• Geomechanics and Engineering
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• 제28권1호
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• pp.89-105
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• 2022

The behavior of the soil subgrade is complex and irregular against loads. When modeling, the soil is often replaced by a more straightforward system called a subgrade model. The Winkler method of linear elastic springs is a popular method of soil modeling in which the spring constant shows the modulus of subgrade reaction. In this research, the factors affecting the distribution of the modulus of subgrade reaction of elastoplastic subgrades are examined. For this purpose, critical theories about the modulus of subgrade reaction were examined. A square raft foundation on a sandy soil subgrade with was analyzed at different internal friction angles and Young's modulus values using ABAQUS software. To accurately model the actual soil behavior, the elastic, perfectly plastic constitutive model was applied to investigate a foundation on discrete springs. In order to increase the accuracy of soil modeling, equations have been proposed for the distribution of the subgrade reaction modulus. The constitutive model of the springs is elastic, perfectly plastic. It was observed that the modulus of subgrade reaction under an elastic load decreased when moving from the corner to the center of the foundation. For the ultimate load, the modulus of subgrade reaction increased as it moved from the corner to the center of the foundation.

• 소음진동
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• 제2권2호
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• pp.99-106
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• 1992

The complex Young's modulus of a viscoelastic material can be obtained as a function of frequency from the measurements of relative motion between the two ends of a bar-type specimen. Non-resonance method is usually used to obtain the complex Young's modulus over wide range of frequency including resonance points, while in resonance method information at resonance frequencies only is used. However, the complex Young's modulus obtained by the non-resonance method is often unreliable in the anti-resonance frequency regions because of the measurement noise problems. In this study, the effects of the random measurement errors on estimating the complex Young's modulus are studied in the aspect of sensitivity, and how to obtain the reliable frequency region for a given measurement error level is shown. The usable frequency regions in determining the complex Young's modulus are represented by a non-dimensional parameter formed with the wave length and specimen length.

• 비파괴검사학회지
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• 제36권1호
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• pp.9-17
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• 2016

The elastic modulus of a 3D-printed Kelvin foam plate is investigated by measuring the acoustic wave velocity of 1 MHz ultrasound. An isotropic tetrakaidecahedron foam with 3 mm unit cell is designed and printed layer upon layer to fabricate a Kelvin foam plate of 14 mm thickness with a 3D CAD/printer using ABS plastic. The Kelvin foam plate is completely filled with paraffin wax for impedance matching, so that the acoustic wave may propagate through the porous foam plate. The acoustic wave velocity of the foam plate is measured using the time-of-flight (TOF) method and is used to calculate the elastic modulus of the Kelvin foam plate based on acousto-elasticity. Finite element method (FEM) and micromechanics is applied to the Kelvin foam plate to calculate the theoretical elastic modulus using a non-isotropic tetrakaidecahedron model. The predicted elastic modulus of the Kelvin foam plate from FEM and micromechanics model is similar, which is only 3-4% of the bulk material. The experimental value of the elastic modulus from the ultrasonic method is approximately twice as that of the numerical and theoretical methods because of the flexural deformation of the cell edges neglected in the ultrasonic method.

• 한국도로학회논문집
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• 제15권3호
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• pp.65-74
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• 2013

PURPOSES: This study is to evaluate the dynamic modulus changes of permeable asphalt mixtures by using non-destructive impact testing method and to compare the dynamic moduli of permeable asphalt mixtures through repeated freezing and thawing conditions. METHODS: For the study, non-destructive impact testing method is used in order to obtain dynamic modulus of asphalt specimen and to confirm the change of dynamic modulus before and after freezing and thawing conditions. RESULTS : This study has shown that the dynamic moduli of asphalt concrete specimens consisting of 10%, 15% and 20% porosity are reduced by 11.851%, 1.9564%, 24.593% after freezing and thawing cycles. CONCLUSIONS : Non-destructive impact testing method is very useful and has repeatability. Specimen with 15% porosity has high durability than others.

• Computers and Concrete
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• 제20권1호
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• pp.49-56
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• 2017

A clear correlation exists between the compressive strength and elastic modulus of concrete. Unfortunately, determining the static elastic modulus requires destructive methods and determining the dynamic elastic modulus is greatly complicated by the shape and size of the specimens. This paper reports on a novel approach to the prediction of compressive strength in concrete cylinders using numerical calculations in conjunction with the impact-echo method. This non-destructive technique involves obtaining the speeds of P-waves and S-waves using correction factors through numerical calculation based on frequencies measured using the impact-echo method. This approach makes it possible to calculate the dynamic elastic modulus with relative ease, thereby enabling the prediction of compressive strength. Experiment results demonstrate the speed, convenience, and efficacy of the proposed method.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.320-325
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• 2009

