• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2017.10a
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• pp.241-242
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• 2017

Part of the channel in L-shaped tunnel field-effect transistor (LTFET) is very thin and suffers from quantum confinement effect. Role of quantum confinement effect on band-to-band-tunneling (BTBT) of LTFET was investigated using numerical simulation and band diagram analysis. It was found that quantum confinement effect significantly affects the BTBT mechanism of LTFET devices.

• Steel and Composite Structures
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• v.31 no.1
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• pp.13-25
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• 2019

Reactive powder concrete (RPC) is a type of ultra-high strength concrete that has a relatively high brittleness. However, its ductility can be improved by confinement, and the use of RPC in composite RPC filled steel tube columns has become an important subject of research in recent years. This paper aims to present an experimental study of axial capacity calculation of RPC filled circular steel tube columns. Twenty short columns under axial compression were tested and information on their failure patterns, deformation performance, confinement mechanism and load capacity were presented. The effects of load conditions, diameter-thickness ratio and compressive strength of RPC on the axial behavior were further discussed. The experimental results show that: (1) specimens display drum-shaped failure or shear failure respectively with different confinement coefficients, and the load capacity of most specimens increases after the peak load; (2) the steel tube only provides lateral confinement in the elastic-plastic stage for fully loaded specimens, while the confinement effect from steel tube initials at the set of loading for partially loaded specimens; (3) confinement increases the load capacity of specimens by 3% to 38%, and this increase is more pronounced as the confinement coefficient becomes larger; (4) the residual capacity-to-ultimate capacity ratio is larger than 0.75 for test specimens, thus identifying the composite columns have good ductility. The working mechanism and force model of the composite columns were analyzed, and based on the twin-shear unified strength theory, calculation methods of axial capacity for columns with two load conditions were established.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.03a
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• pp.349-361
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• 2003

For performance-base design using nonlinear static analysis, it is required to predict the inelastic behavior of structural members accurately. In the present study, nonlinear numerical analysis was performed to develop the method describing the moment-curvature relationship of structural wall with boundary confinement. Through the numerical analysis, variations of behavioral characteristics and failure mechanism with the arrangement of vertical reiforcement and the length of boundary confinement were studied. Based on the findings, moment-curvature curves and curvature capacity for walls with a variety of re-bar arrangement was developed. By equalizing curvature capacity to demand, a design method which can determine the length of boundary confinement, was developed and for the effectiveness of boundary confinement and constructability, boundary confinement detail was proposed.

• Journal of the Korean Society for Railway
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• v.5 no.4
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• pp.244-252
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• 2002

We must notice ground movement by excavation for reasonable tunnel designs. The convergence confinement method is an attempt to evaluate tunnel stability conditions by means of a mathematical model and a ground response curve. In this study, the convergence confinement method by numerical model was examined. This method don't need the basic assumptions for a mathematical model of circular tunnel shape, and hydrostatic in situ stress. Also modified ground response curve that is calculated after installing the support, is suggested, which informs us the ground movement mechanism. The ground response curve and the support reaction curve are mutually dependent. Especially the support reaction curve depends upon the ground response curve. The mechanism of tunnel must be analyzed by the interaction between support and ground. Consequently the stability of tunnel must be qualitatively investigated by a ground response curve and quantitatively adjudged by a numerical analysis for the reasonable design of tunnel.

• Structural Engineering and Mechanics
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• v.56 no.5
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• pp.727-743
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• 2015

According to former studies, the mechanical properties of reinforced concrete filled tubular steel (RCFT) columns differed greatly from that of concrete filled steel tubular (CFT) columns because of interaction of inserted reinforcement in RCFT. Employing an experiment-based verification policy, a general FE nonlinear analysis model was developed to analyze the mechanical behavior and failure mechanism of RCFT columns under uniaxial compression. The reasonable stress-strain relationships were suggested for confined concrete, reinforcements and steel tube in the model. The mechanism for shear failure of concrete core was found out in the numerical simulation, and a none-conventional method and equation for evaluating the confinement effect of RCFT were proposed.

