• Journal of Korean Tunnelling and Underground Space Association
• /
• v.21 no.6
• /
• pp.861-874
• /
• 2019

A great interest in the seismic performance evaluation of small size tunnel structures such as utility tunnel has been taken since recent earthquakes at Pohang and Gyeongju in Korea. In this study, the three-dimensional dynamic analyses of vertical shaft and horizontal tunnel under seismic load were carried out using FLAC3D. Especially, parametric analyses was performed to investigate the effects of interfacial stiffness on interfacial behavior between soil and structure. The parametric analysis showed that the interfacial stiffness scarcely gave an effect on the global dynamic behavior of the structure, while had a significant effect on the local displacement behavior of the connections. The magnitude of the interfacial stiffness was inversely proportional to the displacement, while the magnitude of interface stiffness was proportional to the normal and shear stresses. The results of this study suggest the limitations of the existing empirical equations for interfacial stiffness and emphasize the need to develop new interfacial stiffness models.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.6
• /
• pp.97-102
• /
• 2007

Though the stability analysis of soil slopes widely employs the limit equilibrium method, the study on the jointed rock slopes must consider the direction of joint and the characteristics of Joint at the same time. This study analyzes the result of the change in the factors which show the characteristics of discontinuity and the shape factor of rock slopes, and so on, in an attempt to validate the propriety as to the interpretation of jointed rock slope stability which uses the general finite element program. First, the difference depending on the flow rules was compared, and the factor effect study was conducted. The selected independent variables included the direction of joint which displays the mechanical characteristics of discontinuity, adhesive cohesion, friction angle, the inclination and height of rock slope which reveal the shape of slope and surcharge load. And the horizontal displacement was numerically interpreted at the 1/3 point below the slope, a dependent variable, to compare the relative degree of factor effects. The findings of study on factor effects led to the validation that the result of horizontal displacement for each factor satisfied various engineering characteristics, making it possible to be applied to stability interpretation of jointed rock slope. A modelling is possible, which considers the application of the result of real geotechnical surveys & laboratory studies and the non-linear characteristics when designing the rock slope. In addition, the stress change which may result from the natural disaster, such as precipitation, and the construction, can be expressed. Furthermore, as the complicated rock condition and the ground supporting effect can be considered through FEM, it is considered to be very useful in making an engineering decision on the cut-slope, reinforcement and so on.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.36 no.2
• /
• pp.70-79
• /
• 2020

Purpose: The purpose of this study was to evaluate the effect of attachments and palatal coverage on stress distribution in maxillary implant overdenture using finite element analysis. Materials and Methods: Four maxillary overdenture 3-D models with four implants placed in the anterior region were fabricated with computer-aided design. 1) Ball-F: Non-splinted ball attachment and full palatal coverage, 2) Ball-P: Non-splinted ball attachment and U-shaped partial palatal coverage, 3) Bar-F: Splinted milled bar attachment and full palatal coverage, 4) Bar-P: Splinted milled bar attachment and U-shaped partial palatal coverage. Stress distribution analysis was performed with ANSYS workbench 14. 100 N vertical load was applied at the right first molar unilaterally and maximum stress was calculated at the implant, peri-implant bone and mucosa. Results: The use of the ball attachment showed lower maximum stress on implant and peri-implant bone than the use of the milled bar attachment. But it showed contrary tendency in the mucosa. Regardless of attachment, full palatal coverage showed lower maximum stress on implant, peri-implant bone and mucosa. Conclusion: Within the limitation of this study, ball attachment improved stress distribution on implant and peri-implant bone rather than milled bar attachment in maxillary implant overdenture. Also, full palatal coverage is more favorable in stress distribution.

• Journal of Korean Association for Spatial Structures
• /
• v.4 no.2 s.12
• /
• pp.89-97
• /
• 2004

The objective of this study is the development of a scheme and discrete optimum design algorithm, which is based on the genetic algorithm. The algorithm can perform both scheme and size optimum designs of plane trusses. The developed Scheme genetic algorithm was implemented in a computer program. For the optimum design, the objective function is the weight of structures and the constraints are limits on loads and serviceability. The basic search method for the optimum design is the genetic algorithm. The algorithm is known to be very efficient for the discrete optimization. However, its application to the complicated structures has been limited because of the extreme time need for a number of structural analyses. This study solves the problem by introducing the size & scheme genetic algorithm operators into the genetic algorithm. The genetic process virtually takes no time. However, the evolutionary process requires a tremendous amount of time for a number of structural analyses. Therefore, the application of the genetic algorithm to the complicated structures is extremely difficult, if not impossible. The scheme genetic algorithm operators was introduced to overcome the problem and to complement the evolutionary process. It is very efficient in the approximate analyses and scheme and size optimization of plane trusses structures and considerably reduces structural analysis time. Scheme and size discrete optimum combined into the genetic algorithm is what makes the practical discrete optimum design of plane fusses structures possible. The efficiency and validity of the developed discrete optimum design algorithm was verified by applying the algorithm to various optimum design examples: plane pratt, howe and warren truss.