• Structural Engineering and Mechanics
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• v.39 no.4
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• pp.579-598
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• 2011

The present work mainly reports a significant development of a novel efficient meshfree method for vibration and buckling analysis of orthotropic plates. The plate theory with orthotropic materials is followed the Kirchhoff''s assumption in which the only deflection is field variable and approximated by the moving Kriging interpolation approach, a new technique used for constructing the shape functions. The moving Kriging technique holds the Kronecker delta property, thus it makes the method efficiently in imposing the essential boundary conditions and no special techniques are required. Assessment of numerical results is to accurately illustrate the applicability and the effectiveness of the proposed method in the class of eigenvalue problems.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.674-679
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• 1998

In designing the prestressed concrete box-bridge, the dead load, prestressing force, creep and shrinkage of concrete are the main factors which influence the camber and deflection of segmental concrete structure under construction. Among these factors the creep and shrinkage are the functions of the time-dependent property which, therefore, must be considered with time. The prediction model for estimating creep and shrinkage of concrete has been suggested by ACI, CEB/FIP, JSCE and KSCE design code and EMM, AEMM, RCM, IDM and SSM has been suggested for analytical method in consideration of the time-dependent characteristics. In this study, the creep test was carried out for four curing ages of concrete which were applied to the prestressed concrete structure at a construction site, and the results of test were compared to the values of creep prediction by the design code. Also the creep test of step-wise incremental stresses were performed and were compared to analytical methods.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.49 no.7
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• pp.462-467
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• 2000

In general, when geometry and current distribution have a periodic or symmetric property, the analysis of a part model is sufficient to represent that of a whole model by using the periodic boundary condition. It is impossible, however, to apply the periodic boundary condition when the current distribution is not symmetric even if the geometry of the model is symmetric. In this paper, a novel technique to resolve this problem is proposed. Even when the geometry is symmetric and the current distribution is not, the proposed method enables that calculation time for a whole model is reduced to that for a part model. The proposed method is applied to a deflection yoke (DY), and validness and efficiency of the method are verified.

• Journal of the Korea Concrete Institute
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• v.11 no.3
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• pp.23-34
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• 1999

In designing PSC box girder bridge, the dead load, prestressing force, creep and shrinkage of concrete are the main factors which influence the camber and deflection of segmental concrete structure under construction. Among these factors the creep and shrinkage are the functions of the time-dependent property which, therefore, must considered with time. The prediction model for estimating creep and shrinkage of concrete has been suggested by ACI, CEB/FIP, JSCE and KSCE design code. In this study the creep and shrinkage test were carried out for four curing ages of concrete which was applied to the pretressed concrete box-girder bridge at a construction site, and the results of test were compared to the values of prediction by the design code. Shrinkage test shows that the test results are similar to KSCE-96 and JSCE-96 but very higher than other prediction model and creep test results are generally similar to ACI-209 and DSCE-96 but lower than other prediction models in contrast to shrinkage test.

• KCI Concrete Journal
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• v.11 no.3
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• pp.99-107
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• 1999

In designing the Prestressed concrete box-girder bridge. dead load, prestressing force, creep and shrinkage of concrete are the main factors which influence the camber and deflection of segmental concrete structure under construction. Among these factors the creep and shrinkage are the functions of the time-dependent property which. therefore, must be considered with time. The prediction model for estimating creep and shrinkage of concrete has been suggested by ACI, CEB/FIP, JSCE and KSCE design code and EMM, AEMM, RCM, IDM and SSM has been suggested for analytical method in consideration of time-dependent characteristics. In this study the creep test was carried out for four different curing ages of concrete which were applied to the Prestressed concrete structure at the construction site, and the results of test were compared with the values of creep prediction proposed by the design code. Also the creep test was performed with step-wise incremental stresses and the results were compared to the analytical values.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.4
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• pp.231-236
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• 2004

A normally open thermopneumaticc-actuated microvalve has been fabricated and their properties are investigated. The advantages of the proposed microvalve are of the low cost fabrication process and the transparent optical property using polydimethylsiloxane (PDMS) and indium tin oxide (ITO) glass. The fabricated microvalves with in-channel configuration are easily integrated with other microfluidic devices on the same substrate. The fabrication process of thermopneumatic-actuated microvalvesusing PDMS is very simple and its performance is very suitable for a disposable lab-on-a-chip. The PDMS membrane deflection increases and the flow rates of the microchannel with microvalvels decrease as the applied power to the ITO heater increases. The powers at flow-off are dependent on the membrane thickness and the applied inlet pressure but are independent of the channel width of microvalves. The flow rate is well controlled by the switching function of ITO heater and the closing/opening times are around 20 sec and 25 sec, respectively.

