• Journal of Korean Association for Spatial Structures
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• v.10 no.2
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• pp.105-115
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• 2010

Recently, High-rise building are irregular-shaped to be city landmarks and function as vertical cities to enable the efficient use of land. 3T (Twisted, Tilted & Tapered) designs are being suggested for irregular buildings and studies to develop new structural system have been actively made to satisfy slender shape ratio. In diagrid system, not only gravity load but also lateral load is delivered based on the triangular shape of diagrid, so most of columns are eliminated. Because shearing force is delivered by the axial behavior (tensile/compressive) of diagrid to minimize shearing deformation, the system is more applicable to irregular buildings than existing system where shearing force is delivered by the columns. In this study, the process of selecting connection details and the structural safety of the selected details are verified using the finite element analysis with focus given to the construction overview of the Cyclone Tower. However, the relersed methods of stress concentration are suggested and the performance of stress concentration relieves that it's suggested for the appropriate cap plate thickness and extended length.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.6
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• pp.999-1010
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• 2016

High-strength strands have been increasingly applied to recent actual structures in Korea. Structural effect of the increased spacing of sheaths was investigated in this study when the usual 1,860 MPa strands of an LNG storage tank are replaced with 2,400 MPa high-strength strands. First, finite element models of a cylindrical wall of an LNG tank were established and prestressing effect of the circumferential and vertical tendons was considered as equivalent loads. As a result of varying the tendon spacing and prestressing force with the total prestressing effect kept the same, the stress distribution required in design was obtained with the high-strength strands. Also, a full-scale specimen that corresponds to a part of an LNG tank wall was fabricated with 31 high-strength strands with 15.2 mm diameter inserted in each of two sheaths. It was observed that such a high level of prestressing force can be properly transferred to concrete. Moreover, an LNG tank with the world's largest 270,000 kl capacity was modeled and the prestressing effect of high-strength strands was compared with that of normal strands. The watertightness specifications such as residual compressive stress and residual compression zone were also ensured in case of leakage accident. The results of this study can be effectively used when the 2,400 MPa high-strength strands are applied to actual LNG tanks.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.59-59
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• 2010

Graphene is a 2-D sheet of $sp^2$-bonded carbon arranged in a honeycomb lattice. This material has attracted major interest, and there are many ongoing efforts in developing graphene devices because of its high charge mobility and crystal quality. Therefore clear understanding of the substrate effect and mechanism of synthesis of graphene is important for potential applications and device fabrication of graphene. In a published paper in J. Phys. Chem. C (2008), the effect of substrate on the atomic/electronic structures of graphene is negligible for graphene made by mechanical cleavage. However, nobody shows the interaction between Ni substrate and graphene. Therefore, we have studied this interaction. In order to studying these effect between graphene and Ni substrate, We have observed graphene synthesized on Ni substrate and graphene transferred on $SiO_2$/Si substrate through Raman spectroscopy. Because Raman spectroscopy has historically been used to probe structural and electronic characteristics of graphite materials, providing useful information on the defects (D-band), in-plane vibration of sp2 carbon atoms (G-band), as well as the stacking orders (2D-band), we selected this as analysis tool. In our study, we could not observe the doping effect between graphene and Ni substrate or between graphene and $SiO_2$/Si substrate because the shift of G band in Raman spectrum was not occurred by charge transfer. We could noticed that the bonding force between graphene and Ni substrate is more strong than Van de Waals force which is the interaction between graphene and $SiO_2$/Si. Furthermore, the synthesized graphene on Ni substrate was in compressive strain. This phenomenon was observed by 2D band blue-shift in Raman spectrum. And, we consider that the graphene is incommensurate growth with Ni polycrystalline substrate.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.75-82
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• 2021

