• Journal of the Korean Geosynthetics Society
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• v.19 no.1
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• pp.93-101
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• 2020

In order to predict the nonlinear behaviour of the soil, the elasto-plastic hyperbolic model was selected, which was considered to be relatively simple and highly predictable. The soil parameter determination and the behavior analysis program were developed by formalizing the functions related to the constitutive model. Each soil parameter was determined from the results of the drained triaxial compression tests of Baekma river sand with the change of relative density. The stress-strain behavior was predicted using the soil parameters determined under each condition. As a result, the deviator stress for the axial strain is verified to have a good match between the measured value and predicted value at each relative density. In the relationship between the volumetric stain and the axial strain, when the relative density is loose, the measured value and predicted value tend to match, and when relative density is dense, the predicted value of the volumetric strain appears somewhat smaller than the measured value due to the limitation of the constitutive model.

• Geotechnical Engineering
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• v.12 no.5
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• pp.127-136
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• 1996

Recently, EPS which has unit weight of only 20~30kg/m3, is used for acquiring the safety of settlement and bearing capacity, In Korea, EPS was first used in 1993 as backfill material for abutment that was constructed on soft ground in Inchon. Since then EPS has been used increasingly as backfill material. However, adequate modelling has not yet been proposed for the prediction of the behavior of EPS. Only it's design strength was proposed as the results of unconfined strength and creep test. Accordingly this paper executed triaxial compression test on EPS with various density and confining pressure. Through the analysis of test data the behavior of EPS for strainstress, tangential modulus and poisson's ratio can be expressed in functions with parameters of density and confining pressure of EPS. From these results, this paper proposed a nonliner model describing the behavior of EPS.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.2 s.54
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• pp.95-104
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• 2007

Three types of high-rise RC building structures having irregularity in the lower two stories were selected as prototypes and were performed nonlinear static analysis by using OpenSees to verify the analysis technique and to investigate the seismic capacity of those buildings. The first one has a symmetrical moment resisting frame (Model 1), the second has an infilled shear wall in the central frame (Model 2), and the third has an infilled shear wall only in one of exterior frames (Model 3). Fiber model, which consists of concrete and reinforcing bar represented from stress-strain relationship, is adapted used for simulate the nonlinearity of members, and MVLEM(Multi vertical linear element model) is used for simulate the behavior of wall. The analytical results are simulate the behavior of piloti stories well, for example, the stiffness and yield farce of piloti stories, the up-lift of wall and the variation of lateral stiffness of column due to the variation of axial forces. Overstrength of Model 2 and Model 3 are about 2 times larger than that of Model 1. The reason of the high oversttrength and ductility of Model 2 and Model 3 is that the conservative design of Model 2 and Model 3, whose beam and column sections are the same as those of Model 1. The ductilities of Model 1 and Model 3 are slightly larger than that of Model 1 and Model 3. Model 1 and Model 3 reached mechanism condition, whereas Model 2 failed to the shear failure of shear wall and the large axial forces in columns due to large overturning moment.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.6
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• pp.423-430
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• 2013

In this research, a paramteric study to account for the effect of interfacial strength and nanotube agglomeration on the elastoplastic behavior of carbon nanotube reinforced polypropylene composites is performed. At first, the elastoplastic behavior of nanocomposites is predicted from molecular dynamics(MD) simulations. By combining the MD simulation results with the nonlinear micromechanics model based on the Mori-Tanaka model, a two-step domain decomposition method is applied to inversely identify the elastoplastic behavior of adsorption interphase zone inside nanocomposites. In nonlinear micromechanics model, the secant moduli method combined with field fluctuation method is used to predict the elastoplastic behavior of nanocomposites. To account for the imperfect material interface between nanotube and matrix polymer, displacement discontinuity condition is applied to the micromechanics model. Using the elastoplastic behavior of the adsorption interphase zone obtained from the present study, stress-strain relation of nanocomposites at various interfacial bonding condition and local nanotube agglomeration is predicted from nonlinear micromechanics model with and without the adsorption interphase zone. As a result, it has been found that local nanotube agglomeration is the most important design factor to maximize reinforcing effect of nanotube in elastic and plastic behavior.

• Journal of Korean Society of Steel Construction
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• v.12 no.3 s.46
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• pp.281-290
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• 2000

In this study, we have quantitatively estimated the mechanical properties of structural welding steels widely used in steel structures after correcting the millsheets of the steels using statistical technique. From this result, in present, the mechanical properties of the steels produced in domestics have satisfied the prescribed values in Korean Standards. The mechanical properties of the steels were dependent upon the plate thickness & class of the steels. Also, there have been linear relations between the plate thickness & class of the steels and the mechanical properties of the steels. And the results of this study have shown the similar tendencies with the existing results. Because the upper limit value of yield strength is not prescribed at Korean Standards in present, it is necessary to prescribe the upper limit value of yielding ratio(or yield strength) in order to assure the deformation performance of the steels.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4A
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• pp.611-622
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• 2008

Nonlinear analyses have been carried out for both bridge piers and a bridge structure being repaired using a repair element in order to assess the post-repair seismic response of such structures. For this purpose, a simplified CFRP stress-strain model has been proposed. The analytical predictions incorporating the current developments correlate reasonably well with experimental results in terms of strength and stiffness. In addition, nonlinear dynamaic analyses have also been conducted for a bridge structure in terms of the created multiple earthquake sets to evaluate the effect of pier repair on the response of a whole bridge structure. In these analyses, potential plastic hinge zones of piers are virtually repaired by CFRP and steel jacketing. Comparative results prove the virtual necessity of performing nonlinear post-repair analyses under multiple earthquakes, particularly when the post-repair response features are required. In all, the present approaches are expected to provide salient information regarding a healthy seismic repair intervention of a damaged strcuture.

