• Journal of Korean Society of Steel Construction
• /
• v.27 no.3
• /
• pp.261-271
• /
• 2015

Steel concentrically braced frame is an efficient system that can acquire resistance against the lateral force of buildings with the least amount of quantity. In this study is intended to proceed on the research of schemes for reinforcement by supplementing previously installed H-formed brace with non-welded cold-formed plastic stiffening materials restricting the flexure and buckling and acquire a consistent strength on the tensile and compressive force. As for the measures of supplementing previously-installed inverted V-formed braced frame, stiffening materials in the previous studies were converted to weak-axial supplementing materials to suggest a specific scheme evaluating the structural function through an experiment of members, interpretation of members, and frame-focused experiment. Reinforced brace satisfied the requirement to be prevent AISC brace from being ruptured due to imbalanced strength in the beam.

• Proceedings of the Korean Vacuum Society Conference
• /
• 1999.07a
• /
• pp.216-216
• /
• 1999

The usage of a stationary plasma thruster (SPT) ion source, invented previously for space application in Russia, in experiments with surface modifications and film deposition systems is reported here. Plasma in the SPT is formed and accelerated in electric discharge taking place in the crossed axial electric and radial magnetic fields. Brief description of the construction of specific model of SPT used in the experiments is presented. With gas flow rate 39ml/min, ion current distributions at several distances from the source are obtained. These was equal to 1~3 mA/$\textrm{cm}^2$ within an ion beam ejection angle of $\pm$20$^{\circ}$with discharge voltage 160V for Ar as a working gas. Such an extremely high ion current density allows us to obtain the Ti metal films with deposition rate of $\AA$/sec by sputtering of Ti target. It is shown a possibility of using of reactive gases in SPT (O2 and N2) along with high purity inert gases used for cathode to prevent the latter contamination. It is shown the SPT can be operated at the discharge and accelerating boltages up to 600V. The results of presented experiments show high promises of the SPT in sputtering and surface modification systems for deposition of oxide thin films on Si or polymer substrates for semiconductor devices, optical coatings and metal corrosion barrier layers. Also, we have been tried to establish in application of the modeling expertise gained in electric and ionic propulsion to permit numerical simulation of additional processing systems. In this mechanism, it will be compared with conventional DC sputtering for film microstructure, chemical composition and crystallographic considerations.

• Steel and Composite Structures
• /
• v.22 no.4
• /
• pp.797-820
• /
• 2016

This paper simulates the hysteretic behavior of steel reinforced recycled concrete (SRRC) columns under cyclic loads using OpenSees software. The effective fiber model and displacement-based beam-column element in OpenSees is applied to each SRRC columns. The Concrete01 material model for recycled aggregate concrete (RAC) and Steel02 material model is proposed to perform the numerical simulation of columns. The constitutive models of RAC, profile steel and rebars in columns were assigned to each fiber element. Based on the modelling method, the analytical models of SRRC columns are established. It shows that the calculated hysteresis loops of most SRRC columns agree well with the test curves. In addition, the parameter studies (i.e., strength grade of RAC, stirrups strength, steel strength and steel ratio) on seismic performance of SRRC columns were also investigated in detail by OpenSees. The calculation results of parameter analysis show that SRRC columns suffered from flexural failure has good seismic performance through the reasonable design. The ductility and bearing capacity of columns increases as the increasing magnitude of steel strength, steel ratio and stirrups strength. Although the bearing capacity of columns increases as the strength grade of RAC increases, the ductility and energy dissipation capacity decreases gradually. Based on the test and numerical results, the flexural failure mechanism of SRRC columns were analysed in detail. The computing theories of the normal section of bearing capacity for the eccentrically loaded columns were adopted to calculate the nominal bending strength of SRRC columns subjected to vertical axial force under lateral cyclic loads. The calculation formulas of horizontal bearing capacity for SRRC columns were proposed based on their nominal bending strength.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.32 no.5C
• /
• pp.221-229
• /
• 2012

