• The Journal of Korean Academy of Prosthodontics
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• v.59 no.2
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• pp.153-163
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• 2021

Purpose: The aim of this study was to evaluate the effects of four surface treatment methods to improve zirconia roughness and three types of resin cement on the shear bond strength (SBS). Materials and methods: A total of 120 zirconia blocks were randomly divided into four surface treatments: non-treatment (Control), airborne-particle abrasion (APA) with 50 ㎛ Al2O3 (APA50), APA with 125 ㎛ Al2O3 (APA125), and ZrO2 slurry (ZA). Three resin cements (Panavia F 2.0, Superbond C&B, and Variolink N) were applied to the surface-treated zirconia specimens. All specimens were subjected to SBS testing using a universal testing machine. The surface of the representative specimens of each group was observed by scanning electron microscope (SEM). SBS data were analyzed with oneway ANOVA, two-way ANOVA test and post-hoc Tukey HSD Test (α=.05). Results: In the surface treatment method, APA125, APA50, ZA, and Control showed high shear bond strength in order, but there was no significant difference between APA125 and APA50 (P>.05). Also, ZA showed significantly higher shear bond strength than Control (P<.05). In the resin cement type, Panavia F 2.0, Superbond C&B, and Variolink N showed significantly higher shear bond strength in order (P<.05). In SEM images, the zirconia surfaces of the APA50 and APA125 showed quite rough and irregular shapes, and the zirconia surface of the ZA was observed small irregular porosity and rough surfaces. Conclusion: APA and ZrO2 slurry were enhanced the surface roughness of zirconia, and Panavia F 2.0 containing MDP showed the highest shear bond strength with zirconia.

• Journal of Korean Society of Steel Construction
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• v.14 no.1
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• pp.87-94
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• 2002

In the preceding study, a series of results was presented according to factors like as attaching method of main bar, shear span to depth ratio, reinforcing method for different types of region among various factors, which could determine the properties of composite beams. Based on these results, this study was planned to investigate the structural behaviors of according to attaching method of main bar for composite beams(end-reinforced concrete(RC), center-steel concrete (SC)) varying ratio of tensile bar to steel mainly. Consequently, there were little difference according to attaching method of main bar. And as the ratio of tensile bar to steel increase, the efficiency of strength was high, but ductile capacity of beams could deteriorate. Therefore, to maximize the structural properties of composite beams, it was considered that the ratio of tensile bar to steel should be limited.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.771-776
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• 2020

In this study, the flexural/shear behavior characteristics of perfobond FRP-concrete composite beams using an FRP plate with perforated webs as formwork and reinforcement are analyzed through an analytical method. Compared with the existing experimental results, we have proved its usefulness and use it in future practice. When the nonlinearity is very large in this case, the nonlinear finite element analysis by an explicit method will be effective. The concrete damage plasticity (CDP) model adopted in this study is considered to be able to adequately simulate the nonlinear behavior of concrete, and the determination of several variable factors required in the model is compared with the experimental results and values used in the study. This recommendation will require review and adjustment for more diverse cases. The effect of the perfobond of the composite beam with perforated web is considered to be somewhat effective in terms of securing the initial stiffness, but in the case of the apex, it is considered that the cross-sectional loss and the effect of improving the bonding force should be properly arranged. The contact problem, such as slipping of the FRP plate and concrete, is considered to be one of the reasons that the initial stiffness is slightly larger than the test result, and the slightly difference from the experimental results is attributed to the separation problem between concrete and FRP after the peak.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.4
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• pp.19-33
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• 2008

Dynamic response measurements from natural excitation were carried out for 25- and 42-story buildings to evaluate their inherent properties, such as natural frequencies, mode shapes and damping ratios. Both are reinforced concrete buildings adopting a core wall, or with shear walls as the major lateral force resisting system, but frames are added in the plan or elevation. In particular, shear walls in a 25-story building are converted to frames from the 4th floor level downwards while maintaining a core wall throughout, resulting in a fairly complex structure. Due to this, along with similar stiffness characteristics in the principal directions, significantly coupled and closely spaced modes of motion are expected in this building, making identification rather difficult. By using various state-of-the-art system identification methods, the modal parameters are extracted, and the results are then compared. Three frequency-domain and four time-domain based operational modal identification methods are considered. Overall, all natural frequencies and damping ratios estimated from the different identification methods showed a greater consistency for both buildings, while mode shapes exhibited some degree of discrepancy, varying from method to method. On the other hand, in comparison with analysis results obtained using the initial finite element(FE) models, test results exhibited a significant difference of about doubled frequencies, at least for the three lower modes in both buildings. To improve the correlation between test and analysis, a few manual schemes of FE model updating based on plausible reasons have been applied, and acceptable results are obtained. The advantages and disadvantages of each identification method used are addressed, and some difficulties that might arise from the updating of FE models, including automatic procedures, for such large structures are carefully discussed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5A
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• pp.519-529
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• 2009

Fiber reinforced composite materials have various advantages in mechanical and chemical aspects. Not only high fatigue and chemical resistance, but also high specific strength and stiffness are attained, and therefore, damping characteristics are beneficial to marine piles. Since piles used for marine structures are subjected to compression and bending as well, detailed research is necessary. Current study examine the mechanical behavior under flexural and/or compressive loads using concrete filled fiber reinforced plastic composite piles, which include large size diameter. 25 pile specimens which have various size of diameters and lengths were fabricated using hand lay-up or filament winding method to see the effect of fabrication method. The inner diameters of test specimens ranged from 165 mm to 600 mm, and the lengths of test specimens ranged from 1,350 mm to 8,000 mm. The strengths of the fill-in concrete were 27 and 40 MPa. Fiber volumes used in circumferential and axial directions are varied in order to see the difference. For some tubes, spiral inner grooves were fabricated to reduce shear deformation between concrete and tube. It was observed that the piles made using filament winding method showed higher flexural stiffness than those made using hand lay-up. The flexural stiffness of piles decreases from the early loading stage, and this phenomenon does not disappear even when the inner spiral grooves were introduced. It means that the relative shear deformation between the concrete and tube wasn't able to be removed.

