• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.853-860
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• 2011

The societal interest on a faster transportation demands an increase of the train speed over the current operation speed of 350 km/h. However, the dynamic response in the roadbed of concrete track system subjected to the train speed ranging between 300 to 500 km/h has been systematically investigated. Herein, a series of the 2-dimensional numerical simulations using various train speeds were performed. A single wheel was modeled by the rigid body. The rail was attached to the sleepers via linear springs in parallel. The results show that the vertical displacement at the rail and track concrete layer exponentially increases when the train speed increases over 400 km/h. This conclusion implies an existence of the critical train velocity at which the displacement of the track system dramatically increases.

• Geomechanics and Engineering
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• 제2권2호
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• pp.71-88
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• 2010

Soil nailing technique is being widely used for stabilization of vertical cuts because of its economic, environment friendly and speedy construction. Global stability and lateral displacement are the two important stability criteria for the soil nail walls. The primary objective of the present study is to evaluate soil nail wall stability criteria under the influence of in-situ soil variability. Finite element based numerical experiments are performed in accordance with the methodology of $2^3$ factorial design of experiments. Based on the analysis of the observations from numerical experiments, two regression models are developed, and used for reliability analyses of global stability and lateral displacement of the soil nail wall. A 10 m high prototype soil nail wall is considered for better understanding and to highlight the practical implications of the present study. Based on the study, lateral displacements beyond 0.10% of vertical wall height and variability of in-situ soil parameters are found to be critical from the stability criteria considerations of the soil nail wall.

• Structural Engineering and Mechanics
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• 제14권3호
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• pp.365-380
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• 2002

Following a series of experiments on isolated low-rise RC shear walls with openings, a theoretical study on the backbone curve of a perforated shear wall shows that there are some important observations from experimental results that make clear a semi-empirical formula of the backbone curve of a perforated wall. Critical shear zones can be depicted from the configuration of shear walls with openings. Different factors, including the size and location of shear wall openings, the wall's height/width ratio, horizontal and vertical steel bar ratios, and location and amount of diagonal steel bars are involved in the derivation of the backbone curve. Bending and shear effects are also considered in the paper. In addition, a comparison of load and displacement for solid and perforated shear walls is discussed. Generally, the comparison between experimental curves and computed backbone curves is favorable.

• 한국산업안전학회:학술대회논문집
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• 한국안전학회 1998년도 춘계 학술논문발표회 논문집
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• pp.89-97
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• 1998

In this study, under large scale yielding conditions crack propagation is found to governed by parameters based on the J-integral or on the crack opening displacement. But initiation of crack propagation of ductile material seems to be controlled by just on parameter that is the strain. The relationship between the critical value of J-integral and the local fracture strain in uniaxial tensile test in the region of maximum reduction in area. Therefore, the fundamental theorectical equation by the proposed elastic-plastic fracture toughness and the local fracture strain has a merit. in comparison with the ASTM method, which can measure by using the load-displacement curve and the specimens in tenslie test.

• 한국안전학회지
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• 제13권4호
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• pp.25-33
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• 1998

In this study, under large scale yielding conditions crack propagation is found to governed by parameters based on the J-integral or on the crack opening displacement. But initiation of crack propagation of ductile material seems to be controlled by just on parameter that is the strain. The relationship between the critical value of J-integral and the local fracture strain in uniaxial tensile test in the region of maximum reduction in area. Therefore, the fundamental theoretical equation by the proposed elastic-plastic fracture toughness and the local fracture strain has a merit, in comparison with the ASTM method, which can measure by using the load-displacement curve and the specimens in tensile test.

