• The korean journal of orthodontics
• /
• v.32 no.5 s.94
• /
• pp.343-353
• /
• 2002

This study was designed to investigate the stress distribution of alveolar bone in case of on masse retraction with lingual K-loop archwire using the 3-dimensional photoelastic stress analysis followed by stress freezing process. Lingual K-loop archwire which had loop in 15mm height was used and activated by retraction force of 350gm per each side. The results were as follows 1. Central incisor : As the closer side to crown, the larger tensile stress was distributed at both mesial and labial surfaces and the larger compressive stress was distributed at distal surface. As the closer side to root apex, the larger compressive stress was distributed at lingual surface. The compressive stress was distributed at root apex. 2. Lateral incisor : The tensile stress was distributed at the coronal side of mesial surface. The compressive stress was distributed at distal surface. As the closer side to crown, the larger tensile stress was distributed at labial surface. The tensile stress was distributed at coronal side and the compressive stress was distributed at apical side of lingual surface. The compressive stress was distributed at root apex. 3. Canine The tensile stress was distributed at coronal side and the compressive stress was distributed at apical side of mesial surface. The tensile stress was distributed at distal surface. As the closer side to crown, the larger tensile stress was distributed at both mesial and distal surfaces. The compressive stress was distributed at root apex. 4. Second premolar : The tensile stress was distributed at mesial surface. The compressive stress was distributed at coronal side and the tensile stress was distributed at apical side of distal surface. The compressive stress was distributed at coronal side of buccal surface. As the closer side to crown, the larger tensile stress was distributed at lingual surface. The compressive stress was distributed at root apex. 5. First molar . As the closer side to crown, the larger tensile stress was distributed at both mesial and distal surfaces. No stress was distributed at buccal surface and palatal root apex. As the closer side to crown, the larger tensile stress was distributed at both lingual surfaces. The compressive stress was distributed a4 buccal root apexes. 6. Second molar The compressive stress was distributed at all root apexes. As the closer side to crown, the larger compressive stress was distributed at both mesial and lingual surfaces, and the larger tensile stress at both distal and buccal surfaces. Transverse bowing effect was observed in on-masse retraction with lingual K-loop archwire, however vertical towing effect was not. Rather, reverse vortical bowing effect was developed.

• Tunnel and Underground Space
• /
• v.17 no.1 s.66
• /
• pp.26-31
• /
• 2007

The 11 nuclear power plants have been taking charge of more than 40% of the total electrical power development in Korea. In addition to the existing nuclear power plants at Gori, Wolsung, Youngkwang, etc., the 12 nuclear power plants are expected to be newly established until 2006. So, the 23 nuclear power plants will produce the electric power as much as more than 50% of the national gross production. However the nuclear power plants are inevitably generating the detrimental atomic wastes. Therefore the disposal techniques for the nuclear wastes should be ensured considering a very high safety factor. According to the basic researches in KAERI, the underground disposal repositories are reported to be most favorable for Korea. The KBS-3 disposal system has been strongly suggested by KAERI and this system has a deep tunnel with several disposal boreholes in tunnel floor. The nuclear wastes, which are sealed tightly in a canister, will be disposed in these boreholes. Considering the disposal tunnel in a great depth, the in-situ stress regimes will affect severely the tunnel stability. Consequently the effect of the in-situ stresses on the disposal tunnel and the role of the in-situ stresses in tunnel stability analysis are examined by the numerical studies.

• Journal of the Korea Concrete Institute
• /
• v.14 no.3
• /
• pp.331-340
• /
• 2002

In this paper, finite element analysis is applied for simulation of cracks due to restraining autogenous and drying shrinkage at early-age concrete. A micro-level heat hydration model and a shrinkage prediction model along with a moisture diffusion model are adopted for the finite element analysis. Then, an axial restraint test is carried out for concrete specimens containing different amounts of chloride ions to evaluate stress development and cracking due to the restraining shrinkages at early ages. Test results show that the increase of contents of chloride ions increases restrained stress, but does not increase strength. By this increase of shrinkage strain at early-age, time to occur the crack is accelerated. Finally, stress development and cracking of concrete specimens containing different amount of chloride ions we simulated using the finite element analysis. Results of the analysis using the Proposed model are verified by comparison with test results.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.38 no.1
• /
• pp.1-10
• /
• 2018

It is difficult to predict the early-age cracks of strain restrained concrete members due to environmentally sensitive parameters. A new method is proposed to predict the cracks by test of autogenous deformation and self-induced restrained stress of specimens which simulates early-age crack state by hydration heat of the'Wall-On-Foundation'members. For this purpose, thermal analysis of entire structure considering the environmental condition is performed at first, and the specimens are set up where hydration heat was electronically controlled according to the analysis results. By measuring free deformation and force to compensate the autogenous strain including relaxation, feasibility of cracks can be estimated. The proposed method can predict the occurrence of cracks better than the material test of the early age concrete which has large variance. The method of this study is particularly useful when it is used as a preliminary experiments to predict the crack more precisely before full-scale concrete placement in construction of large structures.