The objective of this study is to examine the loss of prestressing stress in the developed prestressing reinforcing units using steel bar and pipe (SP). The main parameters were the reinforcing bar type, the magnitude of prestressed force, and prestressing method. The test results showed that the loss of prestressing stress for SP was highest in the initial prestressing step, which was higher for the compression introduction typed specimens than tension introduction typed specimens. The loss of prestressing stress of SP made with P800 was 1.6% for the compression introduction typed specimen with 0.8f_y, which was lowest than the other specimens. Meanwhile, the relaxation of SP with the respect to the time ranged between 0.4 and 1.9%, irrespective of SP material type, the magnitude of prestressed force, and prestressing method. These values were less than 2.5%, which is the maximum value for the relaxation of prestressed reinforcing steel bars in design codes. Consequently, considering the loss of stress developed in the initial prestressing step, the developed SP material type, prestressing introduction method, and magnitude are recommended to be P800, compression introduction type, and 0.8f_y.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.269-275
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• 2019

As the national industry is developing gradually due to the expansion of the economic scale, the construction of large and super high-rise structures for building social infrastructure has been increasing, and studies have been conducted actively to transmit the large loads at the upper portion to the lower bedrock. In this study, the PHC was extended to an ultra-high strength PHC, which increased the concrete compressive strength of the PHC from the conventional 80 MPa to 110 MPa, and the PHC, which extended the tip of the pile. After construction with the driving method and injected pile method, the tendency of the bearing capacity was tested through a load test. Measurements of the bearing capacity of the extended PHC using the pile driving method revealed the main surface friction force to be smaller than that of the general PHC, and the stet-up effect was also insignificant. On the other hand, the effect of the friction force on the ground surface when the injected pile method was applied is expected to increase the bearing capacity when the gap between the main surface and the ground is wide and the cement paste is filled tightly. In addition, the ultrahigh strength PHC showed higher bearing capacity than the conventional PHC, and the permissible pile stress was less than 60%. Therefore, it is possible to reduce the number of piles and reduce the construction cost and effect of shortening the length of the pile by designing the tip of the pile on the ground with the intensity of soft rock as a method for utilizing the increased strength of the ultra-high strength PHC.

• Journal of Korean Society of Steel Construction
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• v.16 no.2 s.69
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• pp.215-224
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• 2004

The inelastic lateral-torsional buckling behavior of the beam-columns and the columns was investigated in this paper. The energy method was deployed to study the inelastic buckling behavior of the beam-columns and columns. which requires the iterative solution of a fourth-order eigenproblem. Hitherto, the patterns of residual stress that satisfies the I-section manufacturing in Korea is not available, therefore the pattern of residual stress used in this study is a 'well-known' simplified pattern. The simplified pattern of the residual stresses is incorporated with the flow theory of plasticity to model the inelastic response. Firstly, this study investigates the inelastic lateral-torsional buckling behavior of the I-section beam-columns under a concentric axial compressive force and uniform bending, and the effect of residual stress on the inelastic buckling behavior of beam-columns is studied. The study is then extended to the inelastic buckling of the columns by eliminating a bending moment. These results are compared it with the design method in the Korean Steel Designers Manual (KSDM 1995). This study has found that design method in KSDM (1995) is excessively conservative.

• Journal of Korean Society of Steel Construction
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• v.17 no.3 s.76
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• pp.357-363
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• 2005

There is a great need for high-strength steel especially for the high-rise steel building structure. High-strength steels, however, may have mechanical properties that are significantly different from those of the conventional steels. The application of high-strength steels to building structures should be reviewed as to whether the inelastic behavior equivalent to that of conventional steels can be attained or not. In this study, SM570TMC steel was tested to evaluate buckling strength under axial compressive force. The comparison tests for local buckling strength evaluation of box-type and H-shaped welded columns were performed with variable width-thickness ratios. As for the experimental check, the maximum strength of stub column was determined by local buckling as far as the limit of width-to-thickness ratio was satisfied with current design codes. Also, the strength of the stub column did not decrease suddenly by local buckling before maximum strength even when the ratio is not satisfied. The buckling strength of SM570TMC steel was higher than both ASD (Allowable Stress Design) and LRFD (Load and Resistance Factor Design) specifications.

