• Journal of the Korea institute for structural maintenance and inspection
• /
• v.11 no.2
• /
• pp.103-108
• /
• 2007

A stress measurement method of structural member using piezoelectric property and electrostatic voltmeter is presented. The electric potentials of the surface of the piezoelectric element, which are proportional to the strain ${\varepsilon}$ on the structural member, are measured by an electrostatic voltmeter during load cycling. The stress ${\sigma}$ is calculated by this strain ${\varepsilon}$. Moreover, a stress distribution measurement tape which can be used for the stress distribution measurement along a specified line on the surface of structural member is developed, and the surface potential was measured by an electric static voltmeter of non-contact type. The applicability of the stress distribution measurement tape is examined through experiments using a notched specimen under cyclic loading. The measured distributions of x, y and xy are compared with those calculated by FEM analysis.

• Annals of Occupational and Environmental Medicine
• /
• v.34
• /
• pp.13.1-13.11
• /
• 2022

Background: Work is an inseparable element of a person's life, and violence in the workplace has various effects on individual workers and companies. While most studies have focused on specific industries, very few studies have investigated the influence of workplace violence by co-workers. Therefore, this study aimed to evaluate the association between workplace violence and work-related depression/anxiety in various occupations by differentiating the perpetrators of violence as co-workers and clients. Methods: This study was conducted based on data from the 4th and 5th Korean Working Conditions Surveys (KWCS). The experience of workplace violence was classified in terms of the perpetrator: workplace violence by co-workers and that by clients. Work-related depression and anxiety were assessed using questions about health problems related to depression and anxiety and whether the problems were related to work. Descriptive statistics, χ² tests, and multiple logistic regression analyses were performed using the SPSS 26.0. Results: After adjusting for sociodemographic characteristics (age, education, income, subjective health status) and occupational characteristics (occupation, weekly working hours, type of employment, size of workplace, and shift work), male workers with experience of workplace violence by co-workers were found to be at a higher risk of work-related depression/anxiety (odds ratio [OR], 11.52; 95% confidence interval [CI], 8.65-15.36). The same was confirmed for female workers (OR, 10.89; 95% CI, 7.90-15.02). Conclusions: Employees who experienced workplace violence from co-workers were found to be more vulnerable to work-related depression/anxiety. Continuous contact between the victim and the perpetrator may occur, and the possibility of a secondary assault can frighten the victim. Appropriate prevention and intervention measures that focus on the perpetrators of violence are needed.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.44 no.2
• /
• pp.141-147
• /
• 2024

In this study, micro CT images were used to confirm the tensile fracture strength according to the pore distribution characteristics of 3D printed concrete. Unlike general specimens, concrete structures printed by 3D printing techniques have the direction of pores (voids) depending on the stacking direction and the presence of filaments contact surfaces. Accordingly, the pore distribution of 3D printed concrete specimens was analyzed through quantitative and qualitative methods, and the tensile strength by direction was analyzed through a finite element technique. It was confirmed that the pores inside the 3D printed specimen had directionality, resulting in their anisotropic behavior. This study aims to analyze the characteristics of 3D concrete printing specimen and correlate them with simulation-based mechanical properties to improve performance of 3D printed material and structure.

• Journal of the Korea Concrete Institute
• /
• v.26 no.4
• /
• pp.441-448
• /
• 2014

From several researches, recently, it was found that using hollowed precast concrete (HPC) column made more compact concrete casting in joint region possible than using normal solid PC (Precast concrete) column. Therefore, the rigidity of joints can be improved like those of monolithic reinforced concrete (RC). After filling the hollow with grout concrete, however, it is expected that the HPC column behaviors like composite structure since PC element and grout concrete have different materials as well as there is a contact surface between two elements. These may affect the structural behavior and strength of the composite column. A compressive strength test was performed for the HPC column with parameter of hollow ratio for the case with and without grout in the hollow and the result is presented in this paper. The hollow ratios in the test are 35, 50 and 59% of whole section of column. Concentrated axial force was applied to top of the specimens supported as pin connection for both ends. In addition, finite element (FE) analysis was performed to simulate the failure behavior of HPC column for axial compression. As a result, it was found that the hollow ratio did not affect the initial stiffness of HPC filled with grout regardless of the strength difference of HPC and grout. However the strength was increased inversely corresponding to the hollow ratio. The structural capacity of HPC without grout closely related to the hollow size. Especially, the local collapse governs the overall failure when the thickness of HPC is too thin. Based on these effect, a suitable equation was suggested for calculation of the compressive strength of HPC column with or without grout. FE analysis considering the contact surface between HPC and grout produced a good result matched to the test result.

