• Magazine of the Korea Concrete Institute
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• v.3 no.3
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• pp.149-157
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• 1991

This paper concentrates on the nonlinear analysis of the reinforced concrete flexural members under cyclic loading. To develop a nonlinear material model, concrete is treated as an orthotropic nonlinear material and steel is modeled as an elasto-plastic material. The models for hysteresis behavior with stiffness degradation in compression and for crack opening and closing in tension are included. The finite element computer program for the nonlinear analysis of RC flexural members under cyclic loading is developed. The accuracy and reliabihty of the numerical procedure IS demonstrated by the FEM analysis and test results of underreinforced concrete beams.

• Steel and Composite Structures
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• v.7 no.4
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• pp.279-301
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• 2007

When coupling beams are proportioned appropriately in coupled core wall (CCW) systems, the input energy from ground motions is dissipated primarily through inelastic deformations in plastic hinge regions at the ends of the coupling beams. It is desirable that the plastic hinges form at the beam ends while the base wall piers remain elastic. The strength and stiffness of the coupling beams are, therefore, crucial if the desired global behavior of the CCW system is to be achieved. This paper presents the results of nonlinear response history analysis of two 20-story CCW buildings. Both buildings have the same geometric dimensions, and the components of the buildings are designed based on the equivalent lateral force procedure. However, one building is fitted with steel coupling beams while the other is fitted with diagonally reinforced concrete coupling beams. The force-deflection relationships of both beams are based on experimental data, while the moment-curvature and axial load-moment relationships of the wall piers are analytically generated from cross-sectional fiber analyses. Using the aforementioned beam and wall properties, nonlinear response history analyses are performed. Superiority of the steel coupling beams is demonstrated through detailed evaluations of local and global responses computed for a number of recorded and artificially generated ground motions.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.1924-1926
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• 2005

Poly(methyl methacrylate) (PMMA) is one of the promising representive of polymer gate dielectric for its high resistivity and sutible dielectric constant. PMMA (Mw=96700) films were prepared on p-Si by spin coating method. PMMA were coated compactively and flatly as observes by AFM. MIS(Al/PMMA/p-Si) structure was made and capacitance-voltage (C-V) and current-voltage (I-V) measurements were done with PMMA films for repeated annealing cycles at $100^{\circ}C$. 1-V measured at various delay times $(0{\sim}20sec)$ showed little change and the absence of hysteresis in the I-V characteristics with delay times, which eliminate the possibility of deep traps in the PMMA films. The observed thermal stability, smooth surfaces, dielectric constant, I-V behavior implies PMMA formed by spin coating can be used as an efficient gate dielectric layer in OTFTs.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.366-367
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• 2006

Different orientated SBN thin films were deposited by Ion Beam Sputtering, and electric properties were measured on each orientation. Ferroelectric $Sr_xBa_{1-x}Nb_2O_6$(SBN) has excellent electro-optic, photo-refractive, piezoelectric, pyroelectric properties. SBN thin film has been deposited by various method, of sol-gel, PLD, CVD, sputtering, etc.. To avoid lead pollution of Pb-system perovskite ferroelectric materials. SBN thin films were fabricated for pyroelectric IR sensor. Using the ceramic target of the same composition and Pt(100)/$TiO_2/SiO-2$/Si(100) substrate, crystallization and orientation behavior as well as electric properties of the films were examined. Seed layer and thin films thickness was controlled to observe the effect on preferred orientation. We measured I-V, C-V, P-E hysteresis to characterize electric-properties on each orientations.

• Smart Structures and Systems
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• v.19 no.1
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• pp.57-66
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• 2017

Nanocomposites reinforced with carbon nanotube fibers exhibit greater stiffness, strength and damping properties in comparison to conventional composites reinforced with carbon/glass fibers. Consequently, most of the nanocomposite research is focused in understanding the dynamic characteristics, which are highly useful in applications such as vibration control and energy harvesting. It has been observed that those nanocomposites show better stiffness when the geometry of nanotubes is straight as compared to curvilinear although nanotube agglomeration may exist. In this work the damping behavior of the nanocomposite is characterized in terms of loss factor under the presence of nanotube agglomerations. A micro stick-slip damping model is used to compute the damping properties of the nanocomposites with multiwall carbon nanotubes. The present formulation considers the slippage between the interface of the matrix and the nanotubes as well as the slippage between the interlayers in the nanotubes. The nanotube agglomerations model is also presented. Results are computed based on the loss factor expressed in terms of strain amplitude and nanotube agglomerations. The results show that although-among the various factors such as the material properties (moduli of nanotubes and polymer matrix) and the geometric properties (number of nanotubes, volume fraction of nanotubes, and critical interfacial shear stresses), the agglomeration of nanotubes significantly influences the damping properties of the nanocomposites. Therefore the full potential of nanocomposites to be used for damping applications needs to be analyzed under the influence of nanotube agglomerations.

