• 한국전산구조공학회논문집
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• 제15권3호
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• pp.523-534
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• 2002

본 논문에서는 축방향 압축하중을 받는 다퐁간분리된 적층 보-기둥의 자유진동과 좌팔에 대한 해석을 수행하였다. 다층간분리된 적층 보-기둥의 고유진동수와 탄성 좌굴 하중에 대한 층간분리의 영향을 조사하기 위해 층간분리의 양단에서 기울기와 곡률이 일정하다는 가정을 적용하여 일반적인 운동학적 연속 조건을 유도하였다. 전체 다층간분리된 보-기둥을 부분으로 분할하고, 연속조건에 따른 반복관계를 각 하부 보-기둥에 부과함으로써 다층간분리된 보-기둥의 특성방정식을 구하였다. 축방향 증분 압축 하중에 따른 다층간분리된 보-기둥의 고유진동수와 탄성 좌굴 하중을 구하였으며 이는 손상되지 않은 적층 보-기둥의 최대 탄성 좌굴 하중에 한정된다 연구를 통하여 층간분리의 크기, 위치, 수가 고유진동수와 특히 탄성 좌굴 하중에 큰 영향을 미치는 것을 알 수 있었다.

• Radiation Oncology Journal
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• 제16권1호
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• pp.81-86
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• 1998

목적 : Broad-beam Simulator-CT 개발을 위한 예비연구로서 통상의 모의 치료 영상에서 축상면, 시상면, 관상면 영상을 구현하려 하였다. 대상 및 방법 : 120kVp, 2mAs 동일 조건에서 갠트리 각도를 $4^{\circ}$ 간격으로 90장의 필름을 얻어 입체적인 Filtered back-projection을 시도하였다 외곽선을 찾아 제거하였고, 산란선 성분을 Deconvolution 방법으로 제거하여 좋은 영상을 얻도록 하였다. 결과 : 이 방법으로 축상면, 시상면, 관상면 영상을 얻었으며 각 방향에 대해 동일한 분해능을 갖았다. 그러나 영상의 질은 대단히 나빴다. 결론 : Broad-beam으로 된 CT 영상을 구현할 수 있었다. 이를 위하여 산란선 성분의 Deconvolution이 필요하였으며, 입체적인 back-projection을 실시하였으므로 축상, 시상, 관상 모든 방향에 대해 동일한 분해능을 갖고 있어서 DRR 등 Simulator-CT에 응용할 수 있음을 알 수 있었다. 그러나 실용적인 임상응용을 위해서는 영상의 질 개선이 필요하였다.

• 대한치과교정학회지
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• 제43권5호
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• pp.209-217
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• 2013

Objective: This study investigated whether temporomandibular joint (TMJ) condyle-fossa relationships are bilaterally symmetric in class III malocclusion patients with and without asymmetry and compared to those with normal occlusion. The hypothesis was a difference in condyle-fossa relationships exists in asymmetric patients. Methods: Group 1 comprised 40 Korean normal occlusion subjects. Groups 2 and 3 comprised patients diagnosed with skeletal class III malocclusion, who were grouped according to the presence of mandibular asymmetry: Group 2 included symmetric mandibles, while group 3 included asymmetric mandibles. Pretreatment three-dimensional cone-beam computed tomography (3D CBCT) images were obtained. Right- and left-sided TMJ spaces in groups 1 and 2 or deviated and non-deviated sides in group 3 were evaluated, and the axial condylar angle was compared. Results: The TMJ spaces demonstrated no significant bilateral differences in any group. Only group 3 had slightly narrower superior spaces (p < 0.001). The axial condylar angles between group 1 and 2 were not significant. However, group 3 showed a statistically significant bilateral difference (p < 0.001); toward the deviated side, the axial condylar angle was steeper. Conclusions: Even in the asymmetric group, the TMJ spaces were similar between deviated and non-deviated sides, indicating a bilateral condyle-fossa relationship in patients with asymmetry that may be as symmetrical as that in patients with symmetry. However, the axial condylar angle had bilateral differences only in asymmetric groups. The mean TMJ space value and the bilateral difference may be used for evaluating condyle-fossa relationships with CBCT.

