• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.455-460
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• 2002

In this study, a numerical analysis that can effectively predict the effect of strengthening of cracked flexural members is developed using axial deformation link elements. Concrete and interface between concrete and repair material are considered as quasi-brittle material. Reinforcing bars and reinforcing steel plates are assumed to perform as elasto-plastic materials. Unloading behavior of axial deformation link element is implemented. In the developed numerical model, a flexural member is intentionally cracked by pre-loading, then, the cracked member is repaired using extra elements, and reloaded. The results from analysis of repaired flexural members agrees well with available experiment results. Also, it was shown that the effect of strengthening and the change of failure mode with respect to the time for strengthening and thickness of repair materials. Based on the results, it was determined that the developed numerical model has a good agreement for determining failure modes and effect of strengthening in cracked flexural members. By utilizing the developed numerical analysis, the time and dimension of external strengthening in an existing cracked flexural member with predition of failure mechanism can be determined.

• Journal of the Korean Society of Safety
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• v.28 no.5
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• pp.21-26
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• 2013

Delamination of cover concrete due to re-bar corrosion is a critical damage reducing structural safety of reinforced concrete structures. Therefore, it should be detected and evaluated to provide appropriate maintenance to recover structural integrity. Impact-echo method, which utilizes thickness vibration characteristics of delaminated concrete section, is effective for detection and evaluation of small areal size delamination. However, it may not be applicable for large areal size delamination in which flexural vibration modes are dominated. In this study, applicability of vibration mode shapes of delaminated concrete section is investigated for visualization of delamination region in concrete structures. Numerical and experimental modal tests are performed to estimate mode shapes of delaminated concrete section and linear absolute summation technique is proposed for effective visualization of delamination region based on estimated mode shapes.

• 한국정보통신설비학회:학술대회논문집
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• 2007.08a
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• pp.419-422
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• 2007

This paper, designed UWB elliptical slot antenna and analysis based on the distribution of the electromagnetic fields pattern and resonant mode of designed antenna is presented. Designed antenna is fabricated on FR4 substrate with thickness of 1.524mm and relative dielectric constant 4.4. The measured bandwidth of $3.6GHz{\sim}20GHz$ for VSWR<2. Through the field pattern and resonant mode analysis that the slot antenna operates on a series of the multi-pole radiation based on TE modes matched to system impedance. And the perfect magnetic wall is along the axis of symmetry on the y-z plane. This result gives us an easier method to design the similar antennas, which is the impedance matching to the system impedance after once constructing a proper structure with a series of multi-mode resonances.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.49-53
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• 2001

Recently hydroforming process became a process which is increasingly applied in the automotive industry. As the hydroforming process is a new technology, there is no abundant data to assist manufacturing the products. To investigate the effects of process parameters on the tube hydroforming process, simple bulging, circular bulging and Tee-fitting tests are performed. The optimal leading path to escape the failure modes(bursting, wrinkling) is determined and the effects of the process parameters, the internal pressure and axial feeding on the product quality, such as thickness distribution, forming height and branch dome shape are investigated.

• Journal of the Korean Society of Safety
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• v.19 no.4 s.68
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• pp.101-108
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• 2004

In this study, open conical shells with ring and stringers are analyzed A versatile 4-node shell element which is useful for the analysis of conical shell structures is used and 3-D beam element is used for stiffeners. An improved flat shell element is established by the combined use of the addition of non-conforming displacement modes and the substitute shear strain fields. The proposed element has six degrees of freedom per node and permits an easy connection to other types(beam element) of finite elements. Optimum location and optimum section properties of ring and stinger are obtained. It is shown thai the thickness of conical shell can be reduced about $20\~50\%$ by appropriate location of stiffeners.

• Steel and Composite Structures
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• v.15 no.1
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• pp.41-55
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• 2013

This paper presents a numerical study of axially loaded concrete-filled steel tubular columns with "T" shaped cross section (CFTTS) based on the ABAQUS standard solver. Two types of columns with "T" shaped cross section, the common concrete-filled steel tubular columns with "T" shaped cross section (CCFTTS) and the double concrete-filled steel tubular columns with "T" shaped cross section (DCFTTS), are discussed. The failure modes, confining effects and load-displacement curves are analyzed. The numerical results indicate that both have the similar failure mode that the steel tubes are only outward buckling on all columns' faces. It is found that DCFTTS columns have higher axial capacities than CCFTTS ones duo to the steel tube of DCFTTS columns can plays more significant confining effect on concrete. A parametric study, including influence of tube thickness, concrete strength and friction coefficient of tube-concrete interface on the axial capacities is also carried out. Simplified formulae were also proposed based on this study.

• Journal of Welding and Joining
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• v.15 no.2
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• pp.64-71
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• 1997

In order to define the effects on shapes of welding joint, during Post Welding Heat Treatment (PWHT), we have carried out numerical analysis on the several test pieces by using computer program which was based on thermal-elasto-plastic-creep theories for the study. And then, welding residual stresses after PWHT were measured same test-pieces to compare with the results of numerical analysis. The main results obtained from this study is as follows: 1) The distribution modes of welding residual stresses are same on the all test pieces after and during PWHT by the both sides (measurement and numerical analysis). 2) The mechanical difference for change the thickness of plate and bevel angle are not appeared. 3) In a mechanical point of view (like material quality test, welding deformation etc.), manimum bevel angle (40$^{\circ}$.) is more suitable than maximum bevel angle (70$^{\circ}$).

• Journal of Magnetics
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• v.5 no.2
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• pp.35-39
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• 2000

The correlation between the activation volumes of wall-motion and nucleation processes in Co/Pd multilayers has been investigated. Each activation volume was estimated from the field dependence of the wall-motion speed and the nucleation rate, respectively, based on time-resolved domain patterns grabbed by a MOKE microscope system. Both the activation volumes are changed in the same manner around $0.2\sim1.1\times10^{-17}cm^3$ with changes in the multilayered structure. Interestingly, the correlation between the activation volumes is sensitive to the multilayered structure; the wall-motion activation volume is smaller than the nucleation activation volume for a sample having a smaller number of repeats and a thinner Co-layer thickness, and vice versa. The correlation is closely related with the contrasting reversal modes; the process having the smaller activation volume dominates.

• Computational Structural Engineering
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• v.8 no.2
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• pp.133-140
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• 1995

The buckling analysis of Glass Fiber Reinforced Plastic pipes was studied through a three dimentsional finite element method. In the finite element analysis, an improved degenerated shell element with incompatible modes and assumed shear strain fields are employed with 3 displacements and 2 rotations for each joints. Buckling analysis is carried out for various thicknesses and different fiber orientations. Finite element results show that the buckling load increases as the thickness does with the variation of coupling stiffness.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.234-237
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• 2006

A series of three shear wall specimens was tested under constant axial stress and reversed cyclic lateral loading in order to evaluate the seismic retrofit that had been proposed for the shear wall with the opening induced by remodeling. One of these specimens was tested in the as-built condition and the other two were retrofitted prior to testing. The retrofit involved the use of carbon fiber sheets and steel plates (thickness of 3mm) over the entire face of the wall. The test results show that the ultimate failure modes of the specimens were found to be shear fracture of the wall around the opening and two difference types of retrofitting strategy make the different effects of a rise in the strength of each specimen.