• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.1
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• pp.105-111
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• 2013

The spindle is the main component in machine tools. The static and dynamic characteristics of the spindle directly affect the machining accuracy of workpieces. The characteristics of the spindle depend on the shaft size, bearing span, built-in motor location, and so on. Therefore, the appropriate selection of these parameters is important to improve the spindle characteristics. This paper presents the analysis of the static and dynamic characteristics and optimization design of a 40,000-rpm high-speed spindle. Statistical analysis for optimization and finite element analysis were performed. This study uses the response surface method to optimize the objective function and design factors. The targets are the natural frequency and displacement. The design factors are the shaft length, shaft diameter, bearing span, and motor location. The optimized design provides better results than the initial model, and these results are expected to improve the static and dynamic characteristics of the spindle.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.6
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• pp.283-291
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• 2018

This study intends to develop an analytical model of unreinforced masonry(URM) walls for the nonlinear static analysis which has been generally used to evaluate the seismic performance of a building employing URM walls as seismic force-resisting members. The developed model consists of fiber elements used to capture the flexural behavior of an URM wall and a shear spring element implemented to predict its shear response. This paper first explains the configuration of the proposed model and describes how to determine the modeling parameters of fiber and shear spring elements based on the stress-strain curves obtained from existing experimental results of masonry prisms. The proposed model is then verified throughout the comparison of its nonlinear static analysis results with the experimental results of URM walls carried out by other researchers. The proposed model well captures the maximum strength, the initial stiffness, and their resulting load - displacement curves of the URM walls with reasonable resolution. Also, it is demonstrated that the analysis model is capable of predicting the failure modes of the URM walls.

• Composites Research
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• v.34 no.2
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• pp.101-107
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• 2021

Composite structures have components and joints. Theses connections or joints can be potentially weak points in the structure. The failure mode of the composite bolted joint is designed as a bearing failure mode for structural safety. The load-displacement relation exhibits bearing failure mode shows a nonlinear behavior after the initial failure and progressive failure behavior. In order to accurately predict the failure behavior of composite bolted joints, this study modified the shear damage variable calculation process in the existing progressive failure analysis model. The results of the bearing stress-bearing strain of the composite bolted joint were predicted using the modified progressive failure analysis model, and the modified model was verified through comparison with the previous progressive analysis model.

• Journal of the Korean Wood Science and Technology
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• v.31 no.5
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• pp.96-103
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• 2003

This study was conducted to evaluate the tensile properties of metal plate connector for the domestic major softwoods, such as Korean red pine, Korean white pine, and Japanese larch. The maximum tensile load of Korean red pine was 3,612kgf in AA type, it was 1.2 and 1.7 times higher load than that of Japanese larch and Korean white pine. In EA type, it was 2,704kgf, and 1.1 and 1.5 times higher than the loads of Japanese larch and Korean white pine. The failure modes of metal plate connector were metal plate withdrawal, plate tensile failure, and wood shear block failure. The failure mode of Korean red pine connector was tensile failure of plate, that is reason of the high tensile load resistance for metal plate connections in Korean red pine. The mechanical properties of metal plate connector could be predicted by the Foschi model parameter. In the initial stage, the Korean red pine connector was stiffer than the other species. The design values for metal plate connector per tooth was 25, 22, and 15kgf for Korean red pine, Japanese larch, and Korean white pine in AA type and 19, 17, and 13kgf in EA type.

• Journal of the Korean Geotechnical Society
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• v.23 no.5
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• pp.89-100
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• 2007

In this study, various field and laboratory tests were performed to investigate the characteristics of shear strength and bearing behavior to be considered in the estimation of stability and trafficability in early stage of stabilization process in marine clay dredged deposit. Site characterization was carried out to grasp the basic properties of the deposit. Field vane test, unconfined compression test and direct shear test were conducted to evaluate the shear strength distribution for varied depths, and the characteristics of shear strength and stress-strain behavior of the crust layer. Plate load tests were also performed to estimate the bearing capacity and to assess load-settlement behavior and failure pattern of the deposit. The bearing capacity was also estimated using previously proposed methods for double-layered clay deposit. The estimated bearing capacity was compared with the results of the plate load tests and then, the applicability of the estimation method was discussed.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.2
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• pp.105-116
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• 2010

The estimation of surface settlement, ground behavior and tunnel displacement are the main factors in urban tunnel design with shallow depth and unconsolidated soil. On deformation analysis of shallow tunnel, it is important to identify possible deformation mechanism of shear bands developing from tunnel shoulder to the ground surface. This paper investigated the effects of key design parameter affecting deformation behavior by numerical analysis using nonlinear model incorporating the reduction of shear stiffness and strength parameters with the increment of the maximum shear strain after the initiation of plastic yielding. Numerical parametric studies are carried out to consider the reduction of shear stiffness and strength parameters, horizontal stress ratio, cohesion and shotcrete thickness.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.187-196
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• 2008

