• Journal of the Korean Geotechnical Society
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• v.28 no.4
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• pp.35-42
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• 2012

This paper evaluates the effect of anisotropic conductivity on the seepage face and reliability index of an homogeneous dam with and without toe drain. The analysis are conducted under steady state saturated-unsaturated seepage condition using finite element method. Various anisotropic conductivity ratios were interpreted under such conditions as the vertical conductivity is reduced while the horizon conductivity is fixed. The shear strength of soil is defined by the modified Mohr-Coulomb failure criterion. The analysis results demonstrate that the length of seepage face and reliability index at the downstream and upstream of the dam increase with an increasing anisotropic ratio. These results of the seepage face and reliability index, however, depend on the total head difference between the upstream slope and downstream toe. The difference in seepage face and reliability index is attributed to the different equipotential head with different anisotropic ratios of the dam material.

• Advances in concrete construction
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• v.12 no.5
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• pp.377-389
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• 2021

Reinforced concrete vertical silos are universal structures that store large amounts of granular materials. Due to the asymmetric structure, heavy load, uneven storage material distribution, and the difference between the storage volume and the storage material bulk density, the corresponding earthquake is very complicated. Some scholars have proposed the calculation method of horizontal forces on reinforced concrete vertical silos under the action of earthquakes. Without considering the effect of torsional effect, this article aims to reveal the expansion factor of the silo group considering the torsional effect through experiments. Through two-way seismic simulation shaking table tests on reinforced concrete column-supported group silo structures, the basic dynamic characteristics of the structure under earthquake are obtained. Taking into account the torsional response, the structure has three types of storage: empty, half and full. A comprehensive analysis of the internal force conditions under the material conditions shows that: the different positions of the group bin model are different, the side bin displacement produces a displacement difference, and a torsional effect occurs; as the mass of the material increases, the structure's natural vibration frequency decreases and the damping ratio Increase; it shows that the storage material plays a role in reducing energy consumption of the model structure, and the contribution value is related to the stiffness difference in different directions of the model itself, providing data reference for other researchers; analyzing and calculating the model stiffness and calculating the internal force of the earthquake. As the horizontal side shift increases in the later period, the torsional effect of the group silo increases, and the shear force at the bottom of the column increases. It is recommended to consider the effect of the torsional effect, and the increase factor of the torsional effect is about 1.15. It can provide a reference for the structural safety design of column-supported silos.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.4
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• pp.334-341
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• 2003

When the pressure tubes(f are in contact with the calandria tube(CT) in the pressurized heavy water reactor(PHWR), the temperature difference between inner and outer wall of W results in a thermal diffusion of hydrogen (deuterium) and hydride blisters are formed on the outer surface of PT. Because the hydride blisters and zirconium matrix are acoustically continuous, it is not easy to distinguish the blisters from the matrix with conventional ultrasonic method. An ultrasonic velocity ratio method was developed to detect small hydride blisters on the zirconium pressure tube. Hydride blisters were grown in the PT specimen using a steady state thermal diffusion device. The flight times of longitudinal echo and reflected shear echo from the outer surface were measured accurately. The velocity ratio of the longitudinal wave to the shear wave was calculated and displayed using contour plot. Compared to the conventional flight time method of longitudinal wave, the velocity ratio method shows superior sensitivity to detect smaller blisters as well as better images for the blister shapes. Detectable limit of the outer shape of the hydride blisters was conservatively estimated as $500{\mu}m$, with the same specifications of ultrasonic transducer used in the actual PHWR pressure tube inspection.

• Journal of the Korean Society for Nondestructive Testing
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• v.15 no.2
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• pp.378-385
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• 1995

The ultrasonic non-destructive testing uses the directivity of the ultrasonic pulse wave which propagates in one direction. The directivity is expressed as the relationship between the propagate direction and its sound pressure. The directivity of ultrasonic wave is closely related to determination of probe arrangement, testing sensitivity, scanning pitch and defect location and characterization. The paper measured the directivity of shear wave, which reflected from artificial defect located in weld metal zone in butt welded joint similar model made of pyrex glass by using visualization method. 2 MHz and 4 MHz angle probes were used to measure the directivity of reflection wave at the artificial defect. The directivity of shear waves reflected from the defect was different according to the probe position and the shape of butt welded joint. The difference of directivity of reflection wave was existed between 2 MHz and 4 MHz angle probes. The angle of reflection wave became equal to angle of incidence as increase of the height of excess metal.

