• Journal of the Korean Society for Railway
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• v.10 no.3 s.40
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• pp.264-270
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• 2007

Two modulus, strain modulus $(E_v)$ and subgrade reaction modulus $(K_{30})$ are being used as a standard for bearing stiffness in Korea Railroad design. The first is used in Europe and the other is used in Japan. The methodologies to obtain the two modulus are similar in using plate. But testing methods are different in loading to plate. Therefore, according to soil strain range, there should be large gap in not only computations of deformation modulus but also the necessary time to test. At first, this paper focuses on the two kinds of test methods to evaluate bearing stiffness. Secondly, based on elastic theory, the theory to obtain the two coefficients are studied thoroughly. Finally, the correlations between the two coefficients were analyzed and evaluated based on the field test results more than 38 places. The matching values for subgrade and ground between $K_{30}$ and $E_{v2}$ are proposed with the consideration of the proposed strain reduction factor (1.5 for subgrade and 3 for ground) and safety factor, respectively.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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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.

• Journal of the Korean Society of Safety
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• v.17 no.2
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• pp.52-57
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• 2002

In this study. stress-strain relationships were investigated by performing the confined extension tests for seven types of geosynthetics such as geotextiles, composite geosynthetics and geogrids. A comparison was made between unconfined and confined moduli for each geosynthetic material to quantify the soil confinement effect on stress-strain properties. A comparison was also made between the increase of moduli at the same strain level with the types of the geosynthetics to demonstrate the different stress-strain responses. Based on the result of the extension tests, the higher the confining stress, the larger the secant modulus of geosynthetics. The secant modulus at 5% strain is twice as much as that of 10% strain, especially there is a noticeable increasing of secant modulus for the two nonwoven geotextiles.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.4
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• pp.148-153
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• 2004

It is well-known that the mechanical behavior of fiber-reinforced composites under hydrostatic pressure environment is different from that of atmospheric pressure environment. It is also known that the mechanical behavior of fiber-reinforced composites is affected by a strain rate. In this work, we investigated the effect of strain rate on the compressive elastic modulus, fracture stress, and fracture strain of carbon/epoxy composites under hydrostatic pressure environment. The material used in the compressive test was unidirectional carbon/epoxy composites and the hydrostatic pressures applied was 270㎫. Compressive tests were performed applying three strain rates of 0.05％/sec, 0.25％/sec, and 0.55％/sec. The results showed that the elastic modulus increased with increasing strain rate while the fracture stress was little affected by the strain rate. The results also showed that the fracture strain decreased with increasing strain rate.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.345-352
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• 2000

It is very important to evaluate the reliable nonlinear modulus characteristics of soils not only in the analysis of geotechnical structures under working stress conditions but also for the soil dynamic problems. For the evaluation of modulus characteristics of soils, various tests have been mostly employed in laboratory. However, different testing techniques are likely to have different ranges of reliable strain measurements, different applied stress level, and different loading frequencies, and the modulus of soils can be affected by these variables. For reliable evaluation, therefore, those effects on the modulus need to be considered, and measured values should be effectively adjusted to actual conditions where the soil is working. In this paper, to evaluate the modulus characteristics of soils, laboratory testing such as free-free resonant column (FF-RC), resonant column (RC), torsional shear (TS), static TX, and cyclic M/sub R/ tests were performed. The effects of strain amplitude, loading frequency, loading cycles, confining pressure, density, and water content on modulus were investigated. It is shown that the FF-RC test, which is simple and inexpensive testing technique, can provide a reliable estimation of small strain Young's modulus (E/sub max/), and the modulus evaluated by various laboratory tests are comparable to each other fairly well when the effects of these factors are properly taken into account.

• Journal of the Korean Society for Railway
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• v.11 no.1
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• pp.61-68
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• 2008

Resilient modulus has been used for characterizing the stress-strain behavior of subgrade soils subjected to traffic loadings. With the recent release of the M-E Design Guide, highway agencies are further encouraged to implement the resilient modulus test to improve subgrade design. The subgrade design for the trackbed, however, is primarily relying on the static test results such as $K_{30}$ and deformation modulus, Ev. Therefore applicability of the resilient modulus for the design of trackbed needs to be evaluated. In this study, physical property tests, unconfined compressive tests and resilient modulus tests were conducted to assess the resilient and permanent strain behavior of 14 cohesive subgrade soils. A predictive model for estimating the resilient modulus is proposed based on the results of unconfined compressive tests and tangent elastic modulus, unconfined compressive strength, failure strain, secant modulus at peak, and yield strain. The predicted resilient moduli using the predictive models compared satisfactorily with measured ones. Although the permanent strain occurs during the resilient modulus test, the permanent behavior of subgrade soils is currently not taken into consideration.