• Earthquakes and Structures
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• v.17 no.5
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• pp.463-475
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• 2019

In this paper, a procedure to develop fragility curves of structures equipped with semi-active tuned mass dampers (SATMDs) considering multiple failure criteria has been presented while accounting for the uncertainties of the input excitation, structure and control device parameters. In this procedure, Latin hypercube sampling (LHS) method has been employed to generate 30 random SATMD-structure systems and nonlinear incremental dynamic analysis (IDA) has been conducted under 20 earthquakes to determine the structural responses, where failure probabilities in each intensity level have been evaluated using Monte Carlo simulation (MCS) method. For numerical analysis, an eight-story nonlinear shear building frame with bilinear hysteresis material behavior has been used. Fragility curves for the structure equipped with optimal SATMDs have been developed considering single and multiple failure criteria for different performance levels and compared with that of uncontrolled structure as well as structure controlled using passive tuned mass damper (TMD). Numerical analysis has shown the capability of SATMDs in significant enhancement of the seismic fragility of the nonlinear structure. Also, considering multiple failure criteria has led to increasing the fragility of the structure. Moreover, it is observed that the influence of the uncertainty of input excitation with respect to the other uncertainties is considerable.

• Journal of Magnetics
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• v.16 no.1
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• pp.15-18
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• 2011

We have studied the $TiO_2$ doping effects on the flux pinning behavior of an $MgB_2$ superconductor synthesized by the in-situ solid-state reaction. From the field-cooled and zero-field-cooled temperature dependences of magnetization, the reversible-irreversible transition of $TiO_2$-doped $MgB_2$ was determined in the H-T diagram (the temperature dependence of upper critical magnetic field and irreversibility line). For comparison, the similar measurements are also obtained from SiC-doped $MgB_2$. The critical current density was estimated from the width of hysteresis loops in the framework of Bean's model at different temperatures. The obtained results manifest that nano-scale $TiO_2$ inclusions served as effective pinning centers and lead to the enhanced upper critical field and critical current density. It was concluded that the grain boundary pinning mechanism was realized in a $TiO_2$-doped $MgB_2$ superconductor.

• Earthquakes and Structures
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• v.13 no.2
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• pp.177-191
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• 2017

In the present study, exterior beam column sub-assemblages are designed in accordance with the codal stipulations prevailed at different times prior to the introduction of modern seismic provisions, viz., i) Gravity load designed with straight bar anchorage (SP1), ii) Gravity load designed with compression anchorage (SP1-D), iii) designed for seismic load but not detailed for ductility (SP2), and iv) designed for seismic load and detailed for ductility (SP3). Comparative seismic performance of these exterior beam-column sub-assemblages are evaluated through experimental investigations carried out under repeated reverse cyclic loading. Seismic performance parameters like load-displacement hysteresis behavior, energy dissipation, strength and stiffness degradation, and joint shear deformation of the specimens are evaluated. It is found from the experimental studies that with the evolution of the design methods, from gravity load designed to non-ductile and then to ductile detailed specimens, a marked improvement in damage resilience is observed. The gravity load designed specimens SP1 and SP1-D respectively dissipated only one-tenth and one-sixth of the energy dissipated by SP3. The specimen SP3 showcased tremendous improvement in the energy dissipation capacity of nearly 2.56 times that of SP2. Irrespective of the level of design and detailing, energy dissipation is finally manifested through the damage in the joint region. The present study underlines the seismic deficiency of beam-column sub-assemblages of different design evolutions and highlights the need for their strengthening/retrofit to make them fit for seismic event.

• Structural Engineering and Mechanics
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• v.71 no.1
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• pp.45-56
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• 2019

A modified mechanical model of pre-pressed spring self-centering energy dissipation (PS-SCED) brace is proposed, and the hysteresis band is distinguished by the indication of relevant state variables. The MDOF frame system equipped with the braces is formulated in an incremental form of linear acceleration method. A multi-objective genetic algorithm (GA) based brace parameter optimization method is developed to obtain an optimal solution from the primary design scheme. Parameter sensitivities derived by the direct differentiation method are used to modify the change rate of parameters in the GA operator. A case study is conducted on a steel braced frame to illustrate the effect of brace parameters on node displacements, and validate the feasibility of the modified mechanical model. The optimization results and computational process information are compared among three cases of different strategies of parameter change as well. The accuracy is also verified by the calculation results of finite element model. This work can help the applications of PS-SCED brace optimization related to parameter sensitivity, and fulfill the systematic design procedure of PS-SCED brace-structure system with completed and prospective consequences.

• Electronic Materials Letters
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• v.14 no.6
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• pp.749-754
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• 2018

Previous studies have reported on the mechanical robustness and chemical stability of flexible amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) on plastic substrates both in flat and curved states. In this study, we investigate how the polyimide (PI) substrate affects hydrogen concentration in the a-IGZO layer, which subsequently influences the device performance and stability under bias-temperature-stress. Hydrogen increases the carrier concentration in the active layer, but it also electrically deactivates intrinsic defects depending on its concentration. The influence of hydrogen varies between the TFTs fabricated on a glass substrate to those on a PI substrate. Hydrogen concentration is 5% lower in devices on a PI substrate after annealing, which increases the hysteresis characteristics from 0.22 to 0.55 V and also the threshold voltage shift under positive bias temperature stress by 2 ${\times}$ compared to the devices on a glass substrate. Hence, the analysis and control of hydrogen flux is crucial to maintaining good device performance and stability of a-IGZO TFTs.