• Journal of the Korean Geotechnical Society
• /
• v.38 no.10
• /
• pp.31-40
• /
• 2022

This study compares elastic moduli calculated using two stiffness testing methods with different strain ranges to evaluate the stress-settlement characteristics of foundation support layers. Elastic moduli were calculated by the soil stiffness gauge (SSG) in the micro-strain range and the plate load test (PLT) in the medium strain range. To apply the elastic moduli obtained by the two testing methods with different strain ranges to the design and construction of foundation soils, the correlation between each measurement value should be identified in advance. As a result of the comparative analysis of the elastic moduli calculated using the two methods in weathered soil and rock, which are representative support layers in Korea, the calculated elastic moduli differed depending on the types of soil and stress conditions. For various soil types, the static elastic modulus obtained by the PLT was reduced by 56% because of the difference in the strain level of the test compared with the dynamic elastic modulus obtained by the SSG. Therefore, the results show that it is necessary to apply corrections to the stress distribution, stress level, and dynamic effect according to the ground stiffness to effectively use the SSG instead of the PLT.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.11 no.4
• /
• pp.381-390
• /
• 2023

In this study, the mechanical performance of concrete exposed to chloride ion penetration was investigated. And a compressive stress-strain model was presented. CaCl₂ solution was added when mixing concrete to simulate long-term chloride ion penetration, and the concentration of chlorine ions was set to 0, 1, 2, and 4 % based on the weight of the binder. To investigate the compressive stress-strain curve after the peak stress of concrete, the compressive strength was measured by displacement control. When the chlorine ion concentration was 1 %, peak stress increased, but when the chlorine ion concentration was 2 % or more, peak stress decreased. In the case of peak strain, no trend according to chloride ion concentration was observed at 7 days. At 28 days, peak strain decreased as the chloride ion concentration increased. A compressive stress-strain curve model based on the Popovics model was presented using changes in peak stress and peak strain at 28 days. Microstructure analyses were performed to investigate the cause of the decrease in mechanical performance as the concentration of chlorine ions increased. It was confirmed that as the concentration of chlorine ion increased, Friedel's salt increased and portlandite decreased.

• Journal of the Korean Society of Safety
• /
• v.19 no.1
• /
• pp.117-123
• /
• 2004

The prediction to the hydroscopic moisture warping behaviors is analyzed for cellulose-based laminates using a numerical method base on a modified classical laminate(MCL) theory for hygroscopic moisture deformations with cycling testing data. The experimental measurement of the interferometric hygroscopic warping effects, moisture generator, and curvature of cellulose reinforced epoxy laminates is studied under cyclic environmental conditions using a Moire interferometer coupled. Accurate determination of curvatures provides a description of dimensional stability evolution; the tools for validation of computational internal stress and for the warpage prediction in model safety.

• Journal of the Korea Concrete Institute
• /
• v.27 no.5
• /
• pp.521-530
• /
• 2015

Design of fiber reinforced ultra-high strength concrete members should be verified with analytical or experimental methods for safety. Members with compressive strength larger than limitation of current design code usually be designed with analytical verification using stress-strain relation of concrete and reinforcements. For this purpose, mechanical characteristics of steel fiber reinforced ultra-high strength concrete were defined under uniaxial compression. Mix proportions of test specimens were based on reactive powder concrete and straight steel fibers were mixed with different volume fraction. Compressive strength of matrix were distributed from 80 MPa to 200 MPa. Effect of fiber inclusion were investigated : increase of compressive strength of concrete, elastic modulus and strain corresponding to peak stress. For the wide range application of investigation, previously tested test specimens were collected and used for investigation and estimation equation. Based on the investigation and evaluation of previous research results and estimation equation of mechanical characteristics of concrete, regression equations were suggested.

• Journal of the Microelectronics and Packaging Society
• /
• v.26 no.4
• /
• pp.47-53
• /
• 2019

Stiffness-gradient stretchable electronic packages of the soft PDMS/hard PDMS/PTFE structure were processed using the polydimethylsiloxane (PDMS) as the base substrate and the more stiff polytetrafluoroethylene (PTFE) as the island substrate, and their stretchable deformation-resistance characteristics were characterized. The flip-chip joints, formed by bonding the chip bumps of 50 ㎛-diameter onto the PDMS/PTFE substrate pads, exhibited an average contact resistance of 96 mΩ. When the stretchable package of the soft PDMS/hard PDMS/PTFE structure was deformed to 30% elongation, the strain on the PTFE was restrained to 1%, resulting in a negligible resistance increase of 1% in the daisy-chain circuit formed on the PTFE island substrate. The circuit resistance increased for 1.7% after 2,500 cycles of 0~30% stretchable deformation.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.28 no.11C
• /
• pp.1140-1151
• /
• 2003