• 콘크리트학회논문집
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• 제13권2호
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• pp.153-160
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• 2001

본 연구에서는 콘크리트 부재에서의 축압축강도에 대한 크기효과를 검토하였다. 이를 위하여 두 가지 대표적인 압축파괴모드 중의 하나인 모드 I 파괴에 대한 실험적 연구를 이중 캔틸레버 보를 이용하여 수행하였다. 각 캔틸레버의 축에 대한 작용하중의 편심거리와 초기 균열길이를 변화시킴에 의하여 콘크리트의 축압축강도에도 크기효과가 존재하는 지의 여부를 확인하였고, 최소자승법을 이용하여 수정된 크기효과법칙의 새로운 실험상수들을 제시하였다. 연구결과로부터 초기 균열이 있는 콘크리트 부재의 축압축강도에도 크기효과가 존재함을 확인하였다. 하중의 편심거리에 있어서는 균열선단에서의 인장과 압축응력의 영향이 매우 중요하며 이 경우에 뚜렷한 크기효과가 나타났다. 즉 균열선단에서 인장응력의 영향이 증가하면 콘크리트의 크기효과는 증가한다. 그러나 초기 균열길이의 경우, 축압축강도의 크기효과에 미치는 영향은 존재하지만 균열길이에 따른 차이는 뚜렷하지 않았는데 이는 고강도 콘크리트 부재의 경우 부재의 세장비 차에도 불구하고 파괴진행영역의 크기가 서로 비슷한데 그 원인이 있는 것으로 판단된다.

• Smart Structures and Systems
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• 제19권6호
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• pp.625-631
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• 2017

In the fields of civil engineering and seismology, it is essential to detect and tracking the vibrations, and the fiber Bragg gratings (FBGs) are typically used as sensors to measure vibrations. Where, one of the most popular and detailed approaches to use FBGs as vibration sensors involves the use of cantilever beam designs, which adds a mass to measure low and moderate frequencies (from 20 Hz up to 1 kHz) with high sensitivities (greater than 10 pm/g). The design consists of a bending strain in the cantilever that is simultaneously transferred to the FBG, resulting in a shift in the wavelength that is proportional to the strain experienced by the cantilever. In this work, we present the experimental results of a vibration sensor design using a cantilever beam to generate an axial uniform strain in the FBG in-line with the vertical axis, which modifies the cantilever's natural frequency that allows the sensor to have a wide frequency broadband without losing sensitivity. This sensor achieved a sensitivity of about 339 pm/g and a natural frequency of 227.3 Hz. The presented design compared with the traditional cantilever beam-based FBG vibration sensors, has the advantages of a simple design for detection on vibration-sensitive structures and its physical parameters can be easily modified in order to satisfy the requirements of the desired vibration measurements.

• Structural Engineering and Mechanics
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• 제58권5호
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• pp.847-868
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• 2016

In this study, the free vibration analysis of axially moving beams is investigated according to Reddy-Bickford beam theory (RBT) by using dynamic stiffness method (DSM) and differential transform method (DTM). First of all, the governing differential equations of motion in free vibration are derived by using Hamilton's principle. The nondimensionalised multiplication factors for axial speed and axial tensile force are used to investigate their effects on natural frequencies. The natural frequencies are calculated by solving differential equations using analytical method (ANM). After the ANM solution, the governing equations of motion of axially moving Reddy-Bickford beams are solved by using DTM which is based on Finite Taylor Series. Besides DTM, DSM is used to obtain natural frequencies of moving Reddy-Bickford beams. DSM solution is performed via Wittrick-Williams algorithm. For different boundary conditions, the first three natural frequencies that calculated by using DTM and DSM are tabulated in tables and are compared with the results of ANM where a very good proximity is observed. The first three mode shapes and normalised bending moment diagrams are presented in figures.

