• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.1
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• pp.1-8
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• 1999

Dynamic elastoplastic LPM (lumped parameter mass) analyses are carried out in order to investigate the seismic resistant performance of a typical high-rise shear wall apartment subjected to several earthquakes. Three-dimensional nonlinear pushover analysis is adopted to estimate initial elastic stiffness, yielding strength and post-yielding stiffness of each story for the time history analysis of LPM shear model. For the hysteresis of each story, Clough and bilinear models are used with the input of four recorded earthquake ground motions of EI Centro 1940 NS, Taft 1952 EW, Hachinohe 1968 NS and Kobe 1995 NS, of which the amplitudes are scaled down to have the same maximum ground velocity of 12 kine. The result shows that yieldings take place in most storys of the building, i.e. the earthquake resistant capacity of this high-rise shear wall apartment is not sufficient at the event of earthquake M=5~6.

• Nuclear Engineering and Technology
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• v.52 no.6
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• pp.1297-1303
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• 2020

In this study, nuclear radiation shielding and rigidity parameters of Y (0.1-x)B0.6Bi1.8O3La2x glassy system were investigated in order to determine it's suitability for use as nuclear radiation shielding materials. Therefore, a group of bismuth borate glass samples with La₂O₃ additive were synthesized using the technique of melt quenching. According to the results, the increase of the La₂O₃ additive increases the density of the glass samples and the mass attenuation coefficient (μ_m) values, whereas the half-value layer (HVL) and mean free path (MFP) values decrease. The effective atomic number (Z_eff) is also enhanced with an increment of both mass removal cross section for neutron (Σ_R) and absorption neutron scattering cross section (σ_abs). In addition to the other parameters, rigidity parameter values were theoretically examined. The increase of La₂O₃ causes some other important magnitudes to increase. These are the average crosslink density, the number of bonds per unit volume, as well as the stretching force constant values of these glass samples. These results are in concordance with the increase of elastic moduli in terms of the Makishima-Mackenzie model. This model showed an increase in the rigidity of the glass samples as a function of La₂O₃.

• Korea-Australia Rheology Journal
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• v.21 no.4
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• pp.213-223
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• 2009

Taylor-Couette flow (i.e., flow between concentric, rotating cylinders) has long served as a paradigm for studies of hydrodynamic stability. For Newtonian fluids, the rich cascade of transitions from laminar, Couette flow to turbulent flow occurs through a set of well-characterized flow states (Taylor Vortex Flow, wavy Taylor vortices, modulated wavy vortices, etc.) that depend on the Reynolds numbers of both the inner and outer cylinders ($Re_i$ and $Re_o$). While extensive work has been done on (a) the effects of weak viscoelasticity on the first few transitions for $Re_o=0$ and (b) the effects of strong viscoelasticity in the limit of vanishing inertia ($Re_i$ and $Re_o$ both vanishing), the viscoelastic Taylor-Couette problem presents an enormous parameter space, much of which remains completely unexplored. Here we describe our recent experimental efforts to examine the effects of drag reducing polymers on the complete range of flow states observed in the Taylor-Couette problem. Of particular importance in the present work is 1) the rheological characterization of the test solutions via both shear and extensional (CaBER) rheometry, 2) the wide range of parameters examined, including $Re_i$, $Re_o$ and Elasticity number E1, and 3) the use of a consistent, conservative protocol for accessing flow states. We hope that by examining the stability changes for each flow state, we may gain insights into the importance of particular coherent structures in drag reduction, identify simple ways of screening new drag reducing additives, and improve our understanding of the mechanism of drag reduction.

• Journal of the Korea Concrete Institute
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• v.28 no.2
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• pp.213-221
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• 2016

Uniaxial compression tests for ultra-high performance hybrid steel fiber reinforced concrete (UHPC) were performed to evaluate the compressive behavior of UHPC. The UHPC for testing contains hybrid steel fibers with a predetermined ratio using a length of 19 mm and 16 mm straight typed steel fibers. Test parameter was determined as a fiber volume ratio to investigate the effect of fiber volume ratio on the strength and secant modulus of elasticity. Test results showed that the compressive strength and elastic modulus of UHPC increased with increasing the fiber volume ratio. Based on the test results, the compressive strength and modulus of elasticity equations were proposed as function of the compressive strength of unreinforced and fiber reinforced UHPC, respectively. The simplified equations for predicting the mechanical properties of the UHPC were a good agreement with the test data. The proposed equations are expected to be applied to the SFRC and UHPC with steel fibers.

• Journal of the Korean GEO-environmental Society
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• v.18 no.5
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• pp.17-26
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• 2017

Tunnel excavation in jointed rock mass induces a displacement along tunnel excavation line and its assessment is very important to ensure the stability of tunnel and a demanded space. Tunnel displacement is directly related to the deformation modulus of ground and therefore it is essential to know the value of the parameter. However, most rock masses where tunnels are constructed are generally jointed and it is difficult to find out the deformation modulus of jointed rock mass simply based on an homogeneous isotropic elastic medium because the deformation modulus is highly affected by joint condition as well as rock type. Accordingly, this study carried out extensive numerical parametric studies to examine the variation of deformation modulus in different joint conditions and rock types under the condition of tunnel excavation. The study results were compared with existing empirical relationships and also shown in the chart of deformation modulus variation in different jointed rock mass conditions.

