• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.6
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• pp.306-318
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• 2018

In order to evaluate the seismic capacity of massive vertical type breakwaters which have intensively been deployed along the coast of South Korea over the last two decades, we carry out the preliminary numerical simulation against the PoHang, GyeongJu, Hachinohe 1, Hachinohe 2, Ofunato, and artificial seismic waves based on the measured time series of ground acceleration. Numerical result shows that significant sliding can be resulted in once non-negligible portion of seismic energy is shifted toward the longer period during its propagation process toward the ground surface in a form of shear wave. It is well known that during these propagation process, shear waves due to the seismic activity would be amplified, and non-negligible portion of seismic energy be shifted toward the longer period. Among these, the shift of seismic energy toward the longer period is induced by the viscosity and internal friction intrinsic in the soil. On the other hand, the amplification of shear waves can be attributed to the fact that the shear modulus is getting smaller toward the ground surface following the descending effective stress toward the ground surface. And the weakened intensity of soil as the number of attacking shear waves are accumulated can also contribute these phenomenon (Das, 1993). In this rationale, we constitute the numerical model using the model by Hardin and Drnevich (1972) for the weakened shear modulus as shear waves go on, and shear wave equation, in the numerical integration of which $Newmark-{\beta}$ method and Modified Newton-Raphson method are evoked to take nonlinear stress-strain relationship into account. It is shown that the numerical model proposed in this study could duplicate the well known features of seismic shear waves such as that a great deal of probability mass is shifted toward the larger amplitude and longer period when shear waves propagate toward the ground surface.

• Journal of the Korean Geotechnical Society
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• v.21 no.3
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• pp.27-42
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• 2005

In this study, dynamic deformation characteristics of sands under dry, saturated drained and undrained conditions were investigated at small to intermediate strains using the modified Stokoe-type torsional shear tests. The equipment was modified to saturate the specimen and to maintain the B-value above 0.99 during the test. On two types of sands, Geumgang sand from Korea and Toyoura sand from Japan, tests were carried out at various drainage conditions, void ratios, and effective confining pressures. Based on the test results, dynamic deformation characteristics, shear modulus (G) and damping ratio (D), and/or pore-water pressure were measured with strain amplitude and number of loading cycles. Variations of G and D at small ($\gamma_c<{10}^{-3}\%$) to medium (${10}^{-3}\%<\gamma_c<{10}^{-1}\%$) strains were measured under various drainage conditions, and test results were intensively compared considering drainage conditions.

• International Journal of Reliability and Applications
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• v.5 no.1
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• pp.1-13
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• 2004

It is recently well recognized that the technique for the one-sided stress wave velocity measurement in structural materials provides measurement in structural materials provides valuable information on the state of the material such as quality, uniformity, location of cracked or damaged area. This technique is especially effective to measure velocities of longitudinal and Rayleigh waves when access to only one surface of structure is possible. However, one of problems for one-sided stress wave velocity measurement is to get consistent and reliable source for the generation of elastic wave. In this study, the laser based surface elastic wave was used to provide consistent and reliable source for the generation of elastic wave into the materials. The velocities of creeping wave and Rayleigh wave in materials were measured by the one-sided technique using laser based surface elastic wave. These wave velocities were compared with bulk wave velocities such as longitudinal wave and shear wave velocities to certify accuracy of measurement. In addition, the mechanical properties such as poisson's ratio and specific modulus(E/p) were calculated with the velocities of surface elastic waves.

• Nuclear Engineering and Technology
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• v.53 no.6
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• pp.2000-2010
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• 2021

Mechanical moduli, such as Young's modulus (E), Bulks modulus (B), Shear modulus (S), longitudinal modulus (L), Poisson's ratio (σ) and micro Hardness (H) were theoretically calculated for (100-x)TeO₂+x MgO glasses, where x = 10, 20, 30, 40 and 45 mol%, based on the Makishima-Mackenzie model. The estimated results showed that the mechanical moduli and the microhardness of the glasses were improved with the increase of the MgO contents in the TM glasses, while Poisson's ratio decreased with the increase in MgO content. Moreover, the radiation shielding capacity was evaluated for the studied TM glasses. Thus, the linear attenuation coefficient (LAC), mass attenuation coefficient (MAC), transmission factor (TF) and half-value thickness (𝚫_0.5) were simulated for gamma photon energies between 0.344 and 1.406 MeV. The simulated results showed that glass TM10 with 10 mol % MgO possess the highest LAC and varied in the range between 0.259 and 0.711 cm^-1, while TM45 glass with 45 mol % MgO possess the lowest LAC and vary in the range between 0.223 and 0.587 cm^-1 at gamma photon energies between 0.344 and 1.406 MeV. Furthermore, the BXCOM program was applied to calculate the effective atomic number (Z_eff), equivalent atomic number (Z_eq) and buildup factors (EBF and EABF) of the glasses. The effective removal cross-section for the fast neutrons (ERCSFN, ∑_R) was also calculated theoretically. The received data depicts that the lowest ∑_R was achieved for TM10 glasses, where ∑_R = 0.0193 cm² g^-1, while TM45 possesses the highest ERCSFN where ∑_R = 0.0215 cm² g^-1.