The constrained modulus, representative property to evaluate compressibility of soil, is needed to estimate the settlement of ground structure. A series of lab and field cone penetration tests for clayey soil of Busan new-port and Noksan industrial area were conducted to evaluate the estimation method of constrained modulus. Since CPT generates large deformation of ground, it is difficult to correlate the cone resistance with the constrained modulus. Therefore, appropriate correlation between them is essential to estimate the constrained modulus based on CPT results. The test results show that the ratio of the constrained modulus to the cone resistance is inversely proportional with plasticity index. Based on this result, the estimation method of constrained modulus for Busan clay is suggested.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.933-943
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• 2009

Axial loads and shaft resistances can be calculated by load transfer analysis using strain data with load level. In load transfer analysis, the elastic modulus of concrete is a one of the most important parameters to consider. The elastic modulus, $E_{50}$, suggested by ACI (American Concrete Institute), has been commonly used. However, elastic modulus of concrete shows nonlinear stress-strain characteristic, so nonlinearity should be considered in load transfer analysis. In this paper, a load transfer analysis was performed by using data obtained from bi-directional pile load tests for four cases of drilled shafts. For consideration of nonlinearity, elastic modulus was calculated by both the Fellenius method and the nonlinear method, assuming the stress-strain relation of concrete to be a quadratic function, and then, the calculated elastic modulus was applied to the estimation of shaft resistance. The calculated shaft resistances were compared with the result obtained using the constant elastic modulus of ACI code. It was found that the f-w curves are similar to each method, and elastic modulus and shaft resistances decreased as strain increased. Moreover, shaft resistances estimated from elastic modulus considering nonlinearity were 5~15% different than those obtained using the constant elastic modulus.

• 한국도로학회논문집
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• 제16권3호
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• pp.43-50
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• 2014

PURPOSES : The dynamic modulus can be determined by applying the various theories from the Impact Resonance Testing(IRT) Method. The objective of this paper is to determine the best theory to produce the dynamic modulus that has the lowest error as the dynamic modulus data obtained from these theories(Complex Wave equation Resonance Method related to either the transmissibility loss or not, Dynamic Stiffness Resonance Method) compared to the results for dynamic modulus determined by using the Universal Testing Machine. The ultimate object is to develop the predictive model for the dynamic modulus of a Linear Visco-Elastic specimen by using the Complex Wave equation Resonance Method(CWRM) came up for an existing study(S. O. Oyadiji; 1985) and the Optimization. METHODS : At the destructive test which uses the Universal Testing Machine, the dynamic modulus results along with the frequency can be used for determining the sigmoidal master curve function related to the reduced frequency by applying Time-Temperature Superposition Principle. RESULTS : The constant to be solved from Eq. (11) is a value of 14.13. The reduced dynamic modulus obtained from the IRT considering the loss factor related to the impact transmissibility has RMSE of 367.7MPa, MPE of 3.7%. When the predictive dynamic modulus model was applied to determine the master curve, the predictive model has RMSE of 583.5MPa, MPE of 3.5% compared to the destructive test results for the dynamic modulus. CONCLUSIONS : Because we considered that the results obtained from the destructive test had the most highest source credibility in this study, the dynamic modulus data obtained respectively from DSRM, CWRM were compared to the results obtained from the destructive test by using th IRT. At the result, the reduced dynamic modulus derived from DSRM has the most lowest error.

• 한국도로학회논문집
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• 제14권5호
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• pp.57-65
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• 2012

PURPOSES: It is important to consider the long-term performance of concrete pavement, because concrete pavement is more exposed to the various environmental conditions than any other concrete structures. One of the several methods to evaluate the long-term performance of concrete during winter is KS F 2456. Relative dynamic modulus of elasticity shows the resistance to freezing and thawing. METHODS: To measure relative dynamic modulus of elasticity, ultra sonic is generally used. But in this study, to measure the relative dynamic modulus of elasticity, both ultra sonic and shear wave were used and then compared each other. RESULTS: The results from the measurement by ultrasonic wave and shear wave were divided into three types. Type 1 : Specimens are good and relative dynamic modulus of elasticity did not decrease until 300 cycle. Type 2 : The relative dynamic modulus of elasticity decreased from the late cycle.(about 150 cycle later) Type 3 : The relative dynamic modulus of elasticity consistently decreased from the beginning. As a result of ANOVA, there is no difference according to measuring method, in type 2 and 3. But there is a difference according to measuring method, in type 1's relative dynamic modulus of elasticity. CONCLUSIONS: It is proved that shear wave can be used to understand the damage tendency of relative freezing and thawing and to measure the relative dynamic modulus of elasticity.

• Journal of the Korean Wood Science and Technology
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• 제39권5호
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• pp.398-405
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• 2011

Nondestructive evaluation (NDE) technique method using a resonance frequency mode was carried out for woodceramics made by different phenol resin impregnation ratios (40, 50, 60, 70%) for Broussonetia Kazinoki Sieb. Dynamic modulus of elasticity increased with increasing resin impregnation ratios. There was a close relationship between dynamic modulus of elasticity and static bending modulus of elasticity and between dynamic modulus of elasticity and MOR and between static bending modulus of elasticity and MOR. Therefore, the dynamic modulus of elasticity using resonance frequency mode is useful as a nondestructive evaluation method for predicting the MOR of woodceramics made by different impregnation ratios.