• Structural Engineering and Mechanics
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• 제38권5호
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• pp.573-592
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• 2011

Comprehensive and accurate analysis of a finite foundation beam is a challenging engineering problem and an important subject in foundation design. One of the limitation of the traditional Winkler elastic foundation model is that the model neglects the effect of the interface resistance between the beam and the underneath foundation soil. By taking the beam-soil interface resistance into account, a deformation governing differential equation for a finite beam resting on the Winkler elastic foundation is developed. The coupling effect between vertical and horizontal displacements is also considered in the presented method. Using Galerkin method, semi-analytical solutions for vertical and horizontal displacements, axial force, shear force and bending moment of the beam under symmetric loads are presented. The influences of the interface resistance on the behavior of foundation beam are also investigated.

• Geomechanics and Engineering
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• 제11권1호
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• pp.95-116
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• 2016

A novel higher order shear-deformable beam model, which provides linear variation of transversal normal strain and quadratic variation of shearing strain, is proposed to describe the beam resting on foundation. Then, the traditional two-parameter Pasternak foundation model is modified to capture the effects of the axial deformation of beam. The Masing's friction law is incorporated to deal with nonlinear interaction between the foundation and the beam bottom, and the nonlinear properties of the beam material are also considered. To solve the mathematical problem, a displacement-based finite element is formulated, and the reliability of the proposed model is verified. Finally, numerical examples are presented to study the effects of the interfacial friction between the beam and foundation, and the mechanical behavior due to the tensionless characteristics of the foundation is also examined. Numerical results indicate that the effects of tensionless characteristics of foundation and the interfacial friction have significant influences on the mechanical behavior of the beam-foundation system.

• 한국강구조학회 논문집
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• 제9권4호통권33호
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• pp.557-578
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• 1997

이 연구의 목적은 매우 큰 지진하에 휨 모멘트에 의해서만 항복하는 부재와 휨 모멘트와 축 방향력에 의하여 항복하는 부재를 모델 할 수 있는 보-기둥 요소를 개발하는데 있다. 이 요소는 직렬 힌지 모델 (one-component series hinge model)로 간주 될 수 있으며, 축 방향 강성도 변화와 축 방향 소성 변형을 고려 할 수 있고 또한 단조, 주기, 임의 하중 등을 적절히 모델 할 수 있는 경화 법칙 (hardening rules)을 고려한다. 일반적으로 이 요소는 실험 결과 및 화이버 모델 (fiber model)에 비교하여 볼 때 기존의 이직선 힌지 모델 (bilinear hinge model)보다 우수한 거동을 보였고 모멘트 저항 뼈대 구조물의 강 부재의 보-기둥 거동을 적절하게 모델 할 수 있었다. 개발된 보-기둥 요소는 지진 하중하에서 구조물의 전체적인 거동과 설계에 필요한 국부 변형량을 기존의 이직선 힌지 모델 보다 매우 정확하게 예측 할 수 있다.

• Computers and Concrete
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• 제31권6호
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• pp.537-543
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• 2023

To study the seismic behavior of recycled aggregate concrete filled circular steel tube (RACFCST) frames, the seismic behavior experiment of RACFCST frame was carried out to measure the hysteresis curve, skeleton curve and other seismic behavior indexes. Moreover, based on the experimental study, a feasible numerical analysis model was established to analyze the finite element parameters of 8 RACFCST frame specimens, and the influence of different variation parameters on the seismic behavior index for RACFCST frame was revealed. The results showed that the skeleton curve of specimens under different axial compression ratios were divided into three stages: elastic stage, elastic-plastic stage and descending stage, and the descending stage was relatively stable, indicating that the specimen had stronger deformation capacity in the descending stage. With the increase of axial compression ratio, the peak bearing capacity of all specimens reduced gradually, and the reduction was less than 5%. With the decrease of beam-column linear stiffness ratio, the peak bearing capacity decreased gradually. With the decrease of yield bending moment ratio of beam-column, the peak bearing capacity decreased gradually, and the decreasing rate of peak bearing capacity gradually accelerated. In addition, compared with the axial compression ratio, the beam-column linear stiffness ratio and the yield bending moment ratio of beam-column had a more significant influence on the peak bearing capacity of RACFCST frame.