• 한국직업건강간호학회지
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• 제15권2호
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• pp.115-125
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• 2006

Purpose: This study analyzed the amount of stress and the different effects according to the working times(hours) of a week in two groups: more than 40 hours a week and less than 40 hours a week. Method: The study was conducted from November 1st 2005 to December 15th 2005. The purpose of the study has already been explained in the experiment objectives. 20 copies of evaluation forms were sent by mail to 50 different health sections of participating work sites. A total of 1,000 copies were sent out and 870 were sent back. Within the forms, sent back 120 copies had insufficient data, so 750 copies of evaluation forms were analyzed. Result: Working stress for under 40 hours of working time showed a total of 46.10 points and 47.18 for over 40 hours of working time. For over 40 hours, job demand and occupational climate was high and under 40 hours showed a high rate of job control. For under 40 hours of working time, the factors that caused stress were female, irregular diet habit, age of 30's, nonmanufacturing, and single. For over 40 hours of working time, the factors that causes stress were age of over 40, when the number of employees is 500~999, high rate of fatigue, when the position of the employee is higher then section chief, and when the work amount is high. Conclusion: The stress rate showed significantly higher in over 40 hours of working time. Therefore, adequate working hour distribution and health promotion programs are needed. The factors that cause stress in both under and over 40 hours of working time differed. Therefore, a distinguished program to control work stress for additional working time is needed.

• 대한기계학회논문집A
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• 제30권3호
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• pp.269-278
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• 2006

This paper proposes slip line fields for bending of unequally notched specimens in plane strain that have a sharp crack in one side and a sharp V-notch in the other side. Depending on the back angle, two slip line fields are proposed, from which the limit moment and crack tip stress fields are obtained as a function of the back angle. Excellent agreement between slip line field solutions with those from detailed finite element limit analysis based on non-hardening plasticity provides confidence in the proposed slip line fields. One interesting point is that, for the unequally notched specimen, the difference between the crack tip triaxial stress for tension and that for bending increases significantly with increasing the back angle. This suggests that such a specimen could be potentially useful to investigate the crack tip constraint effect on fracture toughness of materials. In this respect, the possibility of designing a new toughness testing specimen with varying crack tip constraint is discussed.

• Structural Engineering and Mechanics
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• 제27권5호
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• pp.575-588
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• 2007

In this paper, two algorithms are presented for the optimum design of geometrically nonlinear steel space frames using tabu search. The first algorithm utilizes the features of short-term memory (tabu list) facility and aspiration criteria and the other has long-term memory (back-tracking) facility in addition to the aforementioned features. The design algorithms obtain minimum weight frames by selecting suitable sections from a standard set of steel sections such as American Institute of Steel Construction (AISC) wide-flange (W) shapes. Stress constraints of AISC Allowable stress design (ASD) specification, maximum drift (lateral displacement) and interstorey drift constraints were imposed on the frames. The algorithms were applied to the optimum design of three space frame structures. The designs obtained using the two algorithms were compared to each other. The comparisons showed that the second algorithm resulted in lighter frames.

• 한국자동차공학회논문집
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• 제22권2호
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• pp.141-147
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• 2014

This study aims to investigate the influence of bevel angles on the fatigue life of V-groove butt-welded joints with back-plates made by SM490A steel material, generally used for excavators, because changes in the geometry, material and surface properties of welded regions affect the fatigue life of welded structures. Butt type test specimens were prepared by the $CO_2$ welding of rolled steel plates (SM50A steel) with a thickness of 13.5 mm at a welding speed of 30 cm/min and these Butt type test specimens had two different groove angles, which are $40^{\circ}$ (A type) and $30^{\circ}$ (B type). In order to investigate differences in fatigue life between two types, 4-point bending fatigue tests were conducted with a stress ratio of R=0.1 under the cyclic loading environment at a frequency of 5 Hz at room temperature. The fatigue life of A type specimens was approximately 7% higher than that of B type specimens. The stress concentration factors calculated by finite element analysis were 2.16 for A type and 2.25 for B type, whose difference was caused by the influence of the back-plates of butt-welded structures. The current results could provide important guidelines to determine the V-groove angle of butt-welded joints with a satisfactory fatigue life, although under severe operating conditions.

