• Structural Engineering and Mechanics
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• 제70권3호
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• pp.279-287
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• 2019

This paper intends to introduce a near-tip grid refinement and to explore its usefulness in the crack analysis by the natural element method (NEM). As a sort of local h-refinement in FEM, a NEM grid is locally refined around the crack tip showing the high stress singularity. This local grid refinement is completed in two steps in which grid points are added and Delaunay triangles sharing the crack tip node are divided. A plane-state plate with symmetric edge cracks is simulated to validate the proposed local grid refinement and to examine its usefulness in the crack analysis. The crack analysis is also simulated using a uniform NEM grid for the sake of comparison. The near-tip stress distributions and SIFs that are obtained using a near-tip refined NEM grid are compared with the exact values and those obtained using uniform NEM grid. The convergence rates of global relative error to the total number of grid points between the refined and non-refined NEM grids are also compared.

• 비파괴검사학회지
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• 제9권1호
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• pp.48-55
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• 1989

It is desirable to develop the effective NDT techniques to evaluate the strength of composite structures. In this study several of acoustic NDT techniques were applied to investigate useful parameters for evaluating the filament wound GFRP structures and following results were obtained. 1. Propagation velocity of stress wave to axial direction in the filament wound GFRP pipe depends on the effective modulus along the propagation direction and source location was parcticable from the a measured velocities. 2. By the application of acoustic emission techniques to GFRP pipe during hydraulic test, it was proven to be possible to detect the damage initiating pressure which could be evaluated nondestructively through the measuring of stress wave energy factor(SWEF). 3. The final failure pressure of GFRP was greatly influenced in the presence of pass through defects, and void-like defects were more dangerous than the laminar type defects.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.28-32
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• 1995

This effective way for repairing a fatigue crack is making indetations around fatigue crack tip. In this paper, we performed fatigue test to investigate the optimal position of the indentations, and observed crack opening behavior at the same time. The indentation positions of specimens were on the crack tip, front and back of the crack tip. The results of the experiment showed taht it was veryeffective way to increase fatigue life that making indentations on the crack tip, and it was the optimal position that making indentations on the crack tip.

• 지구물리
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• 제6권2호
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• pp.107-119
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• 2003

The behavior of pore pressure and effective stress in a highly saturated sand bed under variations in the water pressure in its surface were investigated to determine the mechanism of the collapse of hydraulic structures during flooding or when attacked by storm waves. The vertical, one-dimensional model was used as a basic model to clarify the effect of water pressure variation on only to the vertical direction. The theoretical results show that a sand bed under variations of water pressure is weakened by an increase in excess pore pressure and that under certain conditions the sand bed will liquefy. Although many factors related to water pressure variation and property of the material determine this phenomenon, the mist important factor seems to be the small amount of air present in the sand bed. The theoretical results reported are verified by experiments.

• Steel and Composite Structures
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• 제47권3호
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• pp.383-393
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• 2023

Conventional reinforced concrete design codes assume ideal strain evolution in semi-deep beams with externally bonded fiber-reinforced polymer (EB-FRP) web strips. However, there is a strain interaction between internal stirrups and web strips, leading to a notable difference between code-based and experimental shear strengths. Current study provides an experiment-verified detailed numerical framework to assess the potential strain interaction under quasi-static monotonic load. Based on the observations, steel stirrups are effective only for low EB-FRP amounts and the over-strengthening of semi-deep beams prevents the stirrups from yielding, reducing its shear strength contribution. A notable difference is detected between the code-based and the study-based EB-FRP strain values, which is a function of the normalized FRP stress parameter. Semi-analytical relations are proposed to estimate the effective strain and stress of the components considering the potential strain interaction. For the sake of simplification, a linearized correction factor is proposed for the EB-FRP web strip strain, assuming its restraining effect as constant for all steel stirrup amounts.

• 대한인간공학회지
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• 제26권2호
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• pp.45-59
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• 2007

The operating tasks of overhead crane have caused undue stress to the operators from physical, mental, and environmental workload. Existing workload assessment models for musculoskeletal disorders such as OWAS, RULA, and QEC have limited applicability to the crane operating tasks because they focus mainly on physical factors and do not consider the relative importance of each factor. The present study was to develop a workload assessment model customized to overhead crane operation, following a systematic process: (1) analyzing task characteristics, (2) selecting workload factors, (3) developing assessment methods, (4) establishing action levels, and (5) computerizing the assessment model. Based on literature review, worksite survey, and focus group interview, 4 physical factors (awkward posture, static posture, repetitive motion, and excessive force), 6 mental factors (visual demand, auditory demand, task complexity and difficulty, time urgency, work schedule related stress, and safety related stress), and 4 environmental factors (noise, vibration, dust, and temperature) were selected and their rating scales and relative weights were determined. Then, based on the workload assessment results of 8 overhead cranes operated at different workplaces, the action levels of each factor category were established. Finally, the crane operation assessment model was computerized for effective analysis and report preparation. The present approach is applicable to develop a customized workload assessment model for an operating task under consideration.

