beams with External Steel Tendons

    Hong, Sungnam   Cho, Dooyong   Park, Sun-Kyu  

    To strengthen concrete beams, a new anchorage was proposed, and its performance was evaluated in this study. Seven concrete beams were manufactured and flexurally loaded with displacement control up to the failure point. As important test variables, the anchorage type (new/conventional) and the prestress levels in the steel rebar (0, 50, and 100 kN) were selected. To investigate the strengthening effects based on these test variables, the deflection, strain, and failure mode were recorded, and then the load, ductility index, and energy ratio were analyzed. Test results showed that the newly proposed end anchorage had better strengthening effects and a greater inelastic energy than the conventional end anchorages.
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  • Experimental Study on the Flexural Behavior of Steel-Textile-Reinforced Concrete:Various Textile Reinforcement Details

    You, Jungbhin   Park, Jongho   Park, Sun-Kyu   Hong, Sungnam  

    In this study, one reinforced concrete specimen and six textile reinforced concrete (TRC) specimens were produced to analyze the flexural behavior of steel-textile-reinforced concrete. The TRC specimen was manufactured using a total of four variables: textile reinforcement amount, textile reinforcement hook, textile mesh type, textile lay out form. Flexural performance increases with textile reinforcement amount, textile reinforcement hook type and textile reinforcement mesh type. The flexural performance was improved when physical hooks were used. Furthermore, textile reinforcement was verified as being effective at controlling the deflection.
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  • BST106 Protects against Cartilage Damage by Inhibition of Apoptosis and Enhancement of Autophagy in Osteoarthritic Rats.

    Hong, Jeong-Min   Shin, Jun-Kyu   Kim, Jeom-Yong   Jang, Min-Jung   Park, Sun-Kyu   Lee, Jong-Hoon   Choi, Jung-Hyo   Lee, Sun-Mee  

    Chrysanthemum zawadskii var. latilobum (CZ) has been used as a traditional medicine in Asian countries for the treatment of inflammatory diseases. Recently, CZ extract was shown to inhibit differentiation of osteoclasts and provide protection against rheumatoid arthritis. The aim of this study was to investigate the molecular mechanisms of BST106, the ethanol extract of CZ, for cartilage protection in monosodium iodoacetate (MIA)-induced osteoarthritis (OA), particularly focusing on apoptosis and autophagy. BST106 (50, 100, and 200mg/kg) was orally administered once daily to MIA-induced OA rats. Swelling, limping, roentgenography, and histomorphological changes were assessed 28d after MIA injection. Biochemical parameters for matrix metalloproteinase (MMP), apoptosis, and autophagy were also assessed. BST106 ameliorated the severity of swelling and limping after MIA injection. Roentgenographic and histomorphological examinations revealed that BST106 reduced MIA-induced cartilage damage. BST106 decreased MIA-induced increases in MMP-2 and MMP-13 mRNA levels. Increased levels of serum cartilage oligomeric matrix protein and glycosaminoglycan release were attenuated by BST106. Furthermore, BST106 suppressed the protein expression of proapoptotic molecules and increased the protein expression of autophagosome- and autolysosome-related molecules. These findings indicate that BST106 protects against OA-induced cartilage damage by inhibition of the apoptotic pathway and restoration of impaired autophagic flux.=20
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  • Experimental Study of Flexural Behavior of Reinforced Concrete Beam Strengthened with Prestressed Textile-Reinforced Mortar

