• 터널과지하공간
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• 제32권6호
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• pp.386-396
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• 2022

로드헤더에 미치는 변수의 영향력을 분석하기 위해 픽커터 절삭시험 관련 참고문헌들을 조사하였고, 수록된 데이터들을 수집하였다. 입력 인자는 일축압축강도, 절삭 깊이, 절삭 간격, 받음각, 비틀림각, 출력 인자는 비에너지, 절삭력, 수직력으로 결정했다. 입력 인자와 출력 인자로 분류 후 실험계획법을 작성하였고 분산분석을 이용해 변수들에 대한 기여도를 조사하였다. 그 결과, 절삭력과 비에너지에 가장 큰 영향을 미치는 요인은 일축압축강도와 절삭 간격으로 분석되었다.

• 콘크리트학회논문집
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• 제12권5호
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• pp.121-130
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• 2000

Currently, in evaluating a flexural strength of a concrete member, the effect of specimen depth has not been systematically studied, even though its effect on ultimate strength of a section is very important. For all types of loading conditions, the trend is that the strength of a member tends to decrease when the member depth increases. In this study, the influence of specimen depth on flexural compressive strength of concrete member was examined experimentally. A series of C-shaped specimens subjected to axial compressive force and bending moment were tested using three geometrically similar specimens with different length-to depth ratios (h/c = 1, 2 and 4) which have compressive strength of 55 MPa. The results indicate that the flexural compressive strength decreased as the specimen depth increased. A model equation was derived based on regression analyses of the experimental data. Also, the results show that ultimate strain decreases as the specimen depth increases. Finally, a general model equation for the depth effect is proposed.

• 한국강구조학회 논문집
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• 제9권2호통권31호
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• pp.171-179
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• 1997

고장력 볼트 이음부에서의 힘의 전달은 부재간의 압축력 및 볼트축력에 의하여 외력과 균형을 이룸으로서 형성되어지며, 부재간의 압축력, 도입된 축력의 변화 및 미끄러짐하중 등은 볼트 체결부 및 볼트의 유효강성에 지배된다. 이때 유효강성은 일반적으로 접합부의 유효단면적과 탄성계수의 곱으로 나타내어지지만 접합부재의 유효단면적이 어느 정도가 되는지는 판단하기가 쉽지가 않다. 이를 위해서 종래에는 이음부의 탄성변형에 관계하는 유효단면적을 등가중공원통형으로 가정하여 이에 대한 여러 가지 검토가 이루어졌다. 그러나 이러한 제안식들은 설계상의 목적과 복잡한 계산을 피하기 위하여 매우 단순화시킨 것으로 어느 식이 타당한 지는 단정하기가 어려우며 이에 대한 상세한 해석적인 검토 및 실험적인 검증이 요구된다. 따라서, 본 연구에서는 볼트 축력에 의한 접합부재의 유효단면적 산정과 이에 대한 검증을 위하여 고장력 볼트 이음 시험편에 대해 피로시험을 실시하고 반복하중 재하 후의 마찰면의 형상을 관찰하여 유효마찰 영역을 측정하였으며, 유한 요소법에 의해 수치 해석을 실시하여 내부 압축응력의 분포형상을 밝히고 접촉면상에 발생하는 응력 분포영역을 근사화하므로서 마찰면의 형상과 내부 압축응력의 분포영역과의 관계 그리고 유효단면적의 산정 방법을 고찰하였다.

