• Steel and Composite Structures
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• v.38 no.6
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• pp.739-749
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• 2021

This paper introduces an improved design equation to evaluate the resisting capacity of circular reinforced concrete (RC) columns partially strengthened with outer steel tube. When RC column members are required to be strengthened according to the change in the loadings considered and/or the deterioration progress in columns, wrapping up RC column with steel circular tube, which takes the form of concrete filled steel tube (CFST), has been popularly considered because of its structural advantage induced from the confinement effect. However, the relatively high construction cost of steel tube is restricting its use to the required region, while deriving the shape of a partial CFST column. To evaluate the resisting capacity of a partial CFST column, numerical analyses need to be performed, and a numerical model proposed in the previous study for the numerical analysis of full CFST columns is used to conduct parametric studies for the introduction of a design equation. The bond-slip effect developed along the interface between the in-filled concrete and the exterior steel tube is taken into consideration and the validity of the numerical model has been established through correlation studies between experimental data and numerical results for partial CFST circular columns. Moreover, parametric studies make it possible to introduce a design equation for determining the optimum length of outer steel tube which produces partial CFST circular columns.

• Applied Chemistry for Engineering
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• v.20 no.3
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• pp.317-321
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• 2009

In order to analyze the high temperature phase formation and the sinterability of super ionic conductor $K^+-{\beta}/{\beta}"-Al_2O_3$ which is commonly used as a solid oxide electrolyte, the pure $K^+-{\beta}/{\beta}"-Al_2O_3$ powder in the ternary system $K_2O-LiO_2-Al_2O_3$ was synthesized by solid state reaction and formed to tube and disk using slip casting method and cold isostatic pressing (CIP), respectively. The slip casting was conducted in an alumina mold with the slurry containing 40 wt% of solid contents and the CIP was carried out under 20 MPa. The samples were sintered at $1600^{\circ}C$, $1700^{\circ}C$ and $1750^{\circ}C$, respectively, and their phase formation and the sintering density were investigated according to the forming method. The samples produced by CIP showed far higher ${\beta}"-Al_2O_3$ fraction as compared with those by slip casting. On the other hand, the samples by slip casting showed slightly higher sintering density. The relative density reached to about 83% at $1750^{\circ}C$ and for 1 h, independent of the forming method. In the case of 90 min socking time, the density was decreased owing to the exaggerated grain growth and the pores by $K_2O$ evaporation.

• Tribology and Lubricants
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• v.21 no.1
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• pp.33-38
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• 2005

Fretting is the oscillatory motion with very small amplitudes, which usually occurs between two solid surfaces in contact. Fretting wear is the removal of material from contacting surfaces through fretting action. Fretting wear of steam generator tubes in nuclear power plant becomes a serious problem in recent years. The materials for the tubes usually are Inconel 690 (I-690) and Inconel 600 (I-600). In this paper, fretting wear tests for I-690 and I-600 were performed under various applied loads in water at room temperature. Results showed that the fretting wear loss of I-690 and I-600 tubes was largely influenced by stick-slip. The fretting wear mechanisms were the abrasive wear in slip regime and the delamination wear in stick regime. Also, I-690 had somewhat better wear resistance than I-600.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.3
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• pp.37-46
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• 2013

Recent years have witnessed the use of micro shock tube in various engineering applications like micro combustion, micro propulsion, particle delivery systems etc. The flow characteristics occurring in the micro shock tube shows a considerable deviation from that of well established conventional macro shock tube due to very low Reynolds number and high Knudsen number effects. Also the diaphragm rupture process, which is considered to be instantaneous process in many of the conventional shock tubes, will be crucial for micro shock tubes in determining the near diaphragm flow field and shock formation. In the present study, an axi-symmetric CFD method has been applied to simulate the micro shock tube, with Maxwell's slip velocity and temperature jump boundary conditions. The effects of finite diaphragm rupture process on the flow field and the shock formation was investigated, in detail. The results show that the shock strength attenuates rapidly as it propagates through micro shock tubes.

• Nuclear Engineering and Technology
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• v.17 no.4
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• pp.279-289
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• 1985

The purpose of this paper is to investigate the density-wave oscillation type instability in the recirculating loop of U-tube steam generator (UTSG). The perturbed and nodalized conservations equations based on the drift-flux model have been derived to obtain the single-and two-phase pressure drop perturbations, by taking into account the slip between phases, nonuniform heat flux and heated wall dynamics. To assess the stability, the frequency domain technique with the Nyquist criterion has been used under the constant pressure drop boundary condition through the loop. The computer implementation of this model, SASG, was used for the parametric study of the steam generator in Kori-Unit 1. The results of the parametric study revealed important factors influencing UTSG stability margin.