• Journal of the Korean GEO-environmental Society
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• v.18 no.2
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• pp.29-37
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• 2017

As the behavior of the debris flow due to the torrential rains in mountain is affected by shear strength and rheological properties of the fine fraction in the ground, the evaluation of both properties is necessary to estimate the behavior of the debris flow. The objective of this study is to evaluate the shear strength and rheological properties using the direct shear apparatus. The direct shear tests are conducted for two kinds of fine-grained soil specimens, which are in dry state and liquid limit state. From the direct shear tests, shear strengths are measured according to the normal stresses applied on the specimens to evaluate the cohesion and internal friction angle. In addition, reversal shear tests are performed for the fine-grained soil specimens in liquid limit state according to the shear rate to evaluate the residual shear strength. The results of direct shear tests show that the specimen at the liquid limit state has lower internal friction angle and higher cohesion compared to the dry stated, and the residual friction angle and cohesion at the residual state are lower than those at the peak state. In the result of reversal shear test, the residual shear strength is directly proportional to the shear rate and viscosity is calculated as $73.60Pa{\cdot}s$. This study demonstrates that the direct shear apparatus can be effectively used for the evaluation of the shear strength and rheological properties of the fine-grained soils related with the debris flow.

• Journal of the Korean Geotechnical Society
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• v.36 no.12
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• pp.77-86
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• 2020

In this study, the importance of implied strength correction for shallow depths at a region of moderate to low seismicity with primary focus on its effect upon site natural period and mean period of the ground motion is investigated. In addition to the most commonly used Modified Kondner-Zelasko (MKZ) model, this paper uses a quadratic/hyperbolic (GQ/H) model that can capture the stress - strain response at large strains as well as small strain stiffness dependence. A total of six site profiles by downhole tests are used and 1D site response analyses are performed using three input motions with contrasting mean periods. The difference between non-corrected and corrected analyses is conditional on the site period as well as mean ground motion period. The effect of periods is analyzed by correlating them with the effective peak ground acceleration, maximum shear strains and amplification factors. The comparative study reveals that the difference is more prominent in soft sites with long site periods. Insignificant differences are observed when soil profiles are subjected to ground motion with very short mean period.

• Journal of the Korean Geotechnical Society
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• v.27 no.10
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• pp.81-92
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• 2011

The rheological properties of Wyoming bentonites are strongly influenced by the size of particles, cation exchangeable capacity, arrangement and morphology of clay mineral. This paper presents the results of rheological investigations on the Wyoming bentonites aqueous dispersions: two types of particle flocculation were considered. For the Wyoming bentonite, 0g/L and 30g/L NaCl equivalent salinity were added in fresh and salt water to examine the rheological behavior. This paper examined the general rheological characteristics, compatibility of rheological models and correlation between soil structure and change in rheological properties of Wyoming bentonite caused by increasing salinity. From flow curves of bentonites hydrated with fresh water and salt water, the observed general flow behavior is very close to shear thinning with yield stress (or ideal Bingham fluid with yield stress and plastic viscosity). However, the change of shear stress at the same shear rate is clear, particularly for lower shear rate. Well-known rheological models are used to fit the data. There is a good agreement between rheological model and data: Carreau, Herschel-Bulkley and power-law for S=0g/L and bilinear, Herschel-Bulkley and power-law for S=30g/L. It may be due to the fact that the internal structural bonding (strong modification of particle-particle interactions from edge-to-edge and/or edge-to-face to face-to-face) in soil matrix is affected from the evolution of rheological properties with different salinities.

• Journal of the Korean GEO-environmental Society
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• v.8 no.6
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• pp.53-60
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• 2007

L/EPS, manufactured in the shape of block and used for civil engineering, is a lightweight material with an excellent resistance to compression, and provides a superb self-sufficient stability. EPS is a suitable material capable of resolving the problem of settlement and lateral flow if it is applied as the soil on soft ground. The Korean Standards (KS) has not yet proposed any testing method for use of EPS as an engineering banking material. Only its testing and quality ordinance as a heat insulation material has been standardized. The design criteria for EPS has been established and applied through the trial construction of KHC (Korea Highway Corporation) and quality test of manufacturer, but most studies on them have been confined to factory products. This study is focused on comparing and analyzing long-term durability by conducting cyclic load test, freezing and thawing test, absorption rate test and others. EPS used in the test was chosen from construction sites and factory products, focusing on the long-term durability of EPS depending on the passage of time. Unconfined compression test results indicated that the strength of collected samples was lower than factory products. While the triaxial compression test results indicated that the shear strength increased in proportion to the increase of confining pressure, and factory products had declining shear strength as the confining pressure rose.