• 대한치과교정학회지
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• 제26권6호
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• pp.691-703
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• 1996

Three-dimensional finite element model was made from adult skull to find desirable direction of retraction force to treat skeletal class II malocclusion. The retraction force of 400g was applied to the first molar. The direction of the force application was $23^{\circ}$ downward, parallel, $23^{\circ}$ upward and $45^{\circ}$ upward to the occlusal plane. The stress distribution and the displacement within the maxilla were analyzed by three-dimensional finite element method. The findings obtained were as follows: 1. Maxillary first molar was displaced posteriorly and inferiorly in $23^{\circ}$ downward, parallel, $23^{\circ}$ upward retraction but it was displaced posteriorly and superiorly in $45^{\circ}$ upward retraction. 2. ANS, A point and prosthion were moved posteriorly and inferiorly and pterygomaxillary fissure was moved posteriorly and superiorly. Clockwise rotation of maxilla occurred when retraction force was applied. 3. The degree of clockwise rotation of maxilla was greatest when the force was applied $23^{\circ}$ upward to the occlusal plane and was least when the force was applied $23^{\circ}$ downward to the occlusal plane. 4. Large tensile stress appeared in maxillary first molar and alveolar bone and the infraorbital region of maxilla when the force was applied $23^{\circ}$ downward to the occlusal plane. Tensile stress was smaller as the direction of force move upward. 5. Large compressive stress was appeared in maxillary first molar and infraorbital region in $45^{\circ}$ upward case and large compressive stress occurred in the posterior part of maxilla as the retraction force was upward.

• 한국산업보건학회지
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• 제16권2호
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• pp.161-171
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• 2006

The objectives of this study were to ergonomically evaluate varying tasks performed in a general hospital and to propose their improving measures based on the evaluation results. The tasks found in the hospital were largely classified into two groups of manual materials handling and awkward posture related tasks. Ergonomic tools of NLE, 3-D SSPP and RULA were used for evaluating workload of the tasks. The major findings are: 1) L5/S1 compressive force of patient transferring by one person exceeded the maximum permissible limit(6,400N) by NIOSH. The L5/S1 compressive forces for most of the patient transferring tasks by 2-4 persons were larger than the action limit (3,400N), and the tasks by five persons were analyzed to be safe in the view of L5/S1 compressive force; 2) patient repositioning tasks by 2-3 persons were hazardous on the basis of L5/S1 compressive force, while most of the tasks by 4-5 persons were safe; 3) many tasks performed in wards were found to be stressful, most of which resulted from improper heights of their working tables or working points. Of varying tasks in general hospitals, patient transferring was the most stressful. Based on the results of this study and high prevalence of musculoskeletal disorders from other studies, it is recommended that the ergonomics program be introduced and enforced for doing improving activities systematically

• 한국구조물진단유지관리공학회 논문집
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• 제12권4호
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• pp.71-78
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• 2008

철도교량의 경우, 열차하중에 의한 영향으로 교량 단부에서 상향력이 발생하였으며, 이 상향력은 체결장치에 압축력과 인장력을 유발시켰다. 현재까지 이에 대한 안전성을 검토하기 위해 체결장치를 1방향의 스프링 요소로 모사하여 구조해석을 수행해 왔다. 이러한 경우에 스프링 요소의 강성은 압축력을 재하한 실험적 연구에 의하여 산정되었다. 따라서, 상향력은 체결장치에 압축력뿐만 아니라 인장력도 유발시키기 때문에 합리적이고 정확한 구조해석을 수행하기 위해서는 인장력을 재하한 실험적 연구로부터 산정된 병진방향 강성 그리고 회전방향 강성을 함께 고려해야 한다. 본 연구에서는 6가지 실험체에 대하여 탄성과 비탄성 실험을 수행하여 레일 연직방향 병진강성과 레일 강축에 대한 회전강성을 검토하였고, 체결장치의 구조적인 거동을 분석하였다.

