• Coupled systems mechanics
• /
• v.13 no.4
• /
• pp.311-335
• /
• 2024

This work aims to show a model to estimate the minimum cost (Thickness and area of steel in X and Y directions) for design a circular isolated footing with eccentric column that considers that the surface in contact with the ground works partially under compression. The formulation is shown by integration to find the moments, the bending shears and the punching shear using the pressure volume under the footing. Some researchers show the minimum cost design for circular isolated footings for an eccentric column assuming that the contact area works completely in compression, others consider the contact surface with the ground working partially in compression for a column in the center of the base. Three numerical examples are developed to obtain the complete design, which are: Example 1 for a column in the center of the base,Example 2 for a column at a distance of 1.50 m from the center of the base in the X direction, Example 3 for a column at a distance of 1.50 m from the center of the base in both directions. Also, a comparison of the new model against the model proposed by other authors is presented. The comparison shows that the new model generates a great saving of up to 43.74% for minimum area and 48.44% for minimum cost design in a column located in the center of the base, and when the column is located at a distance of radius/2 starting from the center of the base in the X direction generates great savings of up to 45.24% for minimum area and 31.80% for minimum cost design. Therefore, it is advisable to use the model presented in this study.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.28 no.7
• /
• pp.1267-1273
• /
• 2022

Although the Korea shipbuilding industry has recently been receiving most of the orders for ships in the world, production processes are being disrupted due to a shortage of manpower at the production site. This is because the workers quit the shipyard as both work and wages were reduced due to the long slump in the shipbuilding industry. The main reason for the increase in orders was the large-scale orders for Qatar LNG carriers, and the situation in which the technical specifications required for ships are becoming more complex is also working to an advantage. Because the contract delivery time is of utmost importance for ships, the dock launch plan is the most important management item among the shipyard's major processes. The structure to be built in the dock may be a hull that has left the design work or a finished vessel, and in some cases, it is often at the level of some blocks of the hull. When launching, the hull is affected by the hogging or sagging moment due to the fluid force, and securing the safety of the structural strength of the block connection is of utmost importance. In a normal process, the connecting member launches after welding has been completed, but in actual shipbuilders, quick decision-making is needed on the conditions for securing structural safety to comply with the docking schedule. In this study, a detailed analysis method and applicability using a bending stress evaluation method and finite element analysis modelling were analyzed to rationally judge the above-mentioned problems from an engineering point of view. The main contents mentioned in the thesis can be used as good examples when conducting similar structural strength evaluations in the future.

• Journal of the Korean Ceramic Society
• /
• v.34 no.1
• /
• pp.56-62
• /
• 1997

The PAN (Polyacrylonitrile) based carbon fiber-ceramic composites (CFCC) were prepared from mixtures of short carbon fibers, phenolic resin and ceramic binder. The effects of carbonization temperature of a pre-cursor fiber, the stabilized PAN fiber, on the specific surface area and the bending strength of the activated CFCC were studied in this work. The precursor fiber was carbonized at 80$0^{\circ}C$ and 100$0^{\circ}C$, respectively. The CFCC were activated at 85$0^{\circ}C$ in carbon dioxide for 10~90 minutes. As the burn-off of the activated CFCC made of the precursor fiber carbonized at 80$0^{\circ}C$ was increased from 37% to 76%, the specific surface area in-creased from 493m2/g to 1090m2/g, and the bending strength decreased from 4.5MPa to 1.4MPa. These values were about two times larger than those of the activated CFCC of which precursor fiber was car-bonized at 100$0^{\circ}C$. The effects of carbonization temperature of a precursor fiber on the specific surface area and bending strength of the activated CCFC were explained by bonding force between carbon fiber and car-bonized phenolic resin as well as by relative shirnkage between carbon fiber and ceramic film.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.301-304
• /
• 2008

The stair joints constructed with prefabricated system are general method doing structure design at hinge. If you regarded joints to come in contact with a flight of stairs and a slope of stairs as hinge, the moment performance of joints is not in the least moment, so as the bending moment of the stair case is increased, the reinforcement increase. Also the use is decreased because increasing the joint damage of the vibration & fatigue load. No less the reason constructed with pin the stair joints because the construction efficiency of field work is useable. Recently, they are considering the construction efficiency, while the semi-rigid detail for bending performance of joints is proposed, but for now they don't reflect the detail. Therefore, we proposed that reflecting the method at design semi-rigid joints. We compared the moment performance with the stair joints designed at the rigid joints, semi-rigid joints and pin joints. The nonlinear behavior of staircase core statically indeterminate structure. The result of research is that a bending stiffness modulus bring to reflect the semi-rigid performance, the performance of the semi-rigid joint is better than pin joints, and that is judged the system better seismic and vibration performance because have excellent ductility more than rigid joint.