• Journal of the Korean Geotechnical Society
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• v.19 no.1
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• pp.151-161
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• 2003

In this study, an interpretation method is proposed to evaluate the stress conditions, including individual excess pore pressure components ($\Delta{u}_{oct}$/ and $\Delta{u}_{shear}$), of normally consolidated clay elements adjacent to the cone face. It is assumed that the stress path of triaxial compression is representative f3r that of the soil element and the soil is elastic-perfectly plastic material. The proposed method is applied to the results of miniature piezocone tests conducted at Louisiana State University calibration chamber system. Based on the results of interpretation, it was found that the ratio of $\Delta{u}_{oct}$/ $\Delta{u}$and $\Delta{u}_{shear}$/$\Delta{u}$ estimated by the proposed method is affected only by the pore pressure parameter. The proposed method gives consistent and reliable values of $\Delta{u}_{oct}$/ $\Delta{u}$and $\Delta{u}_{shear}$/$\Delta{u}$ compared with early works, whereas those obtained by other solutions are significantly dependent on the accuracy in estimating soil properties such as undrained shear strength and rigidity index.

• Journal of the Korea Concrete Institute
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• v.19 no.4
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• pp.441-448
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• 2007

The beam-column assembly in a ductile reinforced concrete (RC) frames subjected to seismic loading are generally controlled by shear and bond mechanisms, both of which exhibit poor hysteretic properties. Hence the response of joints is restricted essentially to the elastic domain. The usual earthquake resistant design philosophy of ductile frame buildings allows the beams to form plastic hinges adjacent to beam-column assembly. Increased strain in these plastic hinge regions affect on joint strain to be increased. Thus bond and shear joint strength are decreased. The research reported in this paper presents the test results of five RC beam-column assembly after developing plastic hinges in beams. Main parameter of the test Joints was the amount of the longitudinal tensile reinforcement of the beams. Test results indicted that the ductile capacity of joints increased as the longitudinal tensile reinforcement of the beams decreased. In addition, both the tensile strain of the longitudinal reinforcement bars in the joint and the ductile ratio of the beam-column assemblages increased due to the yielding of steel bars in the plastic hinge regions.

• Journal of the Korea Concrete Institute
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• v.20 no.3
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• pp.357-367
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• 2008

Parametric study of beams with reinforced with FRP rebar is conducted in this study. Using ABAQUS program, the finite element analysis model is set and calibrated with the experimental results which have been conducted by the authors. The employed design parameters are reinforcement ratio, elastic modulus of rebar, and concrete strength. The obtained results from FE analysis are investigated in terms of normalized beam stiffness. In particular, the effect of reinforcement ratio on the flexural stiffness is investigated with comparing with the model code specified on ACI 440. From the analysis results, the reinforcement ratio in beam is the first parameter affecting on the beam stiffness. In addition, its effect could be increased with higher concrete strength.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.3 s.174
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• pp.777-785
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• 2000

The low-cycle fatigue behaviors of cast AI-Si alloy and composite with reinforcement of SIC particles were compared with those of extruded unreinforced matrix alloy and composite in order to investigate the influence of cast and extrusion processes on the cyclic deformation and fatigue life. Generally, both cast and extruded composites including the unreinforced alloy exhibited cyclic hardening behaviour, with more pronounced strain-hardening for the composites with a higher volume fraction of the SiC particles. However, cast composite under a low applied cyclic strain showing no observable plastic strain exhibited cyclic softening behavior due to the cast porosities. The elastic modulus and yield strength of the cast composite were found to be quite comparable to those of the extruded composite, however, the extrusion process considerably improved the ductility and fracture strength of the composite by effectively eliminating the cast porosities. Low-cycle fatigue lives of the cast alloy and composite were shorter than those of the extruded counterparts. Large difference in life between cast and extruded composites was attributed to the higher influence of the cast porosities on the fatigue life of the composite than that of the unreinforced alloy material. A fatigue damage parameter using strain energy density effectively represented the inferior life in the low-cycle regime and superior life in the high-cycle regime for the composite, compared to the unreinforced alloy.

• Structural Engineering and Mechanics
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• v.58 no.1
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• pp.59-91
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• 2016

Laminated composite shells are commonly used in various engineering applications including aerospace and marine structures. In this paper, using semi-analytical finite strip method, the buckling behavior of laminated composite deep as well as thick shells of revolution under follower forces which remain normal to the shell is investigated. The stiffness caused by pressure is calculated for the follower forces subjected to external fibers in thick shells. The shell is divided into several closed strips with alignment of their nodal lines in the circumferential direction. The governing equations are derived based on first-order shear deformation theory which accounts for through thickness-shear flexibility. Displacements and rotations in the middle surface of shell are approximated by combining polynomial functions in the meridional direction as well as truncated Fourier series with an appropriate number of harmonic terms in the circumferential direction. The load stiffness matrix which accounts for variation of loads direction will be derived for each strip of the shell. Assembling of these matrices results in global load stiffness matrix which may be un-symmetric. Upon forming linear elastic stiffness matrix called constitutive stiffness matrix, geometric stiffness matrix and load stiffness matrix, the required elements for the second step analysis which is an eigenvalue problem are provided. In this study, different parameter effects are investigated including shell geometry, material properties, and different boundary conditions. Afterwards, the outcomes are compared with other researches. By considering the results of this article, it can be concluded that the deformation-dependent pressure assumption can entail to decrease the calculated buckling load in shells. This characteristic is studied for different examples.