• The KSFM Journal of Fluid Machinery
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• v.10 no.1 s.40
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• pp.56-63
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• 2007

Because the mixing efficiency is influenced remarkably by varying the geometrical configurations, the study of flow characteristics inside the mechanical agitator is very important to improve the performances. The draught tube in the agitator makes intermixing between the screw and tube by interrupting radial flow, and it makes circulation region in a mixing chamber. In general, the helical screw agitator with a draught tube (HSA) is proved more efficient to mix than the others. Consequently, such as the shapes of helical screw, number of pitches and the variation of angular velocity are the main parameters for improving the capacity of HSA. And also the suspension of the solid particles in the agitator can be determined these parameters. The rate of solids suspension in the mixing chamber was quantified with a statistical average value, of. Numerical analyses were carried out, using a commercial CFD code, Fluent, to obtain the velocity, pressure and particle distributions under steady, laminar flow and no-slip conditions. Results are graphically depicted with various parameters.

• Journal of the Korea Concrete Institute
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• v.16 no.1 s.79
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• pp.61-69
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• 2004

The bridge piers under service suffered a brittle failure due to the deterioration of lap-spliced longitudinal reinforcement without developing its flexural capacity or ductility. The earthquake induced lateral force results in tension which causes bond-slip failure at the lap-spliced region in circular bridge piers. In this case, such a brittle failure can be controlled by the seismic retrofit using FRP laminated circular tube. The retrofitted piers using FRP laminated circular tube showed significant improvement in seismic performance due to FRP's confinement effect. This paper presents the analytical results on the seismic strengthening effect of circular bridge piers with poor lap-splice details and strengthened with FRP laminated circular tube. FRP's confinement effect is predicted by the classical elasticity solution for the laminated circular tube manufactured with several layers. The FRP laminated circular tube induces the flexural failure instead of a bond-slip failure of the circular reinforced concrete piers under seismic induced lateral forces. To investigate the correctness and effectiveness of analytical solution derived in this study, the analytical results were compared with the experimental data and it was confirmed that the results were correlated well each other, The effects on the confinement of FRP laminated circular tube, such as the number of layers, the fiber orientations, and the mechanical properties, were investigated. From the parametric study, it was found that the number of layers, the fiber orientations, and the major Young's modulus (E11) of the FRP laminated circular tube were the dominant parameters affecting the confinement of reinforced concrete circular bridge piers.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.05a
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• pp.63-70
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• 2002

Wear on the tube-to-spring contact is investigated experimentally. The wear is caused by the vibration of the tube while the springs support it. As for the supporting conditions, applied are the contacting normal force (P) of 5 N, just-contact (P = 0 N) and the gap of 0.1 mm. The gap condition is tried far considering the influence of simultaneous impacting and sliding on wear. Results show that the wear volume increases in the order of the gap, the just-contact and the 5 N conditions. This is explained from the contact geometry of the spring, which is convex of smooth contour. The contact shear force is regarded smaller in the case of the gap existence compared with the other conditions. Wear mechanism is considered from SEM observation of the worn surface. The variation of the normal contact traction is analysed using the finite element analysis to estimate the slip displacement range on the contact with consulting the fretting map previously obtained.

• Structural Engineering and Mechanics
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• v.75 no.6
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• pp.643-657
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• 2020

This study presents experimental and numerical investigations on circular steel tube confined ultra high performance concrete (UHPC) columns under axial compression. The plain UHPC without fibers was designed to achieve a compressive strength ranged between 150 MPa and 200 MPa. Test results revealed that loading on only the UHPC core can generate a significant confinement effect for the UHPC core, thus leading to an increase in both strength and ductility of columns, and restricting the inherent brittleness of unconfined UHPC. All tested columns failed by shear plane failure of the UHPC core, this causes a softening stage in the axial load versus axial strain curves. In addition, an increase in the steel tube thickness or the confinement index was found to increase the strength and ductility enhancement and to reduce the magnitude of the loss of load capacity. Besides, steel tube with higher yield strength can improve the post-peak behavior. Based on the test results, the load contribution of the steel tube and the concrete core to the total load was examined. It was found that no significant confinement effect can be developed before the peak load, while the ductility of post-peak stage is mainly affected by the degree of the confinement effect. A finite element model (FEM) was also constructed in ABAQUS software to validate the test results. The effect of bond strength between the steel tube and the UHPC core was also investigated through the change of friction coefficient in FEM. Furthermore, the mechanism of circular steel tube confined UHPC columns was examined using the established FEM. Based on the results of FEM, the confining pressures along the height of each modeled column were shown. Furthermore, the interaction between the steel tube and the UHPC core was displayed through the slip length and shear stresses between two surfaces of two materials.

• KSTLE International Journal
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• v.3 no.1
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• pp.49-53
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• 2002

Inconel 690 for nuclear steam generator tube has more chromium than the conventionally used Inconel 600 in order to increase the corrosion resistance. TD evaluate the tribological characteristics under fretting condition the fretting tests as well as sliding tests were carried out in elevated temperature water environment. Fretting tests of the cross-cylinder type were done under various vibrating amplitudes and applied normal loads in order to measure the friction forces and wear volumes. Also, the conventional sliding tests of pin-en-disk type were carried out to compare the test results. In fretting, the friction was very sensitive to the load and the amplitude. The friction coefficient decreased with increasing load and decreasing amplitude. Also, the wear of Inconel 690 can be predictable using the work rate model. Depending on normal loads and vibrating amplitudes, distinctively different wear mechanisms and of ten drastically different wear rates can occur. It was fecund that the fretting wear coefficients in water were increased as increasing the temperature of water.