• 산업경영시스템학회지
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• 제37권4호
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• pp.72-81
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• 2014

Even though two-hands lifting/lowering activity of manual materials handling tasks are prevalent at the industrial site, many manual materials handling tasks which require the worker to perform one-hand lifting/lowering are also very common at the industrial site, forestry, farming, and daily life. The objective of this study was to compare one-hand lowering activity to lifting activity in terms of biomechanical stress for the range of lowering heights from knuckle height to 10cm above floor level with two workload 7.5kg and 15.0kg. Eight male subjects with LMM were asked to perform lifting/lowering tasks using both a one-handed (left-hand and right-hand) as well as a two-handed technique. Spinal loading was estimated through an EMG-assisted free-dynamic biomechanical model. The biomechanical stress of one-hand lowering activity was shown to be 43% lower than that of one-hand lifting activity. It was claimed that the biomechanical stress for one-hand lifting/lowering activity is almost twice (194%) of the one for two-hands lifting/lowering activity. It was also found that biomechanical stress by one-hand lowering/lifting activity with the half workload of two-hands lowering/lifting activity was greater than that of the two-hands lowering/lifting activity. Therefore, it might be a risk to consider the RWL of one-hand lowering/lifting activity to simply be a half of the RWL of two-hands lowering/lifting activity recommended by NIOSH.

• 대한인간공학회지
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• 제32권5호
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• pp.413-420
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• 2013

Objective: The objective of this study was to compare one-hand and two-hands lowering activity in terms of biomechanical stress for the range of lowering heights from knuckle height to 10cm above floor level. Background: Even though two-hands lifting/lowering activity of manual materials handling tasks are prevalent at the industrial site, many manual materials handling tasks which require the worker to perform one-hand lifting/lowering are also very common at the industrial site and forestry and farming. Method: Eight male subjects were asked to perform lowering tasks using both a one-handed as well as a two-handed lowering technique. Trunk muscle electromyographic activity was recorded while the subjects performed the lowering tasks. This information was used as input to an EMG-assisted free-dynamic biomechanical model that predicted spinal loading in three dimensions. Results: It was shown that for the left-hand lowering tasks, the values of moment, lateral shear force, A-P shear force, and compressive force were increased by the average 6%, as the workload was increased twice from 7.5kg to 15kg. For the right-hand lowering task, these were increased by the average 17%. For the two-hands lowering tasks, these were increased by the average 14%. Conclusion: Even though the effect of workload on the biomechanical stress for both one-hand and two-hands lowering tasks is not so significant for the workload less than 15kg, it can be claimed that the biomechanical stress for one-hand lowering is greater than for two-hands lowering tasks. Therefore, it can be concluded that asymmetrical lowering posture would give greater influence on the biomechanical stress than the workload effect for one-hand lowering activity. Application: The result of this study may be used to provide guidelines of recommended safe weights for tasks involved in one-hand lowering activity.

• 터널과지하공간
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• 제9권4호
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• pp.296-305
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• 1999

많은 터널 현장에서 계측을 수행하고 있지만, 일반적인 역해석 방법으로 이 계측자료를 통해 라이닝에 작용하는 변형율과 응력 등의 역학량을 추정하기는 어렵다. 그 이유는 현장에서 계측이 가능한 적은 변위수로부터 라이닝의 응력상태를 추정할 수 없기 때문이다. 계측의 시간과 비용을 고려해 볼 때, 계측자료를 이용할 수 있는 기법의 개발은 시급한 연구과제라 할 수 있다. 본 연구에서는 터널계측에서 계측 가능한 소수의 변위로 전테 라이닝의 변위와 응력 등의 역학량을 계산할 수 있는 역해석 모델을 개발하였다. 역해석 방법으로서 복공 외면에 작용하는 외력의 자승이 최소화될 때 해를 구하는 방법을 사용하였다. 라이닝 외면에 작용하는 하중을 가정하여 유한요소법으로 변위와 응력을 계산하고, 여기서 얻은 몇개의 변위를 계측 변위로 가정하여 역해석 모델에 입력함으로써 절점 변위, 요소의 변형율 및 응력 등을 다시 구하였다. 처음 계산된 변위와 역계산으로 구한 변위를 비교함으로써 모델의 신뢰성을 평가하였다. 자동계측으로 라이닝의 비교적 정확한 계측을 수행하고 있는 지하철 한강 하저터널 현장에서 얻은 계측변위를 개발한 역해석 모델을 적용하여 실제 계측한 응력과 유사한 결과를 얻었다.