• 한국콘텐츠학회논문지
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• 제12권6호
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• pp.380-389
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• 2012

본 연구는 국내 작업치료사의 직무스트레스에 영향을 미치는 요인들에 대한 여러 선행 연구들의 결과에 대해 체계적 고찰 및 메타분석을 실시하여 스트레스 관련 요인들의 차이를 비교해 봄으로써 향후 작업치료사의 직무스트레스 예방 및 완화, 효과적인 대처 방법 마련에 대한 정보를 제공해 작업치료의 질 향상과 작업치료 인력관련 정책을 수립하는데 기초자료를 제시하고자 하였다. 선정기준에 적합한 총 8건의 논문이 선정되었고, 이중 메타분석을 위해 크기의 변환이 가능한 통계치를 밝히고 있는 연구 5건을 대상으로 상관계수를 이용한 메타분석을 실시해 전체 상관계수 값과 요인별 상관계수 값을 구하였으며 대상 논문들의 동질성 검정과 출판편견 검정을 실시하였다. 그 결과 작업치료사의 직무스트레스 요인에 대한 전체 효과크기에 대한 95%의 신뢰구간은 .27에서 .34로 이 값은 통계적으로 유의하였다. 직무스트레스 요인들 중 조직관련 요인이 가장 높은 상관관계를 보였고, 그 다음으로 조직외관련 요인, 물리적환경 요인, 직무관련 요인, 개인관련 요인 순으로 상관관계를 나타내었다. 또한 출판편견을 배제할 수 있어 본 연구 결과는 신뢰할 수 있음을 뒷받침 해주고 있다. 이 연구는 작업치료사의 직무스트레스 예방 및 완화, 효과적인 대처 방법 마련을 위해 참고할 수 있는 자료를 제공하였다는데 의의가 있다.

• 한국공간구조학회논문집
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• 제13권4호
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• pp.67-74
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• 2013

The Age-adjusted effective Modulus Method(AEMM) is one of the methods adopted for the construction stage analysis of concrete structures. The AEMM uses the aging factor to consider the effects of the varying concrete stress. In the aspects of computation time and the accuracy of the results, the AEMM is considered as one of most appropriate methods for construction stage analysis of tall building structures. Previous researches proposed appropriate values of the aging factor in the forms of graphs or using very simple equations. In this paper, an equation for estimating the aging factor as a function of rebar ratio in the section, compressive strength of concrete, notional member dimension, and age of concrete at the load application. The validity of aging factor proposed in this paper were examined by the comparison with the results of step-by step method.

• Computers and Concrete
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• 제7권5호
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• pp.437-453
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• 2010

CFRP has been widely used for strengthening reinforced concrete members in last decade. The strain transfer mechanism from concrete face to CFRP is a key factor for rigidity, ductility, energy dissipation and failure modes of concrete members. For these reasons, determination of the effective CFRP bonding length is the most crucial step to achieve effective and economical strengthening. In this paper, generalizations are made on effective bonding length by increasing the amount of test data. For this purpose, ANSYS software is employed, and an experimentally verified nonlinear finite element model is prepared. Special contact elements are utilized along the concrete-CFRP strip interface for investigating stress distribution, load-displacement behavior, and effective bonding length. Then results are compared with the experimental results. The finite element model found consistent results with the experimental findings.

• 한국직업건강간호학회지
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• 제22권3호
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• pp.257-265
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• 2013

Purpose: This study aimed to investigate the job stress level of call center workers and figure out its relation with cognitive emotion regulation strategies as a cognitive coping strategy. Methods: Data collection was conducted on 985 call center workers, working for K companies in Korea. ANOVA, t-test, Scheffe's test and multiple regression have been conducted for the data analysis using SAS 9.0 software. Results: The total job stress score of subjects ranges $Q_{25{\sim}49}$ (the lower 50%) whereas the score of job demand and job control ranges $Q_{50{\sim}74}$ (the upper 50%), and its sectional job stress level is high. Since job stress is the major factor affecting cognitive emotion regulation strategies, it is shown that when the job stress score gets higher, the score of positive cognitive emotion regulation strategies gets decreased but the score of negative cognitive emotion regulation strategies, increased. Conclusion: Based on the results of this study, it is necessary to develop and apply an effective stress easing method for call center workers which reduces negative cognitive emotion regulation strategies and increases positive ones.