• Journal of the Microelectronics and Packaging Society
• /
• v.28 no.2
• /
• pp.89-94
• /
• 2021

The mechanical reliability of flexible devices has become a major concern on their commercialization, where the importance of reliable bonding is highlighted. In terms of component materials' properties, it is important to consider thermal damage of polymer substrates that occupy large area of the flexible device. Therefore, room temperature bonding process is highly advantageous for implementing flexible device assemblies with mechanical reliability. Conventional epoxy resins for the bonding still require curing at high temperatures. Even after the curing procedure, the bonding joint loses flexibility and exhibits poor fatigue durability. To solve this problems, low-temperature and adhesive-free bonding are required. In this work, we develop a room temperature bonding process for polymer substrates using carbon nanotube heated by microwave irradiations. After depositing multiple-wall carbon nanotubes (MWNTs) on PET polymer substrates, they are heated locally with by microwave while the entire bonding specimen maintains room temperature and the heating induces mechanical entanglement of CNT-PET. The room temperature bonding was conducted for a PET/CNT/PET specimen at 600 watt of microwave power for 10 seconds. Thickness of the CNT bonding joint was very thin that it obtains flexibility as well. In order to evaluate the mechanical reliability of the joint specimen, we performed lap shear test, three-point bending test, and dynamic bending test, and confirmed excellent joint strength, flexibility, and bending durability from each test.

• Research in Community and Public Health Nursing
• /
• v.6 no.2
• /
• pp.319-334
• /
• 1995

To investigate the risk factors of low back pain, an epidemiological study was carried out among male workers aged 20-55 employed in an automobile industry in Korea during the time period from February 1993 to October 1995. Workers participated to this study were divided into low back pain group(LBP) and control group, according to the self-reports by written questionnaires. General characteristics, medical history, work related factors, fatigue, and MMPI were compared between two groups. To clarify the relationship between job related low back pain and radiologic features of lumbar spine, radiographic study was carried out. The resultant data were processed for $x^2-test$, t-test, and stepwise logistic regression to confirm the adjusted odds ratios. The results were as follows: 1. History of back disease, lifting and carrying work, excessive physical fatigue, and weakend back strength of individual workers were directly associated with low back pain. Odd ratios of these 4 risk factors of low back pain were 5.07, 3.34, 1.49, and 1.22 respectively. 2. The frequency of low back pain history was significantly higher in LBP group. 3. Back muscle strength of lumbar spine of LBP group were significantly lower than control group. 4. The workers in LBP group revealed high fatigue symptoms. 5. In MMPI test LBP group showed higher scales in hypochondriasis, depression, hysteria, psychopathic deviate, paranoia, psychasthenia, schizophrenia, and hypomania. 6. LBP group were more frequently involved in lifting and carrying, working in awkward position, bending, twisting and using lower extremities. 7. LBP group were exposed more to vibration during working. 8. In the Analysis of radiographs of lumbar spine, Jacob's line not crossing fourth lumhar disc space, transitional vertebrae and lumbar displacement more than 4.4mm in standing lateral view were more frequently observed in LBP group than control group. Through these results, it is concluded that identification of previous history of back problem, change of work or working environment for workers with previous back problem and measures to relieve both physical and psychological fatigue of the workers are required for optimal management of work-related back problems among workers. In the present study, several results were different from the previous reports: Jacob's line not corssing fourth lumbar disc space, lumbarization, and vertebral slipping (spondylolisthesis) more than 4.4mm are related to backache. Meticulous studies are required to elucidate the difference.

• Journal of the Korean Society of Clothing and Textiles
• /
• v.32 no.10
• /
• pp.1584-1594
• /
• 2008

This study was to research the characteristics of the body shape of Korean woman farmers by the major crops. Four hundred ninety-five Korean woman farmers from 9 different area such as Kumi, Damyang, Iksan, Injae, Chungju, Choongju, Haman, Whasung, and Whasoon volunteered for this study. Their major crops were the rice, the pepper, the water melon, the strawberry, the wild rocambole, the sweet persimmon, the grapes, the mushroom, and the chrysanthemums. Twelve body angles were measured from archived the somatotype photographs of the front, the side, and the back. Questionnaires of SF-36 and the farmer's symptom, and the farm-work related movements were surveyed. The results were as follows; 1. Farmers had lower health levels in physical role limit, pain, vitality, and physical function than other occupational workers. 2. Most farmers acted the high-risk ergonomics motions when they worked in the farm. 3. There were significantly different on the both shoulder angles, the hip tangential line slope, the hip breadth angel, in frontal ankle-knee angle, the bending back angle, the dropping breast slope, the abdominis media angle, under the abdominis media angle, the glutea angle, under the glutea angle, and the sideward knee angle(p<.05). 4. Farmers cultivating the low plants such as the water melon, the strawberry, and the wild rocambole showed more banded vertebralis and side knee angles. Farmers cultivating the red pepper showed the dropping the left shoulder and O shape legs. Farmers cultivating the fruit trees such as the sweet persimmon and the grapes showed the less banded side knee angles than other farmer groups. 5. On comparing the same age, farmers showed the older's body shape in earlier and much more than the old living in the city.