• The korean journal of orthodontics
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• v.41 no.1
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• pp.51-58
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• 2011

Objective: To evaluate the shear bond strength (SBS), fracture mode, wire pull out (WPO) resistance and microleakage between low-shrinking and conventional composites used as a lingual retainer adhesive. Methods: A total of 120 human mandibular incisor teeth, extracted for periodontal reasons, were collected. Sixty of them were separated into two groups. To determine the SBS, either Transbond-LR (3M-Unitek) or Silorane (3M-Espe) was applied to the lingual surface of the teeth by packing the material into standard cylindrical plastic matrices (Ultradent) to simulate the lingual retainer bonding area. To test WPO resistance, 20 samples were prepared for each composite where the wire was embedded in the composite materialand cured. Then tensile stress was applied until failure of the composite occurred. The remaining 60 teeth were divided into two groups and multi-stranded 0.0215-inch diameter wire was bonded with the same composites. Microleakage was evaluated by the dye penetration method. Statistical analyses were performed by Wilcoxon, Pearson chi-square, and Mann-Whitney-U tests at p < 0.05 level. Results: The SBS and WPO results were not statistically significant between the two groups. Significant differences were found between the groups in terms of fracture mode (p < 0.001). Greater percentages of the fractures showed mix type failure (85%) for Silorane and adhesive (60%) for Transbond-LR. Microleakage values were lower in low-shrinking composite than the control and this difference was found to be statistically significant (p < 0.001). Conclusions: Low-shrinking composite produced sufficient SBS, WPO and microleakage values on the etched enamel surfaces, when used as a lingual retainer composite.

• Korean Journal of Applied Biomechanics
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• v.28 no.3
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• pp.175-180
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• 2018

Objective: Anterior cruciate ligament reconstruction (ACLR) has been considered the primary treatment for anterior cruciate ligament (ACL) injured patient. However, there is little biomechanical evidence regarding bilateral knee joint biomechanics during landing and cutting task after ACLR. Method: Eighteen females with ACLR participated in this investigation. Double leg jump landing (DLJL) and single leg jump cut (SLJC) biomechanics were assessed. Results: During DLJL, the healthy knee showed greater knee valgus angle at initial contact ($^{\circ}$) compared to the injured knee (Injured: $2.93{\pm}2.59$, Healthy: $4.20{\pm}2.46$, t=2.957, p=0.009). There was a significant difference in anterior tibial shear force ($N{\times}N^{-1}$) with greater in the injured knee (Injured: $1.41{\pm}0.39$, Healthy: $1.30{\pm}0.35$, t=2.201, p=0.042). During SLJC, injured knee showed greater knee extension moment ($N^*m{\times}[N^*m]^{-1}$) compared to healthy knee (Injured: $0.51{\pm}0.19$, Healthy: $0.47{\pm}0.17$, t=2.761, p=0.013). However, there was no significant differences between the knees in the other variables. Conclusion: ACLRfemales exhibited a greater knee valgus angle at initial contact and lesser anterior tibial shear force on the healthy knee during double leg jump landing. In addition, ACLR females showed a greater knee extension moment on the injured knee during single leg jump cut.

• Journal of the Korean GEO-environmental Society
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• v.15 no.5
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• pp.57-65
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• 2014

For economic and technical reasons, it is difficult to obtain high quality undisturbed cohesionless samples, hence most researchers rely on preparing remolded and reconstituted representative samples of sandy soils. In this study, moist tamping, air pluviation, and dry deposition methods were applied to make remolded samples at similar relative densities. A series of isotropically consolidated drained tests were conducted with accompanied by measured elastic wave velocities in order to evaluate a difference between sample preparation methods and relative densities. For the elastic wave velocity measurements, piezoelectric elements were installed on the top and bottom cap of the triaxial device. The results showed that soil behavior relies on sample preparation methods, and that the trend of shear wave velocity was the same with volumetric strain behavior.