• Journal of the Korean Geotechnical Society
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• v.24 no.6
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• pp.57-67
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• 2008

Two test methods, nonrepetitive plate loading test (NPLT) and repetitive plate loading test (RPLT) are being used to control the quality of compaction through the evaluation of the stiffness of subgrade soils in the Korea railway industry. Subgrade reaction modulus ($k_{30}$) from the NPLT and strain modulus ($E_v$) from the RPLT are the index values to check them. The methods have similar aspects, but they differ in the modulus evaluation method, the numbers of loading stage, termination procedures, etc. This paper analyses the differences of the two test methods and evaluates the relationship between subgrade reaction modulus and strain modulus. In order to develop the relationship, total 22 tests were performed including the NPLT and the RPLT at the 6 original grounds, and 5 upper or lower subgrades in Kyungbu High Speed Railway II stage construction sites. According to the soil conditions, the relationship between subgrade reaction modulus and strain modulus was proposed with corrections by considering strain states, mean confining pressures, and Poisson's ratio.

• Transactions of Materials Processing
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• v.13 no.5
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• pp.409-414
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• 2004

TRIP steel has got attention in automobile industry because of its high strength and high formability. However, the information on deformation behavior of TRIP steel, including bending and springback, is not enough until now. In this research, the V-die bending experiment and analysis have been done to obtain the information of springback of TRIP steel. And a new numerical method, where elastic modulus is varied with the change of the strain, was suggested. Tensile test for TRIP steel was done to get tensile properties as well as strain dependency of elastic modulus of the material. Strain-dependency of elastic modulus was used the numerical analysis of V-die bending and unbending process to predict springback amount. The results were compared with experiment, showing reasonable agreement. Through the analysis of V-die bending as well as draw bending of TRIP steel, the proposed scheme with variable elastic modulus was proven to well predict the deformation behavior of TRIP steel during bending and springback.

• Geotechnical Engineering
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• v.13 no.4
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• pp.109-120
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• 1997

In the working stress conditions, the strain level in a soil mass experienced by existing structures and during construction is less than about 0.1-1%. In order to analyse the deformational behavior accurately, the in-situ testing technique which provides the reliable deformational characteristics at small strains, needs to be developed. The purpose of this paper is to measure the small-strain shear modulus of soils by using pressuremeter test(PMT). PMT is a unique method for assessing directly the in-situ shear modulus of soils with strain amplitude. For the accurate small strain measurements without initial disturbance effect, the unloading-reloading cycle was used and the measured modulus was corrected in view of the relevant stress and strain levels around the PMT probe during testing. Not only in the calibration chamber but in the field, PMT tests were performed on the cohesionless soils. The variation in shear modulus with strain amplitude ranging from 10-2% to 0.5% was reliably determined by PMT PMT results were also compared with other in-situ and laboratory test results. Moduli obtained from different testing techniques matched very well if the effect of strain amplitude was considered in the com pall son.

• Journal of the Korean Geotechnical Society
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• v.18 no.3
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• pp.126-126
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• 2002

In dynamic analyses such as seismic ground response and soil-structure interaction problems, it is very crucial to obtain accurate dynamic shear modulus of soil deposit. In this study, an extensive data base of available experimental data is compiled and reanalyzed to establish a simple empirical formula for the dynamic shear modulus reduction curve to cover wide range of strain for sandy soils. The proposed empirical equation is to represent the dynamic shear modulus degradation with strain in terms of low-amplitude dynamic shear modulus and effective mean confining Pressure, since those factors have the most significant effect on the Position and shape of the shear modulus reduction curve for nonelastic soils. If low-amplitude shear modulus is measured, degraded modulus at any shear strain amplitude can be calculated using the proposed equation.