• 대한물리치료과학회지
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• 제16권3호
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• pp.55-66
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• 2009

Background: The purpose of this research was to investigate the factors affecting the low back pain of workers in hospital. 214 subjects waking at two general hospitals in Yosu city participated in this survey. Subjects consisted of doctors, nurses, medical engineers, officers and general laborers. The survey data were collected by a written questionnaire which made out by themselves for 25 days, from fourth August to 29th August, 2008. Methods: The questionnaire consisted of four categories, general, occupational, working habitual and the daily living characteristics. The collected data were analyzed by Chi-square test based on the present or absent of low back pain. Results: 1. In the general characteristics, low back pain had no significant relationship to all factors, sex, ago, body mass index, weight and height. 2. In the occupational characteristics, the phase of distribution of low back pain had statistical significant differences in the working hours a week, satisfaction of pay, satisfaction of occupation(p<0.05). However low back pain did not significantly related to the kind of occupation, period of work and degree of stress. 3. In the habitual characteristics, low back pain was significantly influenced by working posture, frequency of using lumbar and heavy material lifting, monotonous repetition of working operation and noise(p<0.05). No significant difference was shown in the factor of convenience of chair. 4. In the daily living characteristics, low back pain shown the significant differences in walking time a day, status of health and smoking pattern(p<0.05). there were, however, no significant differences in the aspect of the kind of house and bed, sleeping attitude, driving, riding time on the vehicle, exercising, frequency of cultural life and drinking alcohol. Conclusion: when I see above resultants totally, it appears a higher incidence caused by working environment rather than living habit and then consequently compared to hospital workers, they also have high incidence like others. In order to reduce incidence of low back pain and enjoy the our life we need to educate ourselves preventing program for low back pain and try to effort for preventing of low back pain on each department and individual.

• KIEAE Journal
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• 제16권3호
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• pp.121-128
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• 2016

Purpose: The vacuum glazing should constantly retain the gap in vacuum state to maintain high thermal performance. To do so, pillars are used to prevent the glazing from clinging to each other by the atmospheric pressure and therefore surface of the vacuum glazing is consistently affected by residual stress. The vacuum glazing could be applied to curtain wall systems at spandrel area to fulfill a rigorous domestic standard on U-value of the external wall. However, this can lead to high glazing temperature increase by heat concentration at a back panel and finally thermal stress breakage. This study experimentally determined weakness of the vacuum glazing systems on the thermal stress breakage and investigated effect of the residual stress. Method: The experiment first built two scale-down mock-up facilities that replicate the spandrel area in curtain wall, and then installed single low-e glass and vacuum glazing respectively. The two mock-up facilities were exposed to outside to induce the thermal stress breakage. Result: The experiment showed that the temperature occurred the thermal stress breakage was $114.4^{\circ}C$ for the single low-e glass and $118.9^{\circ}C$ for the vacuum glazing respectively. The result also showed the vacuum glazing reached the critical point earlier than the single low-e glass, which means that the vacuum glazing has high potential to occur the thermal shock breakage. In addition, the small temperature difference between two glazing indicates that the residual stress scarcely affects breakage of the vacuum glazing.

• The Korean Journal of Pain
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• 제2권1호
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• pp.78-84
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• 1989

Steroid and local anesthetics were injected into the epidural space through the posterior sacral foramen or lumbar approach in 4 patients for the purposes of relieving severe low back pain and radiculopathy. These patients were referred from other sections dealing with low back pain and radiculopathy, because one could not tolerate the surgical stress due to a heart problem, another two did not want the operation and the last had post-laminectomy status. All patients were satisfied with the results subjectively.