• Journal of the Korean Geotechnical Society
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• v.23 no.3
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• pp.41-50
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• 2007

The results from normally consolidated isotropic drained and undrained triaxial compression tests (NCIU and NCID) on sand with high silt content were presented in this paper. The experiments were performed on specimens of Nak-dong River sand with 63% silt content under effective confined pressures, 100 kPa to 400 kPa. From test results, Sandy silt became initially compressive but eventually appeared to provide dilatancy response throughout the entire stress-strain curve The behavior of sandy silt was more difficult to characterize than that of clay and sand due to lower plastic characteristic. Especially, the samples exhibited dilatancy development during shear after failure. The shear behavior and shear strength parameters of sandy silt can be determined as stress-strain behaviors are described by the Mohr-Coulomb failure criterion. The shear behaviors were observed increasing dilatancy volume change tendency with strain-softening tendency after failure. In this paper, the behavior of dilatancy depends on not only sand content but also fine content with low-cohesion during shear in the samples of sandy silt.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.5
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• pp.101-112
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• 2011

This paper shows a study carried out on the estimation of nominal flexural strength for CFRP-plated RC beams failed by intermediate crack debonding. A strength reduction factor is proposed to consider the effect of the intermediate crack debonding for the determination of nominal flexural strength. The proposed factor is derived from experimental data and utilizes the ratio of effective stress(or strain) in the CFRP plate to its ultimate strength(or strain) which is called effective strain model. An analytical equation for the estimation of the nominal flexural strength is formulated as a function of strength reduction factor. The validity, accuracy and efficiency of the proposed factor are established by comparing the analytical results with the experimental data, and the major design codes, as well as a number of factors given by researchers. The analytical results presented in this paper indicate that the proposed factor can effectively estimate the flexural nominal strength of CFRP-plated reinforced concrete beams failed by intermediate crack debonding.

• Geotechnical Engineering
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• v.13 no.6
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• pp.139-146
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• 1997

The failure of footing generally involves the concentration of deformation into one or more narrow bands. With the displacement of the footing, the failure plane will subsequently form The purpose of this paper is to assess the capabilities of numerical techniques to predict bearing capacity and progressive failure of footings. By using the method of large deformation theory and strain softening we have investigated the progressive failure of strip footing on undrained clay. This paper describes the procedure to predict the entire loadfisplacement curve and the failure mechanism of strip footing. The presented results show that it is Possible to analyze the Post Peak behavior of strip footing numerically and to give a progressive failure mechanism clearly.

• Journal of the Korea Concrete Institute
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• v.15 no.1
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• pp.69-77
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• 2003

One directional and biaxial tension tests of 13 reinforced concrete panels were conducted to derive a constitutive law of concrete. Based on the test results, a model equation is derived for the stress-strain relationship of concrete in tension. Main test variables are reinforcement ratio and the load ratio applied in two directions. In addition a failure envelope of concrete in tension-tension region is suggested based on the initial crack occurrence. Test results show that the concrete carries substantial tensile stress even after cracking occurrence. However, the application of this proposed stress-strain relationship for concrete is limited to the case where the direction of reinforcement coincides with the direction of the applied principal stresses.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.6
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• pp.573-579
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• 2016

Studies on the deformation behavior of materials subjected to impact loads have been carried out in various fields of engineering and industry. The deformation and fracture of members for these machines/structures are known to correspond to the intermediate strain-rate region. Therefore, for the structural design, it is necessary to consider the dynamic deformation behavior in these intermediate strain-rate ranges. However, there have been few reports with useful data about the deformation and fracture behavior at intermediate strain-rate ranges. Because the intermediate strain-rate region is located between quasi-static and high strain-rate regions, it is difficult to obtain the intermediate strain-rate using conventional reasonable test equipment. To solve this problem, in this study, the measurement reliability of the constructed drop-bar impact tensile test apparatus was established and the dynamic behavior at the intermediate strain-rate range of carbon steels was evaluated by utilizing the apparatus.

• Journal of the Korean Geotechnical Society
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• v.16 no.4
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• pp.95-105
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• 2000

Anisotropy of stiffiness, from extremely small strains to post-failure strains, of isotropically consolidated air-pulviated sands in plane strain compression was studied by using the newly developed instrumentation for small strain measurements. Seven types of sand of the world-wide origins were tested, which have been extensively used for research purposes. Stress-strain relationships for a wide range of strain from about 0.0001% to 10% were obtained with measuring axial and lateral strains locally free from the effects of bedding and membrane penetration errors at the specimen boundaries. It was found that the maximum shear modulus Gmax was irrespective of the angle $\delta$of the $\sigma$1 direction relative to the bedding plane. However, the normalized Gmax was varied with the types of sand. Furthermore, the dependency of the strain and stress level on the stiffness increased as decreased.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.8
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• pp.2431-2435
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• 1996

In order to determine the effects of hydrostatic pressure on the mechanical behavior of graphite fiber reinforced composites, the modulus, fracture stress(maximum stress), and fracture strain of graphite/epoxy composites have been determined as a function of pressure. Composite specimens used in this study were 90-deg unidirectional and had a 60% fiber volume fraction. Compressive tests under five different pressure levels were conducted. The result showed the modulus measured from as initial slope of stress-strain curve increased bilinearly with pressure with a break at 200 MPa. It was also found that fracture stress and fracture strain increased in a linear fashion with pressure.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.5
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• pp.144-152
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• 2007

This study investigated the failure mechanism of RC beams strengthened with AFRP sheets. Total 5 half-scale RC beams were constructed and tested to estimate the effectiveness of various methods to prevent the debonding failure of AFRP sheets. From the experimental results, it was found that increasing bonded length or end U-wrappings does not prevent debonding failure. On the other hand, the beams with center U-wrappings and shear-keys reached the ultimate state with their sufficient performance. The center U-wrappings tended to control debonding of the longitudinal AFRP sheets because the growth of the longitudinal cracks along the edges of the composites was delayed. In case of shear-keys, it was sufficient to eliminate debonding and the beams failed by AFRP sheets rupture due to the sufficient bond mechanism.

• Tunnel and Underground Space
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• v.28 no.3
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• pp.277-291
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• 2018

LSTM (Long Short-Term Memory) algorithm which is a kind of recurrent neural network was used to establish a model to predict the stress-strain curve of an material under uniaxial compression. The model was established from the stress-strain data from uniaxial compression tests of silica-gypsum specimens. After training the model, it can predict the behavior of the material up to the failure state by using an early stage of stress-strain curve whose stress is very low. Because the LSTM neural network predict a value by using the previous state of data and proceed forward step by step, a higher error was found at the prediction of higher stress state due to the accumulation of error. However, this model generally predict the stress-strain curve with high accuracy. The accuracy of both LSTM and tangential prediction models increased with increased length of input data, while a difference in performance between them decreased as the amount of input data increased. LSTM model showed relatively superior performance to the tangential prediction when only few input data was given, which enhanced the necessity for application of the model.

• Computational Structural Engineering
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• v.17 no.3
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• pp.22-27
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• 2004