• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2006년도 학술발표회 논문집
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• pp.233-240
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• 2006

An experimental investigation on the behavior of reinforced concrete coupling beams is presented. The test variables are the span-to-depth ratio, the ratio of flexural reinforcement and the ratio of shear rebar. The distribution of arch action and truss action which compose the mechanism of shear resistance is discussed. This study proposes the deformation model for reinforced concrete coupling beams considering the bond slip of flexural reinforcement. The yielding of flexural reinforcements determines yielding states and the ultimate states of reinforced concrete coupling beam are defined as the ultimate compressive strain of struts and the degradation of compressive strength due to principal tensile strain of struts. It is expected that this model can be applied to displacement-based design methods.

• Structural Engineering and Mechanics
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• 제85권3호
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• pp.337-351
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• 2023

In this paper, the shear behavior of soft filling in rectangular-hollow concrete specimens was simulated using the 2D particle flow code (PFC2D). The laboratory-measured properties were used to calibrate some PFC2D micro-properties for modeling the behavior of geo-materials. The dimensions of prepared and modeled samples were 100 mm×100 mm. Some disc type narrow bands were removed from the central part of the model and different lengths of bridge areas (i.e., the distance between internal tips of two joints) with lengths of 30 mm, 50 mm, and 70 mm were produced. Then, the middle of the rectangular hollow was filled with cement material. Three filling sizes with dimensions of 5 mm×5 mm, 10 mm×5 mm, and 15 mm×5 mm were provided for different modeled samples. The parallel bond model was used to calibrate and re-produce these modeled specimens. Therefore, totally, 9 different types of samples were designed for the shear tests in PFC2D. The shear load was gradually applied to the model under a constant loading condition of 3 MPa (σc/3). The loading was continued till shear failure occur in the modeled concrete specimens. It has been shown that both tensile and shear cracks may occur in the fillings. The shear cracks mainly initiated from the crack (joint) tips and coalesced with another one. The shear displacements and shear strengths were both increased as the filling dimensions increased (for the case of a bridge area with a particular fixed length).

• 콘크리트학회논문집
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• 제26권2호
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• pp.159-169
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• 2014

이 연구에서는 철근콘크리트 전단벽의 횡하중 거동과 연성을 합리적으로 평가하기 위해서 모멘트-곡률관계를 정립하고 이로부터 단순화된 횡하중-횡변위관계를 제시하였다. 최초 휨 균열, 인장철근 항복, 최대내력, 최대내력의 80% 및 인장철근파단시점에서 모멘트와 곡률은 힘의 평형조건과 변형적합조건으로부터 정립되었다. 최대내력 이후의 곡률평가를 위한 압축측연단 콘크리트 변형률은 Razvi and Saatcioglu의 구속된 콘크리트의 응력-변형률 관계를 이용하여 최대응력의 감소계수와 횡보강근 체적지수의 함수로 제시하였다. 모멘트 평가모델은 변수연구를 통하여 인장철근지수, 수직철근지수 및 축력지수의 함수로 일반화하였다. 횡변위는 전단벽의 높이에 따라 분포된 이상화된 곡률로부터 모멘트 면적법을 이용하여 환산하였다. 제시된 횡하중-횡변위관계는 기존 실험 결과와 잘 일치하였으며, 특히 최대내력 이후의 거동을 잘 평가하였다.

• Restorative Dentistry and Endodontics
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• 제26권1호
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• pp.41-50
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• 2001

