• Journal of the Korean Geotechnical Society
• /
• v.21 no.9
• /
• pp.53-64
• /
• 2005

For geotechnical design in practice, soils are, in general, assumed to behave as a linear elastic or perfect plastic material. More realistic geotechnical design, however, should take into account various factors that affect soil behavior in the field, such as non-linearity of stress-strain response, stress history, and water content. In this study, a series of laboratory tests including triaxial and resonant column tests were peformed with sands of various silt contents, relative densities, stress states, OCR and water contents. This aims at investigating effects of various factors that affect strength and stiffness of sands. From the results in this study, it is found that the effect of OCR is significant for the intermediate stress-strain range from the initial to failure, while it may be ignored for the initial stiffness and peak strength. For the effect of water content, it is observed that the initial elastic modulus decreases with increasing water content at lower confining stress and relative density At higher confining stresses, the effect of water content Is found to become small.

• Elastomers and Composites
• /
• v.37 no.3
• /
• pp.183-191
• /
• 2002

Rubber materials with excellent damping property are widely applied for vibration isolators. The dynamic characteristics of the rubber materials for vibration isolators were investigated. Dynamic tests for rubber materials with five different hardness were performed. In dynamic tests for test specimen, non-resonance method was used to obtain the dynamic storage modulus and loss factor. Moreover, the effect of dynamic vibration frequency, strain amplitude and temperature were investigated. As results, the storage modulus and loss factor generally increase when the hardness and frequency increase, and the glass transition temperature is $-50^{\circ}C$ by a large change in modulus and loss factor.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.3A
• /
• pp.181-187
• /
• 2011

This paper deals with free vibrations of the Timoshenko beam supported by two elastomeric bearings at two far ends. The ordinary differential equation governing free vibrations of such beam is derived, in which both effects of rotatory inertia and shear deformation are included as the Timoshenko beam theory. Also, boundary conditions of the free end are derived based on the Timoshenko beam theory. The ordinary differential equation is solved by the numerical methods for calculating natural frequencies and mode shapes. Both effects of the rotatory inertia and shear deformation on natural frequencies are extensively discussed. Also, relationships between natural frequencies and slenderness ratio, foundation modulus and bearing length are presented. Typical mode shapes of bending moment and shear force as well as deflection are given in figures which show the positions of maximum amplitudes and nodal points.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.11 no.1 s.53
• /
• pp.67-77
• /
• 2007

Site coefficients in IBC and KBC codes have some limits to predict the rational seismic responses of a structure, because they take into account only the effect of the soil amplification without the effects of the structure-soil interaction. In this study, upper and lower limits of the site coefficients are estimated through the pseudo 3-D elastic seismic response analyses of structures built on the linear or nonlinear soil layers taking Into account the effects of the structure-soil interaction. Soil characteristics of site classes of A, B and C were assumed to be linear, and those of site classes of D and E were done to be nonlinear and the Ramberg-Osgood model was used to evaluate shear modulus and damping ratio of a soil layer depending on the shear wave velocity of the soil layer, Seismic analyses were performed with 12 weak or moderate earthquake records scaled the peak acceleration to 0.1g or 0.2g and deconvoluted as earthquake records at the bedrock located at 30m deep under the outcrop. With the study results of the elastic seismic response analyses of structures, new standard response spectrum and upper and lower limits of the site coefficients of $F_{a}\;and\;F_{v}$ at the short period range and the period of 1 second are suggested including the effects of the structure-soil interaction, and new site coefficients for the KBC code are also suggested.

• Journal of the Korean Geotechnical Society
• /
• v.33 no.3
• /
• pp.37-47
• /
• 2017

The geotechnical characteristics of frozen ground is one of the key design issues for the construction of infrastructure in cold region. In this study, the dynamic properties (shear modulus and damping ratio) of frozen and unfrozen soils sampled from Terra Nova Bay located in eastern Antarctica, where Jang Bogo station was built, were investigated using Stokoe-type resonant column test (RC). In order to freeze the reconstituted soil specimen, the RC testing equipment was modified by adding a cooling system. A series of resonant column tests were performed in frozen and unfrozen soils with various soil densities and temperatures. The shear modulus (G) and damping ratio (D) of soil frozen at $-7^{\circ}C$ were compared with those of unfrozen soil. In addition, the effect of temperature rise on the maximum shear modulus ($G_{max}$) and damping ratio was experimentally investigated. This study has significance in that the difference of dynamic soil properties between frozen and unfrozen soils and the effect of temperature rise on frozen soil were identified.