• The Journal of Korean Academy of Prosthodontics
• /
• v.45 no.4
• /
• pp.506-521
• /
• 2007

Statement of problem: The cumulative success rate of wide implant is still controversial. Some previous reports have shown high success rate, and some other reports shown high failure rate. Purpose: The aim of this study was to analyze, and compare the biomechanics in wide implant system embeded in different width of crestal bone under different occlusal forces by finite element approach. Material and methods: Three-dimensional finite element models were created based on tracing of CT image of second premolar section of mandible with one implant embedded. One standard model (6mm-crestal bone width, 4.0mm implant diameter central position) was created. Varied crestal dimension(4, 6, 8 mm), different diameter of implants(3.3, 4.0, 5.5, 6.0mm), and buccal position implant models were generated. A 100-N vertical(L1) and 30 degree oblique load from lingual(L2) and buccal(L3) direction were applied to the occlusal surface of the crown. The analysis was performed for each load by means of the ANSYS V.9.0 program. Conclusion: 1. In all cases, maximum equivalent stress that applied $30^{\circ}$ oblique load around the alveolar bone crest was larger than that of the vertical load. Especially the equivalent stress that loaded obliquely in buccal side was larger. 2. In study of implant fixture diameter, stress around alveolar bone was decreased with the increase of implant diameter. In the vertical load, as the diameter of implant increased the equivalent stress decreased, but equivalent stress increased in case of the wide implant that have a little cortical bone in the buccal side. In the lateral oblique loading condition, the diameter of implant increased the equivalent stress decreased, but in the buccal oblique load, there was not significant difference between the 5.5mm and 6.0mm as the wide diameter implant. 3. In study of alveolar bone width, equivalent stress was decreased with the increase of alveolar bone width. In the vertical and oblique loading condition, the width of alveolar bone increased 6.0mm the equivalent stress decreased. But in the oblique loading condition, there was not a difference equivalent stress at more than 6.0mm of alveolar bone width. 4. In study of insertion position of implant fixture, even though the insertion position of implant fixture move there was not a difference equivalent stress, but in the case of little cortical bone in the buccal side, value of the equivalent stress was most unfavorable. 5. In all cases, it showed high stress around the top of fixture that contact cortical bone, but there was not a portion on the bottom of fixture that concentrate highly stress and play the role of stress dispersion. These results demonstrated that obtaining the more contact from the bucco-lingual cortical bone by installing wide diameter implant plays an important role in biomechanics.

• The Journal of Korean Academy of Prosthodontics
• /
• v.53 no.2
• /
• pp.120-127
• /
• 2015

Purpose: The aim was to investigate the effect of implant thread designs on the stress dissipation of the implant. Materials and methods: The threads evaluated in this study included the V-shaped, buttress, reverse buttress, and square-shaped threads, which were of the same size (depth). Building four different implant/bone complexes each consisting of an implant with one of the 4 different threads on its cylindrical body ($4.1mm{\times}10mm$), a force of 100 N was applied onto the top of implant abutment at $30^{\circ}$ with the implant axis. In order to simulate different osseointegration stages at the implant/bone interfaces, a nonlinear contact condition was used to simulate immature osseointegration and a bonding condition for mature osseointegration states. Results: Stress distribution pattern around the implant differed depending on the osseointegration states. Stress levels as well as the differences in the stress between the analysis models (with different threads) were higher in the case of the immature osseointegration state. Both the stress levels and the differences between analysis models became lower at the completely osseointegrated state. Stress dissipation characteristics of the V-shape thread was in the middle of the four threads in both the immature and mature states of osseointegration. These results indicated that implant thread design may have biomechanical impact on the implant bed bone until the osseointegration process has been finished. Conclusion: The stress dissipation characteristics of V-shape thread was in the middle of the four threads in both the immature and mature states of osseointegration.