Steel ribs such as H-beam or lattice girder are often reinforced to secure the stability of NATM tunnel when the ground is in the bad condition. When designing, however, steel ribs are not often taken into consideration on the numerical analysis when they are regarded as temporary tunnel supports until shotcrete shows its best performance or if they are, there are various modeling methods. This study shows behavior and loading capacity of steel ribs and shotcrete through the strength test on the bending, pressure and full-scaled. Also, we conducted and analyzed the experiment of composite member consisting of shotcrete and steel ribs under the same condition. Through the result, we can find the fact that shotcrete and steel ribs do not work as one unit because of slipping on the boundary. Also, when numerical analyzing, it was concluded that steel ribs cover all bending moment and shotcrete and steel ribs share with axial force according to the compressive strength.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.42 no.6
• /
• pp.515-521
• /
• 2014

In this paper, we designed axis-displaced Gregorian antenna by using Ray-tracing method. This antenna improves gain, VSWR by rotating the axis of the sub-reflector to get rid of E-field wave returned from sub-reflector to feed horn. Therefore it reduce the sub-reflector size and the volume of antenna. This method is used to track the propagation path for radiation pattern of feed horn from feed horn to sub-reflector, main-reflector and air. We get E-field distribution of this antenna aperture and calculate antenna radiation pattern and optimize the antenna performance. The Ray-tracing Method was verified because the gain, radiation patterns, side lobe level, beam width and return loss of the designed antenna are very similar to CST simulation result and a measured result of the fabricated antenna.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2006.05a
• /
• pp.660-665
• /
• 2006

This paper presents a finite element method to analyze the free and forced vibration of a hard disk drive (HDD) considering the flexibility of a spinning disk-spindle with fluid dynamic bearings (FDBs), an actuator with pivot bearings, an air bearing between head-disk interface and the base with complicated geometry. Finite element equation of each component is consistently derived with the satisfaction of the geometric compatibility of the internal boundary between each component. The spinning disk, hub and FDBs are modeled by annular sector elements, beam elements and stiffness and damping elements, respectively. The actuator am, E-block, suspension and base plate are modeled by tetrahedral elements. The pivot bearing in the actuator and the air bearing between head-disk interfaces are modeled by the stiffness element with five degrees of freedom and the axial stiffness, respectively. A global matrix equation obtained by assembling the finite element equations of each substructure is transformed to a state-space matrix-vector equation, and both damped natural frequencies and modal damping ratios are calculated by solving the associated eigenvalue problem with the restarted Arnoldi iteration method. Modal and shock testing are performed to show that the proposed method well predicts the vibration characteristics of a HDD.

• Journal of the Optical Society of Korea
• /
• v.12 no.2
• /
• pp.98-102
• /
• 2008

Optical Coherence Tomography (OCT) is an important noninvasive medical imaging technique that can reveal subsurface structures of biological tissue. OCT has demonstrated a good correlation with histology in sufficient resolution to identify morphological changes in articular cartilage to differentiate normal through progressive stages of degenerative joint disease. Current OCT systems provide individual cross-sectional images that are representative of the tissue directly under the scanning beam, but they may not fully demonstrate the degree of degeneration occurring within a region of a joint surface. For a full understanding of the nature and degree of cartilage degeneration within a joint, multiple OCT images must be obtained and an overall assessment of the joint surmised from multiple individual images. This study presents frequency domain three-dimensional (3-D) OCT imaging of degenerative joint cartilage extracted from bovine knees. The 3-D OCT imaging of articular cartilage enables the assembly of 126 individual, adjacent, rapid scanned OCT images into a full 3-D image representation of the tissue scanned, or these may be viewed in a progression of successive individual two-dimensional (2-D) OCT images arranged in 3-D orientation. A fiber-based frequency domain OCT system that provides cross-sectional images was used to acquire 126 successive adjacent images for a sample volume of $6{\times}3.2{\times}2.5\;mm^3$. The axial resolution was $8\;{\mu}m$ in air. The 3-D OCT was able to demonstrate surface topography and subsurface disruption of articular cartilage consistent with the gross image as well as with histological cross-sections of the specimen. The 3-D OCT volumetric imaging of articular cartilage provides an enhanced appreciation and better understanding of regional degenerative joint disease than may be realized by individual 2-D OCT sectional images.