• Journal of the Korean Society for Railway
• /
• v.15 no.5
• /
• pp.476-484
• /
• 2012

In this study, a mid-size RC test apparatus equipped with analyzing program is developed that can test samples up to D=10cm diameter and H=20cm height which is larger than usual samples of D=5cm and H=10cm used mostly in practice. Thus, crushed stones with larger grains up to 38mm in diameter used mostly in Korea as reinforced trackbed materials in track construction could be considered effectively than conventionally used RC apparatus for evaluation of the dynamic properties of the materials by using the newly developed RC apparatus. The RC test apparatus was designed and assembled based on the concept of fixed-free fixity conditions and driving mechanism proposed by Stokoe. Using the developed RC test apparatus, three types of representative crushed reinforced trackbed materials were tested in order to get the dynamic properties of the materials such as $G/G_{max}$ reduction curves and damping ratio D. For comparison purpose, a small RC test apparatus has been used to test the same materials.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.3 no.1
• /
• pp.58-63
• /
• 2015

Several researches on cement zero concrete using alkali-activators have been conducted to investigate its fundamental material properties such as slump, strength and durability, however, research on the structural behavior of relevant members involving the elastic modulus, stress-strain relationship is essential for the application of this cement zero concrete to structural members. In this paper the shear behavior of reinforced concrete beams using 50 MPa-alkali activated slag concrete was experimentally evaluated. To achieve such a goal, six reinforced concrete beam specimens were fabricated and their shear behaviors were observed. The maximum difference between test results and analysis results in crack shear stress for beam specimens without stirrups is 31%, while that for beam specimens with stirrup is 15%. Furthermore, it is also found that the shear strength of alkali activated slag concrete is by 22~57% greater than the nominal shear strength calculated by design code, implying that shear design equations would provide conservative results on the safety side.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.12 no.1
• /
• pp.29-42
• /
• 2008

The objective of this study is to investigate the effects of rigid end platens on effective stresses in soil mass during consolidation. The friction between the teeth of top cap/base pedestal and the specimen during consolidation decreases the radial and tangential effective stresses in RC specimens. However, it is unpractical to measure the effective stresses in the soil specimen. Two approaches were used to evaluate the state of stress in RC specimens during consolidation. First, careful measurements were made of small strain shear modulus, $G_{max}$ in specimens with carefully controlled void ratios and stress histories, to infer the state of stress. And second, a finite element analysis was performed to analytically evaluate the effect of various soil parameters on the state of stress in RC specimens during consolidation. By combining these experimental and analytical results, an example was performed to predict the average state of stress in RC specimens during consolidation.

• The Journal of Engineering Geology
• /
• v.32 no.1
• /
• pp.173-191
• /
• 2022

In this study, the shear wave velocity of the ground was measured using Flat TDR, and the precision analysis of the measured value and the verification of field applicability were performed. The shear wave velocity measurement value was derived in the field using the piezo-stack combined in the Flat TDR. analyzed. As a result of the experiment, the average value of the change in shear wave speed at the time of grout material injection was 10.15 m/s at the beginning of age, and the average value of the change in shear wave speed after the 7th to 14th days was 65.99 m/s, showing a tendency to increase with age. Also, it was found that dry density and shear wave speed increased as the water content increased on the dry side, and that the dry density and shear wave rate decreased as the water content increased on the wet side as the water content increased. The shear modulus value derived from the field test was confirmed to be a minimum of 17.36 MPa and a maximum of 28.13 MPa, confirming a measurement value similar to the reference value. Through this, it can be seen that the measured value of the shear modulus using Flat TDR is reliable data, and it can be determined that the compaction management of the site can be effectively managed in the future.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2008.10a
• /
• pp.1278-1284
• /
• 2008

This study carried out bender element tests in a calibration chamber in order to estimate the characteristics of soil specimen prepared in a calibration chamber. Basically, the purpose of bender element test is to measure the shear wave velocity. Bender element test cannot only confirm the status of soil specimen deposited in a chamber, but also estimate the consolidation process indirectly. In order to carry out bender element test in a calibration chamber, a pair of bender elements was installed inside the chamber, using the 'ㄷ' shaped frame. For the sandy soils having various relative densities in various stress conditions, the maximum shear modulus was estimated. From the comparison with bender element test results in a triaxial testing device, testing device and procedure was validated.