• Korean Journal of Poultry Science
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• v.29 no.1
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• pp.45-52
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• 2002

Cryoprotective effects on chicken surimi during storage were investigated. Chicken surimi from mechanically deboned spent layer meat was prepared with 4 volumes of 0.5% NaCl washing, and then blended with or without cryoprotectants (8% trehalose, 8% oligosaccharide) prior to frozen storage at $-18^{\circ}C$ to 10 weeks Redness (a) of all surimi decreased during storage. Color stability increased during storage when lightness increased but redness decreased. At this Point, surimi maintained a better color quality as followed order; trehalose > oligosaccharide ) non-additive. Gel strength such as compressive force, hardness, adhesiveness and gumminess tended to decrease during frozen storage. Cryoprotectants provided significantly better textural properties than non-auditive. Surimi with trehalose showed the highest adhesiveness. In conclusion, trehalose and oligosaccharide seemed to be good cryoprotectants of chicken surimi. Especially, trehalose resulted in better cryoprotectant than oligosaccharide because of better color stability, better textural properties, and lower sweet characteristics.

• The korean journal of orthodontics
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• v.43 no.6
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• pp.294-301
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• 2013

Objective: To determine the interleukin (IL)-6 levels in gingival crevicular fluid (GCF) of patients with severe root resorption after orthodontic treatment and investigate the effects of different static compressive forces (CFs) on IL-6 production by human periodontal ligament (hPDL) cells and the influence of IL-6 on osteoclastic activation from human osteoclastic precursor (hOCP) cells in vitro. Methods: IL-6 levels in GCF samples collected from 20 patients (15 and 5 subjects without and with radiographic evidence of severe root resorption, respectively) who had undergone orthodontic treatment were measured by ELISA. The levels of IL-6 mRNA in hPDL cells and IL-6 protein in conditioned medium after the application of different uniform CFs (0, 1.0, 2.0, or 4.0 $g/cm^2$ for up to 72 h) were measured by real-time PCR and ELISA, respectively. Finally, the influence of IL-6 on mature osteoclasts was investigated by using hOCP cells on dentin slices in a pit-formation assay. Results: Clinically, the IL-6 levels were significantly higher in the resorption group than in the control group. In vitro, IL-6 mRNA expression significantly increased with increasing CF. IL-6 protein secretion also increased in a time- and magnitude-dependent manner. Resorbed areas on dentin slices were significantly greater in the recombinant human IL-6-treated group and group cultured in hPDL cell-conditioned medium with CF application (4.0 $g/cm^2$) than in the group cultured in hPDL cell-conditioned medium without CF application. Conclusions: IL-6 may play an important role in inducing or facilitating orthodontically induced inflammatory root resorption.

• Geomechanics and Engineering
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• v.16 no.4
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• pp.385-397
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• 2018

This study evaluates the interfacial properties of composite specimens consisting of shotcrete and sprayed waterproofing membrane. Two different membrane prototypes were first produced and tested for their waterproofing ability. Then composite specimens were prepared and their interfacial properties assessed in direct shear and uniaxial compression tests. The direct shear test showed the peak shear strength and shear stiffness of the composites' interface decreased as the membrane layer became thicker. The shear stiffness, a key input parameter for numerical analysis, was estimated to be 0.32-1.74 GPa/m. Shear stress transfer at the interface between the shotcrete and membrane clearly emerged when measuring peak shear strengths (1-3 MPa) under given normal stress conditions of 0.3-1.5 MPa. The failure mechanism was predominantly shear failure at the interface in most composite specimens, and shear failure in the membranes. The uniaxial compression test yielded normal stiffness values for the composite specimens of 5-24 GPa/m. The composite specimens appeared to fail by the compressive force forming transverse tension cracks, mainly around the shotcrete surface perpendicular to the membrane layer. Even though the composite specimens had strength and stiffness values sufficient for shear stress transfer at the interfaces of the two shotcrete layers and the membrane, the sprayed waterproofing membrane should be as thin as possible whilst ensuring waterproofing so as to obtain higher strength and stiffness at the interface.