• Geomechanics and Engineering
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• v.15 no.4
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• pp.987-995
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• 2018

In this study, a relationship between small-strain shear modulus ($G_{max}$) and overconsolidation ratio (OCR) based on shear wave velocity ($V_S$) measurement was established to identify the stress history of centrifuge model ground. A centrifuge test was conducted in various centrifugal acceleration levels including loading and unloading sequences to cause various stress histories on centrifuge model ground. The $V_S$ and vertical effective stress were measured at each level of acceleration. Then, a sensitivity analysis was conducted using testing data to ensure the suitability of OCR function for the tested cohesionless soils and found that OCR can be estimated based on $V_S$ measurements irrespective of normally-consolidated or overconsolidated loading conditions. Finally, the developed $G_{max}$-OCR relationship was applied to centrifuge models constructed and tested under various induced stress-history conditions. Through a series of tests, it was concluded that the induced stress history on centrifuge model by compaction, g-level variation, and past overburden load can be analysed quantitatively, and it is convinced that the OCR evaluation technique will contribute to better interpret the centrifuge test results.

• Geomechanics and Engineering
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• v.8 no.1
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• pp.1-15
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• 2015

This paper presents a series of conventional undrained triaxial compression tests conducted to determine the effect of both tire crumbs and cement addition on Narli sand specimens. The tire crumb contents and cement contents were 3%, 7%, 15%; and 1%, 3%, 5% by dry weight of the sand specimens respectively. Specimens were prepared at about 35% relative density, cured during overnight (about 17 hours) for artificially bonding under a 100 kPa effective stress (confining pressure of 500 kPa with a back pressure of 400 kPa), and then sheared. Deviatoric stress-axial strain, pore water pressure-axial strain behavior, and Young's modulus of the specimens at various mixture ratios of tire crumb/cement/sand were measured. Test results indicated that the addition of tire crumb to sand decreases Young's modulus, deviatoric stress and brittleness, and increase pore water pressure generation. The addition of cement to sand with tire crumbs increases deviatoric stress, Young's modulus, and changes its ductile behavior to a more brittle one. The results suggest that specimen formation in the way used here could reduce the tire disposal problem in not only economically, and environmentally, but also more effectively beneficial way for some geotechnical applications.

• Magazine of the Korean Society of Agricultural Engineers
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• v.32 no.3
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• pp.79-86
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• 1990

Based on limited number of tests on reinforced wood beams using polymer mortar in this study, following conclusions were drawn ; 1.Reinforcing compression side of wood beam using polymer mortar was effective in reducing deflection. 2.By increasing thickness of polymer mortar, effective beam stiffness was improved, but energy absorption was reduced. 3.Polymer mortar reinforcement improved compressive strength and reduced strain in compression side of the beam. Therefore, it was possible to change the failure mode from by compression in control beam to by tension in composite beams. 4.The composite beams that have more than 2cm of polymer mortar layer did not perform well because a strain redistribution and separation of meterials at interface were induced in moment span. 5.To maximize the load carrying capacity of composite beam, it is necessary to make polymer mortar and wood behave together without failing at interface. To do this, it is needed to use a polymer mortar which has high strength with such elastic modulus that is closer to elastic modulus of wood. otherwise, it is recommended to use shear connectors at interface to prevent separation of materials under ultimate load.

• Composites Research
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• v.17 no.1
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• pp.29-37
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• 2004

Honeycomb sandwich composite(HSC) structures have been widely used in aircraft and military industry owing to their light weight and high stiffness. Mechanical properties of honeycomb core materials are needed for accurate analysis of the sandwich composites. In this study. theoretical formula for effective elastic modulus and Poisson's ratio of honeycomb core materials was established using an energy method considering the bending, axial and shear deformations of honeycomb core walls. Finite-element analysis results obtained by using commercial FEA code, ABAQUS 6.3 were comparable to the theoretical ones. In addition, we performed tensile test of HSC plates and analyzed deformation behaviors and interlaminar stresses through its FEA simulation. An increased shear stress along the interface between surface and honeycomb core layers was shown to be the main reason for interfacial delamination in HSC plate under tensile loading.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.4
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• pp.343-348
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• 2009

In this study, an efficient sequential bridging method to characterize both the particle size effect and concentration effect on the mechanical properties of nanocomposites at high volume fraction is suggested through a molecular dynamics(MD) simulations and micromechanics of composites materials. The Young's modulus and the shear modulus of the nanocomposites at various particle radius and at 12% volume fraction were obtained from MD simulations and multi-inclusion model was adopted to describe both modulus in continuum model. In order to describe the particle size effect, an additional phase, effective interface, was adopted as characteristic phase and the non-dilute concentration effect which appears at 12% volume fraction was describe via the variation of the elastic modulus of the infinite medium. Both the elastic modulus of the interface and infinite medium were fitted into functions of particle radius for the applicability of the present bridging method at various particle radii. Using the present bridging method the elastic modulus of the nanocomposites was efficiently obtained with accuracy. In addition, the effect of the interface thickness and modulus on the elastic modulus of the nanocomposite was investigated.

• Journal of the Korean Geotechnical Society
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• v.22 no.11
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• pp.47-54
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• 2006

Shear wave velocity of uncemented soil can be expressed as the function of effective stresses when capillary phenomena are negligible. However, the terms of effective stresses are divided into the direction of wave propagation and polarization because stress states are generally anisotropy. The shear wave velocities are affected by ${\alpha}$ parameters and ${\beta}$ exponents that are experimentally determined. The ${\beta}$ exponents are controlled by contact effects of particulate materials (sizes, shapes, and structures of particles) and the ${\alpha}$ parameters are changed by contact behaviors among particles, material properties of particles, and type of packing (i.e., void ratio and coordination number). In this study, consolidation tests are performed by using clay, mica and sand specimens. Shear wave velocities are measured during consolidation tests to investigate the stress-induced and inherent anisotropies by using bender elements. Results show the shear wave velocity depends on the stress-induced anisotropy for round particles. Furthermore, the shear wave velocity is dependent on particle alignment under the constant evvective stress. This study suggests that the shear wave velocity and the shear modulus should be carefully estimated and used for the design and construction of geotechnical structures.