• Steel and Composite Structures
• /
• v.29 no.3
• /
• pp.379-389
• /
• 2018

In this research, the explicit closed-form local buckling solution of steel plates in contact with concrete, with both loaded and unloaded edges elastically restrained against rotation and subjected to eccentric compression is presented. The Rayleigh-Rize approach is applied to establish the eigenvalue problem for the local buckling performance. Buckling shape which combines trigonometric and biquadratic functions is introduced according to that used by Qin et al. (2017) on steel plate buckling under uniform compression. Explicit solutions for predicting the local buckling stress of steel plate are obtained in terms of the rotational stiffness. Based on different boundary conditions, simply yet explicit local buckling solutions are discussed in details. The proposed formulas are validated against previous research and finite element results. The influences of the loading stress gradient parameter, the aspect ratio, and the rotational stiffness on the local buckling stress resultants of steel plates with different boundary conditions were evaluated. This work can be considered as an alternative to apply a different buckling shape function to study the buckling problem of steel plate under eccentric compression comparing to the work by Qin et al. (2018), and the results are found to be in consistent with those in Qin et al. (2018).

• Coupled systems mechanics
• /
• v.7 no.2
• /
• pp.197-209
• /
• 2018

Fiber-reinforced concrete (FRC) is a material with increasing application in civil engineering. Here it is assumed that the material consists of a great number of rather small fibers embedded into the concrete matrix. It would be advantageous to predict the mechanical properties of FRC using nondestructive testing; unfortunately, many testing methods for concrete are not applicable to FRC. In addition, design methods for FRC are either inaccurate or complicated. In three-point bending tests of FRC prisms, it has been observed that fiber reinforcement does not break but simply pulls out during specimen failure. Following that observation, this work is based on an assumption that the main components of a simple and rather accurate FRC model are mechanical properties of the concrete matrix and fiber pullout force. Properties of the concrete matrix could be determined from measurements on samples taken during concrete production, and fiber pullout force could be measured on samples with individual fibers embedded into concrete. However, there is no clear relationship between measurements on individual samples of concrete matrix with a single fiber and properties of the produced FRC. This work presents an inverse model for FRC that establishes a relation between parameters measured on individual material samples and properties of a structure made of the composite material. However, a deterministic relationship is clearly not possible since only a single beam specimen of 60 cm could easily contain over 100000 fibers. Our inverse model assumes that the probability density function of individual fiber properties is known, and that the global sample load-displacement curve is obtained from the experiment. Thus, each fiber is stochastically characterized and accordingly parameterized. A relationship between fiber parameters and global load-displacement response, the so-called forward model, is established. From the forward model, based on Levenberg-Marquardt procedure, the inverse model is formulated and successfully applied.

• Journal of the Ergonomics Society of Korea
• /
• v.30 no.3
• /
• pp.409-418
• /
• 2011

Objective: This study was performed to evaluate the child-care teachers' job in relation to physical work. Background: Child-care teacher is directly related to the quality of child care. And their physical activity is higher than general education teachers because the proportion of day care is high. But analyzes of child-care teachers' job burdens and the work environment associated with physical activity is not well established. Method: To conduct this study, the child-care teachers' job was classified into 18 physical works. After classification, posture was evaluated by ergonomic posture evaluation schemes of OWAS, RULA, REBA and evaluated for each physical part. Next, musculoskeletal subjective symptoms were analyzed. Results: The results showed the following: The highest assessment on the posture evaluation was "helping children to ride a school bus", "feeding: meal/snack", "brushing children's teeth" and "arrangement of nap-stuff". The rank of high-risk assessment on the neck/trunk/leg part was arranged by: "feeding: meal/snack", "helping children to ride a school bus", "making nap", "arrangement nap-stuff" and "brushing children's teeth". The rank of high-risk assessment on the upper limbs part was arranged by: "helping children to ride a school bus", "the bust - group activity", "meal/snack time - preparing, feeding, arrangement", "nap time - preparing, arrangement", "brushing children's teeth", and "using the toilet". According to the results of each musculoskeletal subjective symptom, teachers ordered the pain area as follows: waist, shoulder, leg/feet, and neck, and they showed more pain on trunk than the upper limbs. Conclusion: To sum up the results from ergonomic posture evaluation and a subjective symptom, the following are high working pressures: "feeding: meal/snack", "the bust - group activity", "making nap", "brushing children's teeth" with deep bending and waist twisting, "helping children to ride a school bus", "brushing children's teeth" with lifting shoulder; "meal/snack time - preparing, arrangement", "nap time - preparing, arrangement", and "using the toilet" with moving or an up-down position in their job. Application: The results of this study might be information for improvement of the child-care teachers' job environment.