• Steel and Composite Structures
• /
• v.18 no.5
• /
• pp.1083-1101
• /
• 2015

Previous theoretical equations for the shear capacity of steel beam to concrete filled steel tube (CFT) column connections vary in the assumptions for the shear deformation mechanisms and adopt different equations for calculating shear strength of each component (steel tube webs, steel tube flanges, diaphragms, and concrete etc.); thus result in different equations for calculating shear strength of the joint. Besides, shear force-deformation relations of the joint, needed for estimating building drift, are not well developed at the present. This paper compares previously proposed equations for joint shear capacity, discusses the shear deformation mechanism of the joint, and suggests recommendations for obtaining more accurate predictions. Finite element analyses of internal diaphragm connections to CFT columns were carried out in ABAQUS. ABAQUS results and theoretical estimations of the shear capacities were then used to calibrate rotational springs in joint elements in OpenSEES simulating the shear deformation behavior of the joint. The ABAQUS and OpenSEES results were validated with experimental results available. Results show that: (1) shear deformation of the steel tube dominates the deformation of the joint; while the thickness of the diaphragms has a negligible effect; (2) in OpenSEES simulation, the joint behavior is highly dependent on the yielding strength given to the rotational spring; and (3) axial force ratio has a significant effect on the joint deformation of the specimen analyzed. Finally, modified joint shear force-deformation relations are proposed based on previous theory.

• Structural Engineering and Mechanics
• /
• v.39 no.2
• /
• pp.241-266
• /
• 2011

The Self Compacting Concrete, SCC is the new generation type of concrete which is not needed to be compacted by vibrator and it will be compacted by its own weight. Since SCC is a new innovation and also the high strength self compacting concrete, HSSCC behavior is like a brittle material, therefore, understanding the strength effect on the serviceability performance of reinforced self compacting concretes is critical. For this aim, first the normal and high strength self compacting concrete, NSSCC and HSSCC was designed. Then, the serviceability performance of reinforced connections consisting of NSSCC and HSSCC were investigated. Twelve reinforced concrete connections (L = 3 m, b = 0.15 m, h = 0.3 m) were simulated, by this concretes, the maximum and minimum reinforcement ratios ${\rho}$ and ${\rho}^{\prime}$ (percentage of tensile and compressive steel reinforcement) are in accordance with the provision of the ACI-05 for conventional RC structures. This study was limited to the case of bending without axial load, utilizing simple connections loaded at mid span through a stub (b = 0.15 m, h = 0.3 m, L = 0.3 m) to simulate a beam-column connection. During the test, concrete and steel strains, deflections and crack widths were measured at different locations along each member. Based on the experimental readings and observations, the cracked moment of inertia ($I_{cr}$) of members was determined and the results were compared with some selective theoretical methods. Also, the flexural crack widths of the members were measured and the applicability for conventional vibrated concrete, as for ACI, BS and CSA code, was verified for SCCs members tested. A comparison between two Codes (ACI and CSA) for the theoretical values cracking moment is indicate that, irrespective of the concrete strength, for the specimens reported, the prediction values of two codes are almost equale. The experimental cracked moment of inertia $(I_{cr})_{\exp}$ is lower than its theoretical $(I_{cr})_{th}$ values, and therefore theoretically it is overestimated. Also, a general conclusion is that, by increasing the percentage of ${\rho}$, the value of $I_{cr}$ is increased.

• Structural Engineering and Mechanics
• /
• v.40 no.1
• /
• pp.65-84
• /
• 2011

In this paper a simple mathematical model for approximate static analysis of combined system of framed tube, shear core and two outrigger-belt truss structures subjected to lateral loads is presented. In the proposed methodology, framed tube is modeled as a cantilevered beam with a box section and interaction between shear core and outrigger-belt truss system with framed tube is modeled using torsional springs placed at location of outrigger-belt truss; these torsional springs act in a direction opposite to rotation generated by lateral loads. The effect of shear lag on axial deformation in flange is quadratic and in web it is a cubic function of geometry. Here the total energy of the combined system is minimized with respect to lateral deflection and rotation in plane section. Solution of the resulting equilibrium equations yields the unknown coefficients of shear lag along with the stress and displacement distributions. The results of a numerical example, 50 storey building subjected to three different types of lateral loading obtained from SAP2000 are compared to those of the proposed method and the differences are found to be reasonable. The proposed method can be used during the preliminary design stages of a tall building and can provide a better understanding of the effects of various parameters on the overall structural behavior.