• Journal of the Korean Society for Library and Information Science
• /
• v.10
• /
• pp.39-70
• /
• 1983

The concept of the public library defined by the Korean Library Association does not describe the current state of the Korean public library but describes the public libraries in the western society. Korean public library was formed after the western public library but it was modified and reconciled with the tradition of Korea. The difference between the concepts occured in the acculturation process of the Korean public library. According to the International Encyclopeadia of the Social Sciences, acculturation comprehends those phenomena which result when groups of individuals having different cultures come into continuous firsthand contact, with subsequent changes in the original cultural patterns of either of both groups. Korea opened its door to western world in 1876, and it began to contact with the western world. As the consequence, the concept of the public library of the West diffused to Lee Dynasty which were characterized by the confucianism and the extended family system. These two characteristics were against the public library concept and it could not function as it was and it had to be modified to fit to Korean society. The American public library was formed by the diffusion of English public library. The concept fitted in the colonial American society which was characterized by the Christianity and nuclear family system. Religion and family life were closely knitted together and they contributed much to the formation of the American public library. Also the society needed various information to form their new nation. The need of the public library grew and the public library repidly developed as the American society was urbanized and industrialized. The changes of Korean public library has passed the following process of acculturation. 1. The Korean culture contacted with Western world. 2. The public library concept diffused to Korea, but the people were illiterate and the need of the public library was for the preservation of the old books. The collection was not for people. 3. The function of the public library in Korea was altered slightly as several intellectuals who formed the first modern public library tried to literate Koreans as a means of liberation :from Japan through the library service. 4. The traditional libraries such as sodandg and hyangyo disorganized and finally disappeared as the traditional elements of the culture disappeared and the new cultural elements prevailed in Korea. 5. When the traditional elements of culture were disorganized, a reinterpretation of the diffused culture appeared. With the appearance of the vouth group which was not existed in the traditional society, cultural facilities for them were needed. They began to use public library as their reading rooms. This pattern has been institutionalized ever since in Korean public library. 6. When the new element of the culture spread, the traditional cultural elements react against this element. As the new public libraries sprung out, there were movements to restore the old Korean tradition of the family libraries and Hyangyo to counteract to the new libraries. This movements were not successful and they all disappeared as they could not keep up the rapid social change occurred in the Korean society. 7. In the process of the cultral change, cultural lag occurred between the public library and the users who could not adopt to the new library. This has been continued to the present time. 8. This diffused concept of the public library was modified and became native to Korean society. However, the acculturation of the public library concept has not changed the traditional ideas of Korean people and their behavior. The Korean society recently has been changing rapidly and the function of the Korean public library is improving accordingly; 1. The extended Korean family system is disorganizing. As the consequence, the public library could substitute the family system offering information and recreation service, etc. 2. The growth of educated population is requiring a variety of library materials. An individual library can not meet the needs of them and cooperative library service will be needed to share resources. The public library will become the center of the cooperative service. 3. The Koreans are watching TV more hours than they read printed materials. For them, the public library needs to collect audiovisual materials. Especially the teaching materials should be all audiovisualized for the effective teaching. 4. Technology is developing rapidly in Korea, especially computer technology is applied in many parts of the society. This will also influence library service. The public library will be developing as the centralized library computer system. When the Korean public library functions as the extended family system and the center of the cooperative library system, the Korean public library will be functioning as the public library defined by the Korean Library Association.

• Proceedings of the Korean Geotechical Society Conference
• /
• 1998.05a
• /
• pp.35-81
• /
• 1998