This paper proposes a face recognition method based on modified Otsu's binarization and Hu moment. Proposed method is robust to brightness, contrast, scale, rotation, and translation changes. As the proposed modified Otsu's binarization computes other thresholds from conventional Otsu's binarization, namely we create two binary images, we can extract higher dimensional feature vector. Here the feature vector has properties of robustness to brightness and contrast changes because the proposed method is based on Otsu's binarization. And our face recognition system is robust to scale, rotation, and translation changes because of using Hu moment. In the perspective of brightness, contrast, scale, rotation, and translation changes, experimental results with Olivetti Research Laboratory (ORL) database and the AR database showed that average recognition rates of conventional well-known principal component analysis (PCA) are 93.2% and 81.4%, respectively. Meanwhile, the proposed method for the same databases has superior performance of the average recognition rates of 93.2% and 81.4%, respectively.

• Journal of the Korean Geotechnical Society
• /
• v.31 no.9
• /
• pp.17-27
• /
• 2015

We perform a series of experimental tests to evaluate whether the shear strength of clean sands can be reliably predicted from shear wave velocity. Isotropic drained triaxial tests on clean sands reconstituted at different relative densities are performed to measure the shear strength and bender elements are used to measure the shear wave velocity. Laboratory tests reveal that a correlation between shear wave velocity, void ratio, and confining pressure can be made. The correlation can be used to determine the void ratio from measured shear wave velocity, from which the shear strength is predicted. We also show that a unique relationship exists between maximum shear modulus and effective axial stress at failure. The accuracy of the equation can be enhanced by including the normalized confining pressure in the equation. Comparisons between measured and predicted effective friction angle demonstrate that the proposed equation can accurately predict the internal friction angle of granular soils, accounting for the effect of the relative density, from shear wave velocity.

• Journal of the Korean Institute of Gas
• /
• v.12 no.4
• /
• pp.34-40
• /
• 2008

Using the finite element method and Taguchi's design technique, the displacement in vertical direction, von Mises stress, and strain energy of the corrugation damper have been analyzed as functions of the extruded length and the thickness of the corrugation damper, and the upper and lower corner radii of the damper. The optimized profile design elements of a corrugation damper are very important for increasing a strain energy absorption capacity of a helmet structure, which is attacked by impulsive external forces. In this study, the optimized design data based on the Taguchi's method was computed as a corrugation damper length of L = 20 mm, a damper thickness of t = 2 mm, the upper corner radius of $R_1=4\;mm$, and the lower corner radius of $R_2=3\;mm$. The optimized design parameters of a corrugation damper indicated that the thickness and extruded length of a corrugation damper may affect to increase the strain energy, which absorbs the impact forces of the helmet.

• Journal of the Korea Concrete Institute
• /
• v.28 no.3
• /
• pp.279-288
• /
• 2016

The present study simplified the moment-curvature relationship to straightforwardly determine the flexural behavior of reinforced concrete (RC) columns. For the idealized column section, moments and neutral axis depths at different stages(first flexural crack, yielding of tensile reinforcing bar, maximum strength, and 80% of the maximum strength at the descending branch) were derived on the basis of the equilibrium condition of forces and compatibility condition. Concrete strains at the extreme compression fiber beyond the maximum strength were determined using the stress-strain relationship of confined concrete, proposed by Kim et al. The lateral load-displacement curves converted from the simplified moment-curvature relationship of columns are well consistent with test results obtained from column specimens under various parameters. The moments and the corresponding neutral axis depth at different stages were formulated as a function of longitudinal reinforcement and transverse reinforcement indices and/or applied axial load index. Overall, curvature ductility of columns was significantly affected by the axial load level as well as concrete compressive strength and the amount of longitudinal and transverse reinforcing bars.

• Journal of Korean Society of Steel Construction
• /
• v.28 no.2
• /
• pp.65-74
• /
• 2016

A finite element dynamic simulation is performed to gain an insight about the stiffened blast wall structures subjected to blast loading. The simulation was verified using qualitative and quantitative comparisons for different materials. Based on in-depth examination of blast simulation recordings, dynamic behaviors occurred in the blast wall against the explosion are determined. Subsequent simulation results present that the blast wall made of the high performance steel performs much better in the shock absorption. In this paper, the existing finite element shock analysis using the LS-DYNA program is further extended to study the dynamic response of the stiffened blast wall made of the high-performance steel considering high strain-rate effects. The numerical results for various parameters were verified by comparing different material models with dynamic effects occurred in the stiffened blast wall from the explosive simulation.