• Journal of the Korean Ceramic Society
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• v.36 no.8
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• pp.799-804
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• 1999

Composites of SiC-Si3N4 consisted of uniformly distributed elongated $\beta$-Si3N4 grains and equiaxed $\beta$-SiC grains were fabricated with $\beta$-SiC,. $\alpha$-Si3N4 Al2O3 and Y2O3 powders. By hot-pressing and subsequent annelaing elongated $\beta$-Si3N4 grains were grown via$\alpha$longrightarrow$\beta$ phase transformation and equiaxed $\beta$-Si3N4 composites increased with increasing the Si3N4 content owing to the reduced defect size and enhanced crack deflection by elongated $\beta$-Si3N4 grains and the grain boundary strengthening by nitrogen incorporation. Typical flexural strength and fracture toughness of SiC-40 wt% Si3N4 composites were 783 MPa and 4.2 MPa.m1/2 respectively.

• Structural Engineering and Mechanics
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• v.51 no.5
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• pp.773-792
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• 2014

In this paper, we study the inverse mode shape problem for an Euler-Bernoulli beam, using an analytical approach. The mass and stiffness variations are determined for a beam, having various boundary conditions, which has a prescribed polynomial second mode shape with an internal node. It is found that physically feasible rectangular cross-section beams which satisfy the inverse problem exist for a variety of boundary conditions. The effect of the location of the internal node on the mass and stiffness variations and on the deflection of the beam is studied. The derived functions are used to verify the p-version finite element code, for the cantilever boundary condition. The paper also presents the bounds on the location of the internal node, for a valid mass and stiffness variation, for any given boundary condition. The derived property variations, corresponding to a given mode shape and boundary condition, also provides a simple closed-form solution for a class of non-uniform Euler-Bernoulli beams. These closed-form solutions can also be used to check optimization algorithms proposed for modal tailoring.

• Journal of Powder Materials
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• v.7 no.3
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• pp.149-153
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• 2000

In this study, the fabrication of $Al_2O_3$/5vol.%Cu nanocomposite and its mechanical property were discussed. The nanocomposite powders were produced by high energy ball milling of $Al_2O_3$ and Cu elemental powders. The ball-milled powders were sintered with Pulse Electric Current Sintering (PECS) facility. The relative densities of specimens sintered at $1200^{\circ}C$ and $1250^{\circ}C$ after soaking process at $900^{\circ}C$ were 96% and over 97%, respectively. The sintered microstructures were composed of $Al_2O_3$ matrix and the nano-sized Cu particles distributed on grain boundaries of $Al_2O_3$ matrix. The nanocomposite exhibited the enhanced fracture toughness compared with general monolithic $Al_2O_3$. The toughness increase was explained by the crack deflection and bridging by dispersed Cu particles.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.5
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• pp.41-50
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• 2014

This study evaluated the bonding property of fiber and flexural behavior of fiber reinforced concrete. Amorphous steel fiber, hooked steel fiber and polyamide fiber was used for evaluation of bonding property and flexural behavior. As a result, the hooked steel fiber was pulled out from matrix when peak stress. However amorphous steel fiber occurred shear failure because bonding strength between fiber and matrix was higher than tensile strength of fiber. Polyamide fibers occurred significantly displacement to peak stress because of elongation of fiber. After that peak stress, fiber was cut off. Amorphous steel fiber reinforced concrete had a greater maximum flexural load compared with hooked steel fiber reinforced concrete because bonding performance between fiber and matrix was high and mixed population of fiber was many. However flexural stress was rapidly reduced in load-deflection curve because of shear failure of fiber. Flexural stress of hooked steel fiber reinforced concrete was slowly reduced because fiber was pulled out from the matrix. In the case of polyamide fiber reinforced concrete, flexural stress was rapidly lowered because of elongation of fiber. However flexural stress was increased again because of bonding property between polyamide fiber and matrix. The pull-out properties of the fiber and matrix has effect on the deformation capacity and flexural strength of fiber reinforced concrete.