    Park, Jongho   Park, Sun-Kyu   Hong, Sungnam  

    In this study, nine specimens were experimentally tested to analyze the strengthening efficiency of textile-reinforced mortar (TRM) and the difference in flexural behavior between prestressed and non-prestressed TRM-strengthened reinforced concrete beam. The test results show that TRM strengthening improves the flexural strength of TRM-strengthened reinforced concrete beams with alkali-resistant-(AR-) glass textile as well as that with carbon textile. However, in the case of textile prestressing, the strengthening efficiency for flexural strength of the AR-glass textile was higher than that of the carbon textile. The flexural stiffness of AR-glass textiles increased when prestressing was introduced and the use of carbon textiles can be advantageous to reduce the decreasing ratio of flexural stiffness as the load increased. In the failure mode, textile prestressing prevents the damage of textiles effectively owing to the crack and induces the debonding of the TRM.
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  • The dorsal striatum expressing adenylyl cyclase-5 controls behavioral sensitivity of the righting reflex to high-dose ethanol

    Kim, Kyoung-Shim   Kim, Hannah   Park, Sun-Kyu   Han, Pyung-Lim  

    High-dose ethanol inflicts sedation and loss of righting reflex (LORA). Recently, it was reported that AC5 knockout (AC5(-/-)) mice consumed more ethanol and showed reduced sensitivity to high-dose ethanol compared to wild-type mice. As an extension of the previous study, in the present study we examined the signaling mechanism regulating altered behavioral sensitivity of LORR in AC5(-/-) mice. AC5(-/-) mice had enhanced phosphorylation of the NR2B subunit of NMDA receptors in the dorsal striatum and a partial reduction of MK801 (NMDA receptor antagonist)/ethanol-induced LORR. AC5(-/-) mice showed increased levels of phospho-CaMKII alpha, phospho-CREB, and BDNF in the dorsal striatum. CaMKII alpha(+/-) or BDNF+/- mice displayed enhanced LORR, a behavioral phenotype opposite to that displayed by AC5-/- mice. Consistently with these results, stereotaxic infusion of KN62 (CaMKII inhibitor), siRNA-CaMKII alpha, or siRNA-BDNF, within the dorsal striatum was sufficient to prolong LORR. These results suggest that neural mechanism is important for regulating behavioral sensitivity of LORR and that the signaling pathway(s) interplayed by AC5, CaMKII alpha and BDNF within the dorsal striatum is important for regulating the duration of ethanol-induced LORR. (c) 2012 Elsevier B.V. All rights reserved.
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    Provided are a connection apparatus and a connection method capable of rapidly and fixing a pre-cast deck slab with a beam. The connection apparatus includes a main body buried in the pre-cast deck slab and having a hollow part formed in an axial direction thereof! a plurality of support portions integrally formed with an outer surface of the main body, each of which has a body having a certain length and a hook integrally formed with an end of the body; a bolt having a bolt body inserted into the hollow part of the main body and a fixing hole of the beam, and a head integrally formed with an upper end of the bolt body! and a nut threadedly engaged with the bolt body of the bolt.
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  • Experimental Study on Flexural Behavior of TRM-Strengthened RC Beam:Various Types of Textile-Reinforced Mortar with Non-Impregnated Textile

    Park, Jongho   Hong, Sungnam   Park, Sun-Kyu  

    In this study, to compare strengthening efficiency and flexural behaviors of textile- reinforced mortar (TRM) according to various types of strengthening methods without the textile being impregnated, ten specimens were tested. The results showed that TRM was beneficial for uniform distribution of cracks and increased the strengthening efficiency and load-bearing capacity, as textile reinforcement ratio and textile lamination increased and the mesh size of the textile decreased and mechanical end anchorage applied. However, the strengthening effect was shown obviously until the yield load considering structural safety and serviceability.
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  • A novel indirect tensile test method to measure the biaxial tensile strength of concretes and other quasibrittle materials RID A-6157-2012