• Steel and Composite Structures
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• v.51 no.6
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• pp.587-600
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• 2024

In order to investigate the seismic performance of regionally confined concrete circular column with trapezoid stirrups (TRCCC) under high axial compression ratio, the confinement mechanism of regionally confined concrete was analyzed. Three regionally confined concrete circular columns with trapezoid stirrups were designed, and low cyclic loading tests were conducted at three different axial compression ratios (0.9, 1.1, 1.25) to study the failure mode, hysteresis curve, skeleton curve, deformation capacity, stiffness degradation and energy dissipation capacity of the specimens. The results indicate that the form of regional confinement concrete provides more uniform confinement to the normal confinement, and the confinement efficiency at the edges is 1.4 times that of normal confined concrete. The ductility coefficients of the specimens were all greater than 3 under high axial compression ratios, and the stiffness and horizontal bearing capacity increased with the increase of axial compression ratio. Therefore, it is recommended that the code of design specifications can appropriately relax the axial compression ratio limit for TRCCC. Finally, the spacing between stirrups of TRCCC was analyzed using ABAQUS software. The results showed that as the spacing between the stirrups decreased, the cracking load and peak load of TRCCC increased continuously, but the rate of increase decreases.

• Journal of Korean Association for Spatial Structures
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• v.1 no.2 s.2
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• pp.67-74
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• 2001

This paper is to estimate the load carrying capacities of concrete-filled steel tubular columns and the important parameters are selected the size, length and concrete strength. he concrete-filled tube structures has many excellent structural properties, that is, high load capacity, good plastic deformation and high resistance local buckling. Under these background, this study Investigated to the structural compression behaviors, the maximum strength, the confinement effects, the fracture mechanism, local buckling failure and concrete strength effects.

• 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.

• Korean Chemical Engineering Research
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• v.59 no.4
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• pp.626-631
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• 2021

One of the nonlinear electrokinetic phenomena around ion exchange membrane is electroconvective instability which can be found in various electrokinetic applications such as electrodialysis, electrochemical battery, microfluidic analysis platform, etc. Such instability acts as a positive transport mechanism for the electrodialysis via amplifying mass transport rate. On the other hands, in the electrochemical battery and the microfluidic applications, the instability provokes unwanted mass transport. In this research, to control the electroconvective instability, the onset of the instability was analyzed as a function of confinement effect as well as applied voltage. As a result, we figured out that the dynamic behavior of electroconvective instability transited as a sequence of stable regime - static regime - chaotic regime depending on the applied voltage and confinement effect. Furthermore, stability curves about the dynamic transition were numerically determined as well. Conclusively, the confinement effect on electroconvective instability can be applied for effective means to control the electrokinetic chaos.

• Steel and Composite Structures
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• v.25 no.5
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• pp.545-556
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• 2017

The tubed steel reinforced concrete (SRC) column is a composite column in which the outer steel tube is mainly used to provide confinement on the core concrete. This paper presents experimental and analytical studies on the behavior of circular tubed SRC (TSRC) columns subjected to axial compression. Eight circular TSRC columns were tested to investigate the effects of length-to-diameter ratio (L/D) of the specimens, diameter-to-thickness ratio (D/t) of the steel tubes, and use of stud shear connectors on the steel sections. Elastic-plastic analysis on the steel tubes was used to investigate the mechanism of confinement on the core concrete. The test results indicated that the tube confinement increased the strength and deformation capacity for both short and slender columns, and the effects on strength were more pronounced for short columns. A nonlinear finite element (FE) model was developed using ABAQUS, in which the nonlinear material behavior and initial geometric imperfection were included. Good agreement was achieved between the predicted results using the FE model and the test results. The test and FE results were compared with the predicted strengths calculated by Eurocode 4 and the AISC Standard. Based on the analytical results, a new design method for this composite column was proposed.