The purpose of this study was to examine the influences of camphoroquinone on the properties of five experimental composites. The contents of camphoroquinone were varied as 0.2%, 0.3%, 0.4%, 0.5%, and 0.6%, with silanized filler 75% and tertiary amine 0.2%. Five kinds of experimental composites were prepared, and diametral tensile strength, shear bond strength, depth of cure and yellowish discoloration were tested as a measurement. Specimen numbers of 10 were applied to all test items and experimental groups. Specimens for testing the diametral tensile strengths with internal diameter of 6mm in diameter and 3mm in height were filled with 5 experimental composites which were crushed with 1mm/min cross-head speed on Instron universal testing machine (Model No. 4467). Shear bond strength was measured on specimens attached to bovine teeth enamel etched with 37% phosphoric acid. Depth of cure was measured by the measurement of height of specimens which were removed the un-polymerized portion with acetone. Yellowness measurements were made by chromometer(Minolta Co. Japan) using L$^*$a$^*$b$^*$ values. ANOVA and Multiple range tests were used analyzed data with confidence level at 95%. The mean value of the shear bond strengths ranged from 31.03MPa to 39.49MPa. Following results were obtained ; 1. Diametral tensile strength was highest in experimental group 3, then was not affected by the contents of camphoroquinone ($r^2$=0.0422). 2. Composite resins containing 0.4% camphoroquinone showed the highest shear bond strength, but there was no statistical significance (p=0.3718). 3. Camphoroquinone reduces the depth of cure in the composite resins (p=0.0004, $r^2$=0.9483). 4. Camphoroquinone made the composites yellowish ($r^2$=0.9815). These results mean that increased content of camphoroquinone reduces the depth of cure, and that camphoroquinone make composites yellowish.

• Structural Engineering and Mechanics
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• 제55권5호
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• pp.953-964
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• 2015

A model has been proposed that can predict the ultimate torsional strength of single-box multi-cell reinforced concrete box girder under combined loading of bending, shear and torsion. Compared with the single-cell box girder, this model takes the influence of inner webs on the distribution of shear flow into account. According to the softening truss theory and thin walled tube theory, a failure criterion is presented and a ultimate torsional strength calculating procedure is established for single-box multi-cell reinforced concrete box girder under combined actions, which considers the effect of tensile stress among the concrete cracks, Mohr stress compatibility and the softened constitutive law of concrete. In this paper the computer program is also compiled to speed up the calculation. The model has been validated by comparing the predicted and experimental members loaded under torsion combined with different ratios of bending and shear. The theoretical torsional strength was in good agreement with the experimental results.

• Restorative Dentistry and Endodontics
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• 제23권1호
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• pp.163-174
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• 1998

The purpose of this study is to evaluate the distribution of stress in the root end resected teeth. The finite element method was used to compare stresses along the root and retrograde filling material in seven two-dimensional models of mandibular 2nd premolar. Each model was endodontic treatment and gold crown' restoration. Each model divided with amagam core restoration or gold casting post restoration. Thus each model divided with shape of root end resection, depth of retropreparation and exposure length of root in the bony cavity. The seven models were classified as in the table 1 below. A load of 500N was applied $45^{\circ}$ diagonally on the lingual slope of the buccal cusp. These mode were analyzed with two dimensional finite element methods. The results of this study were as follows : 1. The maximum tensile stress along the inner canal wall was shown on the model 7. 2. When the model 1 was compared with the model 5, the maximum tensile stress along the inner canal wall showed the model 1. 3. Less equivalent stress was shown on the model 6 and more equivalent stress was shown on the model 4. 4. More shear stress was shown on the retrograde filling material of the model 7. 5. The models with increased length of exposed root in the bony cavity demonstrated a gradual increase to the tensile stress in X direction which occurred approximately a boundary between the bone and exposed root in' the bony cavity. 6. The model which had a case of matching the apex of post and a boundary between the bone and exposed root in the bony cavity demonstrated more increase tensile stress in X direction than other models.

• Structural Engineering and Mechanics
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• 제42권6호
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• pp.867-882
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• 2012

Analytical (Rayleigh-Ritz method) and numerical studies are carried out and buckling interaction curves are developed for simply supported plates of varying aspect ratios ranging from 1 to 5, under the combined action of in-plane shear and tension. A multi-step buckling procedure is employed in the Finite Element (FE) model instead of a regular single step analysis in view of obtaining the buckling load under the combined forces. Both the analytical (classical) and FE studies confirm the delayed shear buckling characteristics of thin plate under the combined action of shear and tension. The interaction curves are found to be linear and are found to vary with plate aspect ratio. The interaction curve developed using Rayleigh-Ritz method is found to deviate in an increasing trend from that of validated FE model as plate aspect ratio is increased beyond value of 1. It is found that the observed deviation is due to the insufficient number of terms that is been considered in the assumed deflection function of Rayleigh-Ritz method and a convergence study is suggested as a solution.

