• Magazine of the Korean Society of Agricultural Engineers
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• v.34 no.3
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• pp.53-63
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• 1992

To investgate the fracture behavior of the steel fiber reinforced concreate, the specimens with different steel fiber contents of 0.0%, 0.5%, 1.0%, 1.5%, were made and notched with differents notch depth ratios of 0.0,0.2, 0.4, 0.6, and the three point bend tests were followed. Test results of 16 different types of above combined specimens were summarized as follows. 1.The load line deflection contents were found to increase 5%, 16%, 19%, respectively, compared to the unnotched specimen with the increased of initial notch depth ratio to 0.2,0.4, 0.6, respectively. 2.The frexural strength were found to decrease 14%, 16%, 21 %, respectively, compared to the unnotched specimen with the increase of initial notch depth ratio to 0.2, 0.4, 0.6,respectively. 3.The stress intensity factors of the steel fiber reinforced concrete were found to increase 1.1 1.5 1.9 times, respectively, compared to the concrete with no steel fiber content with the increase of fiber content to 0.5%, 1.0%, 1.5%, respectively. 4.The influence of the mass of the steel fiber reinforced concrete to the whole fracture energy was found to be minor with 6~8 % contribution. 5.The fracture energy of the steel fiber reinforced concrete, considering the load-deflection curve and concrete mass was found to be approximately 350-380kg m/m$^2$. 6.The regression analysis through the relationship between the compressive(Oc)/tensile (OT) strength and fracture energy(Gf) showed that the fracture energy of the steel fiber reinforced concrete could be predicted as follows. Gf= 19.2662 Oc - 3940.4 Gf= 246.876 OT- 6008.8

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.2
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• pp.179-188
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• 2011

Steel structures have been allowed to have fatigue damage tolerance in fact. If it would be assessed whether fatigue crack is growing or not and How fast fatigue crack is propagating, we should make a rational decision on methods and a period of reinforcement in the maintenance. In this study, fatigue crack growth tests on two kinds of through-thickness cracked steel plates and a out-of-plane gusset welded joint were conducted to evaluate fatigue crack growth rate using the COD(Crack Opening Displacement), and COD measurement using strain gauges was examined to offer a practical method. As a result, we proposed a reasonable assessing method for fatigue crack growth rate using the COD and it was experimentally proved practical to estimate the COD through measuring strains.

• Safety and Health at Work
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• v.9 no.2
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• pp.216-223
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• 2018

Background: Many studies have reported negative psychological or physical effects of emotional labor. Relationship between work-related musculoskeletal disorder and psychosocial factors has been reported. To manage organizational and psychosocial factors of musculoskeletal disorder with work place intervention among emotional laborers, the factors contributing to musculoskeletal pain must be identified and clarified. Methods: Data from the fourth Korean Working Conditions Survey was analyzed. Based on the questionnaire, we selected emotional laborers and included 3,979 participants, excluding participants whose variables were of interest to the researcher. Weight variable was applied. The association with musculoskeletal pain and psychosocial factors, such as workload, monotonous work, job control, social support, and job satisfaction, was investigated. Results: Univariate analysis demonstrated that there was a statistically significant relationship between social support, job satisfaction, and musculoskeletal pain. In multivariate analysis, job satisfaction showed a strong correlation with musculoskeletal pain at all sites. Social support was significantly associated with backache. Monotonous work seemed to reduce the pain in the neck and/or upper limbs. Job control and work intensity were not significantly associated with musculoskeletal pain. Conclusion: In this study, job satisfaction was significantly associated with musculoskeletal pain, and social support among the social psychological stressors could reduce musculoskeletal pain. However, unlike previously known, the presence of monotonous work resulted in reduced musculoskeletal pain. The results of this study will help to establish the direction of improvement of atmosphere in the workplace to prevent the musculoskeletal pain of emotional laborers.

• Safety and Health at Work
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• v.9 no.2
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• pp.224-231
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• 2018

Background: Organizations are pursing complex and diverse aims to generate higher profits. Many workers experience high work intensity such as workload and work pressure in this organizational environment. Especially, psychological burden is a commonly used term in workplace of Republic of Korea. This study focused on defining the psychological burden from the perspective of occupational safety and health and tried to develop a scale for psychological burden. Methods: The 48 preliminary questionnaire items for psychological burden were prepared by a focus group interview with 16 workers through the Copenhagen Psychosocial Questionnaire II and Mindful Awareness Attention Scale. The preliminary items were surveyed with 572 workers, and exploratory factor analysis, confirmatory factor analysis, and correlation analysis were conducted for a new scale. Results: As a result of the exploratory factor analysis, five factors were extracted: organizational activity, human error, safety and health workload, work attitude, and negative self-management. These factors had significant correlations and reliability, and the stability of the model for validity was confirmed using confirmatory factor analysis. Conclusion: The developed scale for psychological burden can measure workers' psychological burden in relation to safety and health. Despite some limitations, this study has applicability in the workplace, given the relatively small-sized questionnaire.