Distinct Element Method(DEM) has a great advantage to model the discontinuous behaviour of jointed rock masses such as rotation, sliding, and separation of rock blocks. Geometrical data of joints by a field monitoring is not enough to model the jointed rock mass though the results of DE analysis for the jointed rock mass is most sensitive to the distributional properties of joints. Also, it is important to use a properly joint law in evaluating the stability of a jointed rock mass because the joint is considered as the contact between blocks in DEM. In this study, a stochastic modelling technique is developed and the dilatant rock joint is numerically modelled in order to consider th geometrical and mechanical properties of joints in DE analysis. The stochastic modelling technique provides a assemblage of rock blocks by reproducing the joint distribution from insufficient joint data. Numerical Modelling of joint dilatancy in a edge-edge contact of DEM enable to consider not only mechanical properties but also various boundary conditions of joint. Preprocess Procedure for a stochastic DE model is composed of a statistical process of raw data of joints, a joint generation, and a block boundary generation. This stochastic DE model is used to analyze the effect of deviations of geometrical joint parameters on .the behaviour of jointed rock masses. This modelling method may be one tool for the consistency of DE analysis because it keeps the objectivity of the numerical model. In the joint constitutive law with a dilatancy, the normal and shear behaviour of a joint are fully coupled due to dilatation. It is easy to quantify the input Parameters used in the joint law from laboratory tests. The boundary effect on the behaviour of a joint is verified from shear tests under CNL and CNS using the numerical model of a single joint. The numerical model developed is applied to jointed rock masses to evaluate the effect of joint dilation on tunnel stability.

• Journal of Korean Society of Environmental Engineers
• /
• v.27 no.4
• /
• pp.414-419
• /
• 2005

This study was performed to compare the treatment efficiencies of two media, newly developed Bio-rock and conventional gravel, in soil clothing contact oxidation process. The composition of synthetic wastewater were $COD_{Cr}$ $150{\sim}370\;mg/L$, $BOD_5$ $150{\sim}270\;mg/L$, T-N $20{\sim}60\;mg/L$, T-P $5{\sim}25\;mg/L$, pH 7 and 2 mL/L of trace element solution. The experiment using two reactors was comparatively conducted for the flow rate of 40 L/d for 13 months, respectively. Initially Bio-rock reactor was increased to pH 12 due to $Ca(OH)_2$ with hydration of cement, but gravel reactor was dropped to pH 4 due to the degradation of organic material and nitrification. This significant pH variation deteriorated the growth and activity of microorganism. But the high pH of Bio-rock seems favorite to ammonia stripping and precipitation of phosphate. Such pH variation of Bio-rock and gravel reactors were finally stabilized to pH 8 and pH 6, respectively. The removal efficiencies of organic compounds from Bio-rock reactor were 96% of $COD_{Cr}$, 98% of $BOD_5$, 80% of T-N and 85% of T-P which stably coping against variation of influent concentration. But those of gravel reactor were 96% of $COD_{Cr}$, 96% of $BOD_5$, 42% of T-N and 40% of T-P, respectively. The Bio-rock was 2 times higher than T-N and T-P in treatment efficiency. And electron-microscopic examination showed that Bio-rock was more favorable to microbial adherence than gravel. The microbial populations were $5.2{\times}10^6\;CFU/mL$ of Bio-rock reactor compared to $2.6{\times}10^6\;CFU/mL$ in gravel reactor. In result Bio-rock was favor to microbial adherence and high treatment efficiency in spite of variation of influent concentration which had the advantages in saving running time and reducing site requirement.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.34 no.4
• /
• pp.297-305
• /
• 2018

Purpose: This study aimed to analyze stress distribution and maximum von Mises stress generated in intracoronal restorations and in tooth structures of mandibular molars with various types of cavity designs and materials. Materials and Methods: Three-dimensional solid models of mandible molar such as O inlay cavity with composite and gold (OR-C, OG-C), MO inlay cavity with composite and gold (MR-C, MG-C), and minimal invasive cavity on occlusal and proximal surfaces (OR-M, MR-M) were designed. To simulate masticatory force, static axial load with total force of 200 N was applied on the tooth at 10 occlusal contact points. A finite element analysis was performed to predict stress distribution generated by occlusal loading. Results: Restorations with minimal cavity design generated significantly lower values of von Mises stress (OR-M model: 26.8 MPa; MR-M model: 72.7 MPa) compared to those with conventional cavity design (341.9 MPa to 397.2 MPa). In tooth structure, magnitudes of maximum von Mises stresses were similar among models with conventional design (372.8 - 412.9 MPa) and models with minimal cavity design (361.1 - 384.4 MPa). Conclusion: Minimal invasive models generated smaller maximum von Mises stresses within restorations. Within the enamel, similar maximum von Mises stresses were observed for models with minimal cavity design and those with conventional design.