• Korean Journal of Applied Biomechanics
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• v.28 no.4
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• pp.199-205
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• 2018

Objective: The purpose of this study was to examine the effect of increase in barbell weight on closely related variable to the anterior cruciate ligament (ACL) injury which are knee joint kinematics, joint load, joint moment, and maximum load attainment point during snatch of the weight lifting. Method: The subjects of the study were 10 male Korean national weight lifting athletes (69 kg 5, 77 kg 5; age: $21.80{\pm}3.91yrs.$, height: $168.00{\pm}4.06cm$, weight: $75.00{\pm}4.02kg$, career: $7.8{\pm}3.99yrs.$, snatch records: $168{\pm}4.06kg$). The weight of the barbell during the snatch operation was set at 70%, 75% and 80% of the highest records for each subject studied. Results: The result obtained from the one-way repeated measure ANOVA are as follows: With increased barbell weight, the extension moment of the left knee joint was higher in the 80% condition than the 70% (p<.001). However, other variables were not statistically significant difference. According to the factor analysis of the variables related to maximum load attainment point of the ACL major injury variables, the first sub-factor was the internal shear force, the posterior shear force, the abduction moment, and the muscle activity of the VL. The second sub-factor was the extension moment of the knee joint, compressive force, adduction moment, and the third sub-factor was the muscle activity of BF. Conclusion: These results indicate that the possibility of ACL injury can be lowered when performing a stable snatch movement.

• Steel and Composite Structures
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• v.43 no.5
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• pp.581-601
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• 2022

The main objective of this research work is to investigate the free vibration behavior of annular sandwich plates resting on the Kerr foundation at thermal conditions. This sandwich configuration is composed of two FGM face sheets as coating layer and a porous GPLRC (GPL reinforced composite) core. It is supposed that the GPL nanofillers and the porosity coefficient vary continuously along the core thickness direction. To model closed-cell FG porous material reinforced with GPLs, Halpin-Tsai micromechanical modeling in conjunction with Gaussian-Random field scheme is used, while the Poisson's ratio and density are computed by the rule of mixtures. Besides, the material properties of two FGM face sheets change continuously through the thickness according to the power-law distribution. To capture fundamental frequencies of the annular sandwich plate resting on the Kerr foundation in a thermal environment, the analysis procedure is with the aid of Reddy's shear-deformation plate theory based high-order shear deformation plate theory (HSDT) to derive and solve the equations of motion and boundary conditions. The governing equations together with related boundary conditions are discretized using the generalized differential quadrature (GDQ) method in the spatial domain. Numerical results are compared with those published in the literature to examine the accuracy and validity of the present approach. A parametric solution for temperature variation across the thickness of the sandwich plate is employed taking into account the thermal conductivity, the inhomogeneity parameter, and the sandwich schemes. The numerical results indicate the influence of volume fraction index, GPLs volume fraction, porosity coefficient, three independent coefficients of Kerr elastic foundation, and temperature difference on the free vibration behavior of annular sandwich plate. This study provides essential information to engineers seeking innovative ways to promote composite structures in a practical way.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1C
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• pp.33-39
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• 2009

Vertical soil stress near a pile subjected to negative skin friction (NSF) may be reduced due to shear transfer at the pile-soil interface. A three-dimensional finite difference analysis has been performed to clarify the influence of vertical and horizontal stress reductions on the pile behavour. In addition, a simple equation has been proposed to estimate vertical stress reduction of the soil near the pile. The vertical and horizontal stresses are reduced by substantial amount compared to corresponding stress components at the Greenfield condition. The horizontal extent of vertical stress reduction of the soil near the pile is rather limited to about up to 4-8 D, where D is the pile diameter. The findings from the current research indicate that widely used $\beta$-method may result in over-estimation of dragload (compressive force on piles due to NSF) and hence stress reduction needs to be incorporated in the original equation.