• Structural Engineering and Mechanics
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• 제10권6호
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• pp.589-601
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• 2000

A simplified analysis procedure utilizing the strut-tie modeling technique is developed to take a close look into the post-elastic deformation capacity of beam-column connections in ductile reinforced concrete frame structures. Particular emphasis is given to the effect of concrete strength decay and quantity and arrangement of joint shear steel. For this a fan-shaped crack pattern is postulated through the joints. A series of hypothetical rigid nodes are assumed through which struts, ties and boundaries are connected to each other. The equilibrium consideration enables all forces in struts, ties and boundaries to be related through the nodes. The boundary condition surrounding the joints is obtained by the mechanism analysis of the frame structures. In order to avoid a complexity from the indeterminacy of the truss model, it is assumed that all shear steel yielded. It is noted from the previous research that the capacity of struts is limited by the principal tensile strain of the joint panel for which the strain of the transverse diagonal is taken. The post-yield deformation of joint steel is taken to be the only source of the joint shear deformation beyond the elastic range. Both deformations are related by the energy consideration. The analysis is then performed by iteration for a given shear strain. The analysis results indicate that concentrating most of the joint steel near the center of the joint along with higher strength concrete may enhance the post-elastic joint performance.

• 대한조선학회논문집
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• 제45권2호
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• pp.157-167
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• 2008

Six smooth flat tensile specimens and eighteen punch specimens with three different thicknesses were machined from steel of JIS G3131 SPHC. In addition to punch tests, incremental tensile tests were conducted to obtain average true flow stress - logarithmic true strain curves. Through parametric FE simulations for the tensile specimens, material parameters related to GTN model were identified. Using indenters with three kinds of radius, punch tests were carried out to obtain fracture characteristics of punch specimens. Numerical analyses using both fracture models, GTN and $J_2$ plasticity model, gave that the former estimated well the fracture of punch specimen but the latter did not. A new concept for critical size of plate elements was introduced based on minimum relative sharpness between contact structures. Consequently, a new criterion for critical element size was proposed to be less than 20% of minimum relative radius of interacting structures.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2009년도 학술논문요약집
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• pp.187-187
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• 2009

Opening of fractures induced by shear dilation or normal deformation can be a significant source of fracture permeability change in fractured rock, which is important for the performance assessment of geological repositories for spent nuclear fuel. As the repository generates heat and later cools the fluid-carrying ability of the rocks becomes a dynamic variable during the lifespan of the repository. Heating causes expansion of the rock close to the repository and, at the same time, contraction close to the surface. During the cooling phase of the repository, the opposite takes place. Heating and cooling together with the, virgin stress can induce shear dilation of fractures and deformation zones and change the flow field around the repository. The objectives of this work are to examine the contribution of thermal stress to the shear slip of fracture in mid- and far-field around a KBS-3 type of repository and to investigate the effect of evolution of stress on the rock mass permeability. In the first part of this study, zones of fracture shear slip were examined by conducting a three-dimensional, thermo-mechanical analysis of a spent fuel repository model in the size of 2 km $\times$ 2 km $\times$ 800 m. Stress evolutions of importance for fracture shear slip are: (1) comparatively high horizontal compressive thermal stress at the repository level, (2) generation of vertical tensile thermal stress right above the repository, (3) horizontal tensile stress near the surface, which can induce tensile failure, and generation of shear stresses at the comers of the repository. In the second part of the study, fracture data from Forsmark, Sweden is used to establish fracture network models (DFN). Stress paths obtained from the thermo-mechanical analysis were used as boundary conditions in DFN-DEM (Discrete Element Method) analysis of six DFN models at the repository level. Increases of permeability up to a factor of four were observed during thermal loading history and shear dilation of fractures was not recovered after cooling of the repository. An understanding of the stress path and potential areas of slip induced shear dilation and related permeability changes during the lifetime of a repository for spent nuclear fuel is of utmost importance for analysing long-term safety. The result of this study will assist in identifying critical areas around a repository where fracture shear slip is likely to develop. The presentation also includes a brief introduction to the ongoing site investigation on two candidate sites for geological repository in Sweden.