• Nuclear Engineering and Technology
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• v.51 no.8
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• pp.1905-1915
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• 2019

This paper investigated the influence of simple support girds on flow, irrespective of having mixing vanes, in a 1 × 3 array rod bundle by using CFD methodology and the most accurate turbulence model which could reflect the actual physics of the flow was determined. In this context, a CFD model was created simulating the experimental studies on a single-phase flow [1] and the results were compared with the experimental data. In the first part of the study, influence of mesh was examined. Tetra, hybrid and poly type meshes were analyzed and convergence study was carried out on each in order to determine the most appropriate type and density. k - ε Standard and RSM LPS turbulence models were used in this section. In the second part of the study, the most appropriate turbulence model that could reflect the physics of the actual flow was investigated. RANS based turbulence models were examined using the mesh that was determined in the first part. Velocity and turbulence intensity results obtained on the upstream and downstream of the spacer grid at -3d_h, +3d_h and +40d_h locations were compared with the experimental data. In the last section of the study, the behavior of flow through the spacer grid was examined and its prominent aspects were highlighted on the most appropriate turbulence model determined in the second part. Results of the study revealed the importance of mesh type. Hybrid mesh having the largest number of structured elements performed remarkably better than the other two on results. While comparisons of numerical and experimental results showed an overall agreement within all turbulence models, RSM LPS presented better results than the others. Lastly, physical appearance of the flow through spacer grids revealed that springs has more influence on flow than dimples and induces transient flow behaviors. As a result, flow through a simple support grid was examined and the most appropriate turbulence model reflecting the actual physics of the flow was determined.

• Polymer(Korea)
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• v.39 no.2
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• pp.219-224
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• 2015

In this work, the effect of fiber array direction including $0^{\circ}$, $0^{\circ}/90^{\circ}$, $0^{\circ}/45^{\circ}/-45^{\circ}$ was investigated for mechanical properties of basalt fiber-reinforced composites. Mechanical properties of the composites were studied using interlaminar shear strength (ILSS) and critical stress intensity factor ($K_{IC}$) measurements. The cross-section morphologies of basalt fiber-reinforced epoxy composites were observed by scanning electron microscope (SEM). Also, the surface properties of basalt fibers were determined by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). From the results, it was observed that acid treated basalt fiber-reinforced composites showed significantly higher mechanical interfacial properties than those of untreated basalt fiber-reinforced composites. These results indicated that the hydroxyl functional groups of basalt fibers lead to the improvement of the mechanical interfacial properties of basalt fibers/epoxy composites in the all array direction.

• Journal of the Korean Wood Science and Technology
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• v.20 no.2
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• pp.61-72
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• 1992

This study was carried out to investigate the fracture behavior and the fracture criterion of yellow lauan(Shorea spp.), when has used for furniture and wood structures, and to offer a reliability for wood structure and basic data for wood fracture criterion in experiments which are fracture tested under mode I, mode II and mixed mode loading condition. The results were summarized as follows; 1. Fractures in specimens which have inclined grain in yellow lauan procedeed from crack tip in the radial direction along the grain. 2. In yellow lauan, $K_{IC}RL$ was 42.1kg/$cm^{3/2}$ and $K_{IIC}RL$ was 15.8kg/$cm^{3/2}$. 3. The fracture criteria of lauan were; ($K_I/K_{IC}$)+($K_{II}/K_{IIC}$)=1 in RL system with inclined grain at $45^{\circ}$, ($K_I/K_{IC}$)+$(K_{II}/K_{IIC})^2$=1 with inclined grain at $15^{\circ}$ and $(K_I/K_{IC})^2$+$(K_{II}/K_{IIC})^2$=1 with inclined grain at $30^{\circ}$, $60^{\circ}$, $75^{\circ}$ and $90^{\circ}$, respectively. 4. The fracture criterion of wood could vary with the species, and the load applying condition. In order to measure the fracture criterion strictly, along with standardization of specimen geometry a large amount of experimental data is needed. 5. $K_{IC}$(critical stress intensity factor) can be predicted by grain angle. As the grain inclined angle increased, $K_{IC}$ and $K_{IIC}$ are increased.