• Geomechanics and Engineering
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• 제34권5호
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• pp.577-595
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• 2023

A dynamic triaxial discrete element numerical model of lightweight soil was established using the discrete element method to study the microscopic mechanism of expanded polystyrene (EPS) particles in the soil under cyclic loading. The microscopic parameters of the discrete element model of the lightweight soil were calibrated depending on the dynamic triaxial test hysteresis curves. Based on the calibration results, the effects of the EPS particles volume ratio and amplitude on the contact force, displacement field, and velocity field of the lightweight soil under different accumulated strains were studied. The results showed that the hysteresis curves of lightweight soil exhibit nonlinearity, hysteresis, and strain accumulation. The strain accumulated in remolded soil is mainly tensile strain, and that in lightweight soil is mainly compressive strain. As the volume ratio of EPS particles increased, the contact force first increased and then decreased, and the displacement and velocity of the particles increased accordingly. With an increase in amplitude, the dynamic stress of the particle system increased, and the accumulation rate of the dynamic strain of the samples also increased. At 5% compressive strain, the contact force of the particles changed significantly and the number of particles deflected in the direction of velocity also increased considerably. These results indicated that the cemented structure of the lightweight soil began to fail at a compressive strain of 5%. Thus, a compressive strain of 5% is more reasonable than the dynamic strength failure standard of lightweight soil.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.115-120
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• 2000

Currently, in evaluating a flexural strength of a concrete member, the effect of specimen depth has not been systematically studied, even though its effect on ultimate strength of a section is very important. For all types of loading conditions, the trend is that the strength of a member tends to decrease when the member depth increases. In this study, the influence of specimen depth on flexural compressive strength of concrete member was examined experimentally. A series of C-shaped specimens subjected to axial compressive force and bending moment were tested using three geometrically similar specimens with different length-to-depth ratios(h/c=1, 2 and 4) which have compressive strength of 55MPa. The results indicate that the flexural compressive strength decreased as the specimen depth increased. A model equation was derived based on regression analyses of the experimental data. Also the results show that ultimate strain decreases as the specimen depth increases. Finally, a general model equation for the depth effect is proposed.

• 한국생산제조학회지
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• 제7권5호
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• pp.120-126
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• 1998

Second step shot peening was applied on both smooth specimen and U-notch specimen in order to investigate the stress distribution and the improvement in fatigue strength. Various experiments and measurements such as rotary bending fatigue test and the measurement of compressive residual stress were performed. The results showed that the fatigue strength of second step shot peened specimens increased by 34 percent compared to that of unpeened ones. Compressive residual stress also considerably increased, which resulted in the increase of fatigue strength. finite element analysis showed that shot peening is effective in decreasing the bending stress by external force. The effectiveness of shot peening in reducing the compressive residual stress was anticipated by the superposition of the concentrated stress and the compressive residual stress.

• 대한치과교정학회지
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• 제39권4호
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• pp.248-256
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• 2009

이 연구의 목적은 배양된 사람 치주인대 세포에서 파골세포의 형성에 관련된 물질을 합성, 분비할 수 있는지를 알아보고 압박력이 M-CSF, IL-$1{\beta}$, RANKL 및 OPG mRNA의 발현에 미치는 영향을 알아보고자 하였다. 교정치료를 목적으로 발치된 소구치에서 얻은 치주인대세포를 배양한 후 다양한 크기(0.5, 1.0, 2.0, 3.0, $4.0\;g/cm^2$)의 기계적 자극을 다양한 기간(0.5, 1.5, 6, 24, 48 hours) 동안 적용하고, M-CSF, IL-$1{\beta}$, RANKL, OPG mRNA 발현양의 변화를 검사하였다. 각각의 실험군에서 얻어진 mRNA에 대해 역전사 중합효소 연쇄반응검사를 시행하였다. 검사 결과 압박력은 사람 치주인대 세포에서 M-CSF mRNA를 발현시켰으며 M-CSF, IL-$1{\beta}$, RANKL mRNA의 발현양은 자극의 크기와 기간에 따라 증가하였다. 그러나 압박력은 사람 치주인대 세포에서 OPG mRNA의 발현양에 영향을 미치지 않는 것으로 나타났다. 이상의 결과는 기계적 자극이 치주인대 세포에서 M-CSF, IL-$1{\beta}$, RANKL mRNA의 발현양을 조절함으로 파골세포의 분화에 영향을 미칠 수 있음을 시사한다.