The punching shear strength of RC slabs is estimated analytically by the simple truss model. To avoid intrinsic difficulties in punching shear analysis of reinforced concrete slabs, the slabs were divided into three sub-structures as the punching cone and the remaining parts. The strength of the punching cone was evaluated by the stiffness of inclined strut. The stiffness of springs which control lateral displacement of the roller supports consists of the steel reinforcement which passed through the punching cone. Initial angle of struts was determined by curve fitting method of the experimental data with variable reinforcement ratio in order to compensate for uncertainties in the slab's punching shear, the simplification errors and the stiffness of the remaining sub-structures. The validity of computed punching shear strength by simple truss model was shown by comparing with experimental results. The punching shear strength, which was determined by snap-through critical load of shallow truss, can be used effectively to examine punching shear strength of RC slabs.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.21-33
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• 2006

The reliability analysis can be conducted more effectively by formulating the stochastic finite element method suitable for the reliability theory about the cable stayed bridge. After conducting the initial equilibrium analysis of the cable stayed bridge, the program which can conduct the linear and nonlinear stochastic finite element analysis using the perturbation method and the reliability analysis considered to the correlation of the random variable is developed. Using the results of this program about the cable stayed bridge, the characteristic of the node displacement, element force and cable tension according to the correlation of the random variable is investigated quantitatively. Also the reliability index and the failure probability are examined by the compounding the correlation of the random variable.

• Journal of the Korean Geotechnical Society
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• v.24 no.4
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• pp.101-114
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• 2008

Pressurized grouting is a common technique in geotechnical engineering applications to increase the stiffness and strength of the ground mass and to fill boreholes or void space in a tunnel lining and so on. Recently, the pressurized grouting has been applied to a soil-nailing system which is widely used to improve slope stability. Because interaction between pressurized grouting paste and adjacent ground mass is complicated and difficult to analyze, the soil-nailing design has been empirically performed in most geotechnical applications. The purpose of this study is to analyze the ground behavior induced by pressurized grouting paste with the aid of laboratory model tests. The laboratory tests are carried out for four kinds of granitic residual soils. When injecting pressure is applied to grout, the pressure measured in the adjacent ground initially increases for a while, which behaves in the way of the membrane model. With the lapse of time, the pressure in the adjacent ground decreases down to a value of residual stress because a portion of water in the grouting paste seeps into the adjacent ground. The seepage can be indicated by the fact that the ratio of water/cement in the grouting paste has decreased from a initial value of 50% to around 30% during the test. The reduction of the W/C ratio should cause to harden the grouting paste and increase the stiffness of it, which restricts the rebound of out-moved ground into the original position, and thus increase the in-situ stress by approximately 20% of the injecting pressures. The measured radial deformation of the ground under pressure is in good agreement with the expansion of a cylindrical cavity estimated by the cavity expansion theory. In-situ test revealed that the pullout resistance of a soil nailing with pressurized grouting is about 36% larger than that with regular grouting, caused by grout radius increase, residual stress effect, and/or roughness increase.

• The korean journal of orthodontics
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• v.31 no.3 s.86
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• pp.311-323
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• 2001

One of the various mechanics used to treat unilateral Class II malocclusion is head gear with asymmetric face bow. We made the finite element models of unilateral Class II maxillary dental arch and power arm asymmetric face bow. We designed this experiment to observe stress distribution of periodontal ligament, reaction force, and displacement and to understand force system, so to predict the therapeutic effect. On the basis of computerized tomograph of maxillary dental arch of 25 years old male with normal occlusion without extraction and orthodontic treatment history, we made finite element models of maxillary dental arch and periodontal ligament. Then we modified that model to unilateral maxillary Class II malocclusion model of which maxillary left molar displaced mesially. Also, We made finite element model of asymmetric face bow of which right outer bow shorter than left by 25mm(RMO, Penta-FormTM/Medium size, 0.045 inch iner bow, 0.072 inch outer bow). After that, retraction force of 250g, 300b, 350g were applied to maxillary first molar. We concluded as follow. 1. The Net force that both maxillary first molars were received increased as the retraction force increased. Mesially positioned tooth received more force than normally positioned tooth. But, both tooth were received distal force, so distal movement occured. 2. Both tooth received buccal lateral force. In analysis of force element, as the retraction force were increased, force of X-axis at mesially positioned tooth decreased, and force of X-axis at normally positioned tooth increased. so lateral force component moved to the side received less force from more force. 3. There were rotation, tipping with distal movement in maxillary first molar. As retraction force were increased, rotation and tipping also increased. More tipping and rotation occured at the side received more force, that is, mesially positioned tooth. Though it Is small change, displacement of same pattern occur in normally positioned tooth