• Proceedings of the Korean Society for Rock Mechanics Conference
• /
• 2001.03a
• /
• pp.251-258
• /
• 2001

• Tunnel and Underground Space
• /
• v.1
• /
• pp.91-101
• /
• 1991

• Journal of the Korea Concrete Institute
• /
• v.13 no.5
• /
• pp.447-456
• /
• 2001

Many investigators have tried to represent the nonlinear behavior of stress-strain relationship of concrete using mathematical curves. Most of empirical expressions for stress-strain relationship, however, have focused on old age concrete, and were not able to represent well the behavior of concrete at an early age. Where wide understanding on the behavior of concrete from early age to old age is very important in evaluating the durability and service life of concrete structures. In this paper, effect of 5 different strength levels and ages of from 12 hours to 28 days on compressive stress-strain relationship was observed experimentally and analytically. Tests were carried out on $\phi$100${\times}$200mm cylindrical specimens water-cured at 20${\pm}$3$^{\circ}C$. An analytical expression of stress-stain relationship with strength and age was developed using regression analyses on experimental results. For the verification of the proposed model, the model was compared with present and existing experimental data and some existing models. The analysis shows that the proposed model predicts well experimental data and describes well effect of strength and age on stress-strain relationship.

• Proceedings of the Korean Society of Disaster Information Conference
• /
• 2016.11a
• /
• pp.188-189
• /
• 2016

본 논문은 초기하중을 하중을 받는 역대칭 angle-ply 와 cross-ply 적층판의 좌굴 및 진동특성을 무재하시의 고유진동수를 이용하여 산정하는 간편법을 제시하였다. 마주보는 두변이 단순 지지된 역대칭 적층판의 운동방정식은 전단변형과 회전강성효과를 고려한 YSN 이론으로 유도하였으며 이를 선점법을 이용하여 해석하였다. 초기응력을 받는 적층판의 무차원화 고유진동수, 임계좌굴계수 및 동적 주 불안정영역 문제들을 무재하시의 무차원화 고유진동수로서 각각의 특성을 정립시켰다. 본 연구에서 제안한 진동특성에 관한 간편산정식의 정당성과 사용성을 입증하기 위하여 수치예들로서 검토하였다.

• Journal of the Korea Concrete Institute
• /
• v.22 no.3
• /
• pp.427-435
• /
• 2010

One of the most vulnerable properties in concrete is tensile cracking, which usually happens at early ages due to hydration heat and shrinkage. In order to accurately predict the early age cracking, it needs to find out how stress-crack opening relation is varying over time. In this study, inverse analyses were performed with the existing experimental data for wedge-splitting tests, and the parameters of the softening curve for the stress-crack opening relation were determined from the best fits of the measured load-CMOD curves. Based on the optimized softening curve, variation of fracture energy over time was first examined, and a model for the stress-crack opening relation at early ages was suggested considering the found feature of the fracture energy. The model was verified by comparisons of the peak loads, CMODs at peak loads, and fracture energies obtained from the experiments and the inverse analysis.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.12 no.4
• /
• pp.642-651
• /
• 1988

The present paper develops finite element procedures to calculate displacements, strains and stresses in initially stressed elastic solids subjected to static or time-dependent loading conditions. As a point of departure, we employ Hamilton's principle to obtain nonlinear equations of motion characterizing the displacement in a solid. The equations of motion reduce to linear equations of motion if incremental stresses are assumed to be infinitesimal. In the case of linear problem, finite element solutions are obtained by Newmark's direct integration method and by modal analysis. An analytic solution is referred to compare with the linear finite element solution. In the case of nonlinear problem, finite element solutions are obtained by Newton-Raphson iteration method and compared with the linear solution. Finally, the effect of the order of Gauss-Legendre numerical integration on the nonlinear finite element solution, has been investigated.