• Structural Engineering and Mechanics
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• v.45 no.3
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• pp.311-321
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• 2013

In this study, to have a better judgment on the structural performance, the effects of dynamic Soil-Structure Interaction (SSI) on seismic behaviour and lateral structural response of mid-rise moment resisting building frames are studied using Finite Difference Method. Three types of mid-rise structures, including 5, 10, and 15 storey buildings are selected in conjunction with three soil types with the shear wave velocities less than 600m/s, representing soil classes $C_e$, $D_e$ and $E_e$, according to Australian Standard AS 1170.4. The above mentioned frames have been analysed under two different boundary conditions: (i) fixed-base (no soil-structure interaction), and (ii) flexible-base (considering soil-structure interaction). The results of the analyses in terms of structural lateral displacements and drifts for the above mentioned boundary conditions have been compared and discussed. It is concluded that the dynamic soil-structure interaction plays a considerable role in seismic behaviour of mid-rise building frames including substantial increase in the lateral deflections and inter-storey drifts and changing the performance level of the structures from life safe to near collapse or total collapse. Thus, considering soil-structure interaction effects in the seismic design of mid-rise moment resisting building frames, particularly when resting on soft soil deposit, is essential.

• Korean Journal of Adult Nursing
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• v.15 no.2
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• pp.267-277
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• 2003

Purpose: The purpose of this study was to evaluate the applicability of braden scale to assess pressure ulcer risk patients and to identify additional risk factors of pressure sores in an neurologic intensive care unit. Method: The subjects of this study were 66 patients in neurologic intensive care units. Data was prospectively collected from Sep. to Dec., 2002. Data were analyzed by mean, percentage, t-test, chi-square, discriminant analysis using Spss pc+. Result: The results of this study were as follows: 1) There was a significant difference between scoring of braden scale and pressure ulcer development. The subscales that predicted pressure ulcer development using braden scale only were sensory perception, moisture, mobility, friction & shear. By using these subscales, sensitivity was 86.7%, and specificity was 61.1%, and total hit ratio was 72.7%. 2) Additional pressure ulcer risk factors which showed significance for discriminating two group were protein, albumin, gender, level of consciousness, pattern of bowel elimination. By using the combination of these additional risk factors in addition to the braden scale, total hit ratio increased to 84.8%. Conclusion: This data suggest that albumin, protein, gender, level of consciousness, pattern of bowel elimination in addition to the braden scale should be included in the pressure sore assessment tool.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.183-190
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• 2009

The objective of this study is to get simulation data about pulsatile flow around an interior solid body inside a bifurcated tube. All the processes were based on CFD method, with a commercial FVM code, SC/Tetra ver. 6.0 for solving, and with CATIA R16 for generating geometries. The bifurcated tube models were drawn with the bifurcated angle of 45 degrees, considering Murray's law about the diameter ratio. With various locations of the object, the effects of flow on the drag were considered. For the pulsating flow condition, the velocity wave profile was given as the inlet boundary condition. To validate all the result, the simulation was compared with the existing data of the other papers first. Overall flow field of both data were similar, but there was some difference at a zero velocity. Therefore the next simulation was continued with the sine wave profiles where there is no negative flow, and then the data was compared with one of the pulmonary artery velocity where there is negative flow. The final process was to calculate flow variables such as the wall shear stress (WSS) and to compute the drag of the solid object.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.40 no.1
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• pp.31-38
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• 2007

This study investigated the fluid force acting on an artificial reef and the scour pattern at the bottom of the artificial reef in a steady-flow field using the finite difference method (Flow-3D). The structure was tetragonal in shape, like similar objects found in nature. The numerical analysis showed that the hydrodynamic characteristics and incipient scouring pattern matched natural phenomena. The velocity distribution around the tetragon was symmetric and wake occurred inside the tetragon and behind the bottom of the tetragon. The length of the recirculation flow behind the tetragon for each velocity was about 4-5 cm and the magnitude of the recirculation flow inside the tetragon generally increased with the Reynolds' number, although it decreased slightly for Reynolds' numbers from 11,000 to 12,000. In addition, the total fluid force acting on the tetragon increased with the inflow velocity, although the increment was smaller when the velocity exceed 18 cm/sec. The incipient pattern for the scouring of sediment matched the natural phenomenon.

• Journal of the Korean Society of Marine Environment & Safety
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• v.17 no.1
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• pp.23-28
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• 2011

This paper outlines extraction potential of tidal stream resources from the simplified channel in which flow is driven by a head difference between inlet and outlet. Energy extraction alters the flow within a simple channel, and extraction of 10% energy flux in a natural channel would give rise to a flow speed reduction of about 5.7%. If 20% of the undisturbed energy flux is extracted, the flow speed is reduced by 11.3%. The simple channel also suggests that extractable energy might be higher if flow speed reductions are considered acceptable.