• Journal of the Korea Safety Management & Science
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• v.19 no.3
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• pp.71-79
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• 2017

The purpose of this study was to identify the observable symptoms of musculoskeletal disease from electronic components manufacturing workers who involved in many repetitive tasks and to provide the basic data for the prevention and management. The survey was conducted on 721 people from 15 April, 2013 to 17 May, 2013 by self­recording type. The results of the study are as follows. First, symptom complaints based on different body parts are in following order, waist was 12.9%, shoulder was 10.5%, neck was 7.4%, hand/wrist/finger was 7.4%, leg/foot was 4.4%, arm/elbow was 2.8%, and 21.9% of the respondents showed symptoms in more than one body part. Sex, age, marital status, work experience, work intensity, and past accident experience were statistically significant. Second, in the job stress evaluation, all male and female workers were below the median of Korean workers in all of 8 categories. the higher the scores for lack of job autonomy, the higher the symptom complaints of musculoskeletal disease. In the case of patients complain observable symptoms of musculorskeletal disease, they should receive proper outpatient treatment, various programs such as stretching by body parts, setting up a desirable working posture, switching to cyclical work, should b developed as much as possible.

• Korean Journal of Community Nutrition
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• v.7 no.4
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• pp.495-505
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• 2002

A study was performed to develop as a screening tool the Simple Evaluation Questionnaire for Screening the Over-weight-type Dietary Pattern in 30 to 49 Year Old Adults. We used the data from the 30 to 49 year old subjects who participated in the three surveys - the health behavior survey, the dietary habit survey and the food intake survey - as the National Health and Nutrition Survey 1998. The 3,598 adults were classified into to two body fatness groups of normal (including underweight) and overweight (including obese) on the basis of their relative body weight (RBW) When comparing variables between the two groups, significant differences were found in gender, education, job, employment status, perceived health status, sadness / depression state, stress level, age, number of diseases, age when overweightedness started, maximum body weight, sleep length, drinking pattern (yes/no) , amount of alcoholic drinks, frequency of intoxication or drunkeness, amount of alcoholic drinks when drunk, intensity of exercise, frequency of exercise, exercise duration, skipped meals, small meals and drug supplements. In terms of food intake, there were significant differences in the daily food intake in terms of breakfast, dinner, daily kimchi and dairy products. In terms of mealtimes, we found differences in the amount of cooked rice at breakfast, kimchi at lunch, soup / kuk at dinner, fresh vegetables for snacks, fried foods for snacks between breakfast and lunch, and fruits /juices for snacks between lunch and dinner. After developing questions with indicators and analyzing the indicators by logistic regression analysis three times, we chose 10 questions for a simple evaluation of dietary patterns for the overweight-type category in order to give one point each. Among them we selected two questions to add one additional point and one question to add two additional points. The average scores of the overweight and normal groups, as shown by the developed questionnaire, were $5.97 \pm 2.36 \pm 7.36 \pm 2.21$, respectively. A score of seven points was selected as the cut-off point. We examined the sensitivity, specificity and positive predictive value of the questionnaire to the results of 67%, 59% and 62%, respectively.

• Journal of Environmental Science International
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• v.8 no.6
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• pp.669-676
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• 1999

The effects of wounding and jasmonic acid(JA) on polyphenol oxidase(PPO) in tomato(Lycopersicon esculentum Mill.) seedlings were investigated. PPO was strongly induced by wounding or JA, and the response was also shown to be systemically induced by wounding. Mechanical wounding in cotyledon or leaf produced a signal that caused the concentration of PPO to increase in the unwounded cotyledon, in the first leaves but not in the second leaves. Severity of wounding and light intensity also affected wound induced change in PPO activity, JA showed a stimulatory effect on the loss of chlorophyll and the rapid increase in PPO activity. The PPO was clearly more active in the wounded leaves than in controls. The potency and specificity of the JA indicate a close relationship between JA and wound-induced changes in PPO in tomato species. JA and abscisic acid(ABA) acted similarly on both unwounded and wounded leaves, but the amount of PPO in the wounded leaves was always more than the respective controls. The highest increase in PPO activity occurred in woundand JA-induced leaves of seedlings kept under bright lighting. Benzyladenine(BA) completely abolished JA- and ABA-induced PPO activity. The results suggest that JA-induced PPO activity is due to de novo PPO synthesis. Histochemical tests for PPO in stems of wound- and JA -treated tomato plants indicate that PPO was localized primarily, in the. outer .cortex . and xylem parenchyma. It is concluded that exogenously applied JA acts as stress agents and PPO may be a component of the inducible anti-hervivore defense response.