• 한국농공학회지
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• 제41권2호
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• pp.92-103
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• 1999

A series of field tests were performed to suggest a rational method for the stability evaluation of soft clay. The behavior of settlement-displacement obtained by field monitoring system was used to compare and analyze with various stability evaluation methods, and to investigate the applicability of the methods for stability evaluation of soft clay. The limit equilibrium method, numerical analysis and field monitoring methods were used to analyze the stability evaluation. The horizontal displacement was abruptly increased when physicla properties of soft clay reached its maximum values and therefore, the values of these properties could be used to the fundamental data for stability evaluation. The evaluation of the stability of clay embankment was suggested to use inclination of ccrve rather than critical line, and the minimum satey factor of 1.2 or larger for natural clay was recommeded . Therefore, the evaluation of short term stability of soft clay could be effectively peformed with the hypefrbolic model and the field monitored data.

• Structural Engineering and Mechanics
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• 제51권6호
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• pp.955-971
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• 2014

Large post-buckling behavior of Timoshenko beams subjected to non-follower axial compression loads are studied in this paper by using the total Lagrangian Timoshenko beam element approximation. Two types of support conditions for the beams are considered. In the case of beams subjected to compression loads, load rise causes compressible forces end therefore buckling and post-buckling phenomena occurs. It is known that post-buckling problems are geometrically nonlinear problems. The considered highly non-linear problem is solved considering full geometric non-linearity by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. There is no restriction on the magnitudes of deflections and rotations in contradistinction to von-Karman strain displacement relations of the beam. The beams considered in numerical examples are made of lower-Carbon Steel. In the study, the relationships between deflections, rotational angles, critical buckling loads, post-buckling configuration, Cauchy stress of the beams and load rising are illustrated in detail in post-buckling case.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 봄 학술발표회 논문집
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• pp.187-194
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• 1999

Laminated rubber bearings are widely used as a key component in seismic isolation of structural systems subjected to earthquake loadings. The combination of rubber layers and reinforcing steel shims makes the bearings conditionally unstable similar to buckling of ordinary columns. The shear flexibility of these short columns can lead to relatively low buckling Toads which may be further reduced when high shear strains are simultaneously imposed As an analytical approach, the area reduction formula has been proposed to account for the reduction in buckling load due to shear, but the degree of conservatism is unknown. In order to complement analytical approaches, a non-linear finite element analysis can be used. In this paper, a numerical study which aims at determining the effect of high shear strain on the critical load of elastomeric bearings is presented. From the load-displacement curve at each specified shear displacement, the buckling load can be obtained using the Southwell procedures. The results obtained are then compared against the theoretical predictions in order to examine the validity and the conservatism of the theoretical formulas.

• Nuclear Engineering and Technology
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• 제48권3호
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• pp.758-764
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• 2016

Specimens of stainless steel reactor internals were irradiated with 240 keV protons and 6 MeV Xe ions at room temperature. Nanoindentation constant stiffness measurement tests were carried out to study the hardness variations. An irradiation hardening effect was observed in proton- and Xe-irradiated specimens and more irradiation damage causes a larger hardness increment. The Nix-Gao model was used to extract the bulk-equivalent hardness of irradiation-damaged region and critical indentation depth. A different hardening level under H and Xe irradiation was obtained and the discrepancies of displacement damage rate and ion species may be the probable reasons. It was observed that the hardness of Xe-irradiated specimens saturate at about 2 displacement/atom (dpa), whereas in the case of proton irradiation, the saturation hardness may be more than 7 dpa. This discrepancy may be due to the different damage distributions.

• Structural Engineering and Mechanics
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• 제28권4호
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• pp.357-372
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• 2008

This study investigates effect of uncertainty in natural vibration period on the seismic demand. It is shown that since this uncertainty affects the acceleration and displacement responses differently, two ratios, one relating peak acceleration responses and the other relating the peak displacement responses, are not equal and both must be employed in evaluating and defining the critical seismic demand. The evaluation of the ratios is carried out using more than 200 strong ground motion records. The results suggest that the uncertainty in the natural vibration period impacts significantly the statistics of the ratios relating the peak responses. By using the statistics of the ratios, a procedure and sets of empirical equations are developed for estimating the probability consistent seismic demand for both linear and nonlinear systems.