    Zi, Goangseup   Oh, Hongseob   Park, Sun-Kyu  

    A novel indirect tensile test method, the biaxial flexure test (BFT) method, has been developed to measure the biaxial tensile strength of concretes. The classical modulus of rupture (MOR) test has been generalized to three dimensions. In this method, we use a circular plate as the new test specimen. This plate is supported by an annular ring. We apply an external load to this specimen through a circular edge. The centers of the specimen, the loading device and the support are identical. The biaxial tensile strength measured by this new method is about 19% greater than the uniaxial tensile strength obtained from the classical modulus of rupture test as reported by other researchers. However, at the same time, we also found that the stochastic deviation of the biaxial tensile strength is about 63% greater than the uniaxial strength. (C) 2008 Elsevier Ltd. All rights reserved.
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  • Effect of prestress and transverse grooves on reinforced concrete beams prestressed with near-surface-mounted carbon fiber-reinforced polymer plates

    Hong, Sungnam   Park, Sun-Kyu  

    The effects of prestress levels on the flexural behavior of concrete beams strengthened with near surface-mounted (NSM) fiber-reinforced polymers (FRPs) were experimentally evaluated. Eight beams were tested. Failure of the prestressed strengthened beams occurred because of concrete cover separations at one end of the carbon FRP (CFRP) plates. With increasing prestress levels, the cracking, yield, and ultimate loads of the beams increased. The effect on the deflection corresponding to the cracking and yield loads was not significant; however, the ultimate deflections were affected by prestressing. The recommended prestress level for the concrete beams was <=3D 50% of the CFRP rupture strength. (C) 2016 Elsevier Ltd. All rights reserved.
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  • Evaluation of Long-Term Performance for Bonded Natural Stone Pavement Using Accelerated Pavement Test [Part II:Skid Resistance,Response of Deflection and FEM Analysis]

    Gong, Junho   Han, Eui-Seok   Park, Sun-Kyu   Cho, Dooyong  

    Natural stone-paved roads have been generally used to preserve historical regions due to its architectural aesthetic aspect and environmental impact. However, there are limitations of travelling speed and traffic volume owing to the defects caused by the increased traffic loading and volume. To deal with these hindrances, ultra-rapid-hardening cement for both jointing and laying course materials in rigid small element pavement was considered. The objective of the present study was to continuously evaluate and compare the long-term performance of the suggested bound stone pavement throughout the various test criteria such as skid resistance and FallingWeight Deflectometer tests. The skid resistance outcome was met to the requirement and the response of deflection was measured following by related test method. To compare rut depth, the Finite Element Method (FEM) analysis was performed by modelling with material properties and by creating the loading cycle for imitating the Accelerated Pavement Testing (APT). The maximum deflections of asphalt, concrete block, stone A and stone B were calculated to 17.7, 6.1, 6.3, and 3.6 mm, respectively. Compared to the final outcomes of APT and FEM analysis, there was a difference ranging from 2.1 to 2.3 mm in bound stone pavement B and A, respectively.
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  • Mechanical Property Evaluation of Sn-3.0A-0.5Cu BGA Solder Joints Using High-Speed Ball Shear Test

    Ha, Sang-Su   Jang, Jin-Kyu   Ha, Sang-Ok   Kim, Jong-Woong   Yoon, Jeong-Won   Kim, Byung-Woo   Park, Sun-Kyu   Jung, Seung-Boo  

    The traditional ball shear test is not suitable for evaluating joint reliability under drop loading, since the applied test speeds, usually lower than 5 mm/s, are well below the impact velocity applied to the solder joint in a drop test. The present study expands recently reported research by investigating the effect of thermal aging on the joint strength and fracture mode of Sn-3.0Ag-0.5Cu ball grid arrays during high-speed shear testing, with a shear height of 50 mu m and a shear speed ranging from 0.01 m/s to 3 m/s. The test specimens were aged at 393 K for 1000 h. After reflow, a (Ni,Cu)(3)Sn(4) intermetallic compound (IMC) layer was observed at the solder/Ni-P interface and the thickness of the IMC layer was increased through the aging process. The shear strength increased with increasing shear speed. The fracture surface of the solder joints showed three different fracture modes according to the shear speed and aging time. The fracture mode changed from ductile fracture to brittle fracture with increasing shear speed.
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