• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.425-431
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• 2015

LNG (liquefied natural gas) is considered the best alternative eco-fuel, and many studies on the LNG fuel system have been performed to use LNG as the fuel for ships. For the LNG fuel supply system, natural gas transfers from the vaporizer to the engine in the gaseous state with a temperature of $50^{\circ}C$ and a pressure of 35MPa. Therefore, a structural safety evaluation of the double-walled pipelines considering thermal load is essential. In this article, an uniaxial tensile test for super duplex stainless steel, material for double-walled pipe, according to the annealing time was carried out to analyze the thermal effect. In addition, thermo-structural analysis of the high temperature-high pressure double-walled pipe with fixed supports that are now used widely was carried out to evaluate the structural safety. To minimize stress concentration of the connection point between the support and inner pipe, the shapes of the new type support that can slip through inner pipe were proposed, and the supports which has best structural performance was selected using the results from the thermo-structural analyses of new supports and an analysis of the whole double-walled pipeline was performed to ensure structural safety. These results can be used as a database for the design of double-walled pipelines and sliding support.

• Journal of the Korean Geotechnical Society
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• v.32 no.9
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• pp.51-62
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• 2016

Parametric studies for various site conditions by using 3d numerical model were carried out in order to estimate dynamic behavior of soil-pile-structure system in dry soil deposits. Proposed model was analyzed in time domain using FLAC3D which is commercial finite difference code to properly simulate nonlinear response of soil under strong earthquake. Mohr-Coulomb criterion was adopted as soil constitutive model. Soil nonlinearity was considered by adopting the hysteretic damping model, and an interface model which can simulate separation and slip between soil and pile was adopted. Simplified continuum modeling was used as boundary condition to reduce analysis time. Also, initial shear modulus and yield depth were appropriately determined for accurate simulation of system's nonlinear behavior. Parametric study was performed by varying weight of superstructure, pile length, pile head fixity, soil relative density with proposed numerical model. From the results of parametric study, it is identified that inertial force induced by superstructure is dominant on dynamic behavior of soil-pile-structure system and effect of kinematic force induced by soil movement was relatively small. Difference in dynamic behavior according to the pile length and pile head fixity was also numerically investigated.

• Korean Journal of Health Education and Promotion
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• v.19 no.2
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• pp.57-72
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• 2002

Students spend most of their time in school. Schools have the possibility of unanticipated accidents, however, and the rate of accidents in schools is increasing. The purpose of this study were to understand the accidents that arise in schools as well as the school safety management system and by analyzing affects that school safety management system has on accidents in schools, to come lip with a preventive plan. 906 high school sophomore students attending in Seoul were surveyed 1Tom November 12th to 23rd 2001. The results were following: 1. Students surveyed comprised of the following: Male 48.9%, Female 51.1% Public Schools 32.6%, Private Schools 67.4% Boys Schools 48.9%, Girls Schools 51.1% 2. In the past year, male students had more accidents(p〈.05) in school. 3. In examining students safety management control, 94.0% said that, there is an infirmary, there is a clear distinction between the playing fields and pathways(74.8%), and the chemicals in the labs are kept in a safe manner(77.2%). The above items were generally well maintained. However, the following recorded low scores. There are warning signs in hazardous places and facilities(30.5%), There is guiding principle to examine the safeness on a regular basis(24.9%), and There are slogans and posters preventing accidents(40.3%). 4. In examining the facilities of the schools that were surveyed, the majority answered, yes to the following. There are hazardous facilities or materials at school(62.9%), There are sharp edges in educational supplies and equipment(59.8%), There are nails or other components that are sticking out of desks and chairs(75.9%), There are slippery spots in the corridors and classrooms(69.3%), There are stones, scrap metal, broken glass, and trash on the playing fields(66.6%). Furthermore, the students surveyed said, yes to the following although in low percentages. The amount of sand on the playing fields is sufficient(49.1%), The soccer and basket goal posts are fastened (53.7%), There are safety bars on the windows of classrooms and corridors (27.4%), There are safety mats on the entrance to restrooms preventing slips (14.2%), The stairs have slip protection measures(49.1%). 5. In analyzing the affect that the school safety management system has on accidents in school, schools that had slogans and posters preventing accidents had a 50% less chance of accidents(p〈.05), schools with chemicals and equipment in the labs that were safely maintained had an 80% less probability of accidents(p〈.0l), and the schools that had sharp edges in the educational supplies and equipment had an 80% greater chance of accidents(p〈.01).

• Journal of the Korea Concrete Institute
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• v.17 no.2 s.86
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• pp.281-290
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• 2005

This paper presents experimental and analytical studies on long-term behavior of square CFT columns under central axial loading. Two loading cases are considered; (1) the load applied only at the inner concrete of the column and (2) the load applied simultaneously on both the concrete and the steel tube. Four specimens of square CFT columns were tested under the two loading cases, and basic creep test for two concrete specimens was performed to find out the creep properties of the inner concrete. Three-dimensional finite element analysis models were established and verified with the experimental results. The verification shows that the prediction for the long-term behavior of actual square CFT columns is possible from the three dimensional finite element modeling considering the bond behavior between steel tube and inner concrete. Also, experimental results and numerical calculations revealed that the bond stress Induced by the confinement pressure as well as the slip between inner concrete and steel tube were increased with time In the first loading case. However, the confinement by the loading Plate was decreased with time while increasing confinement effect by the steel tube was observed over time. In contrast no confinement effects occur in the second loading case.

• Journal of Adhesion and Interface
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• v.22 no.3
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• pp.85-90
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• 2021

Generally, the tensile strength of carbon fiber reinforced composite (CFRP) should be determined to produce this material. The tensile strength was performed based on ASTM D3039, and this test could cause the error by specimens and human. In this research, the CFRP tensile test was performed with different thickness of specimens and tap, adhesive for attaching tap, and pressure of jig to hold the specimens, while the test was performed based on ASTM D3039. The tensile stress and modulus exhibited differently with different specimen thicknesses, and the 1~1.5 mm thickness of the specimen was optimized. In the case of 0.28 MPa jig pressure, the slip or fracture at the clamping area of the specimen has not occurred, and specimens were fractured to the center section of the specimen. The adhesive to attach jig on specimen should be used to exhibit high adhesive stress. Experimental parameters could cause errors. It is expected to achieve an accurate tensile property evaluation of composite materials via improvements in adhesives, tabs, and jigs.

• Journal of the Society of Disaster Information
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• v.16 no.4
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• pp.796-805
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• 2020

Purpose: A static loading test was performed to evaluate the ultimate flexural strength of a girder in which 80MPa high-strength concrete was synthesized on the compressive flange of the I-shape steel girder. Method: This test is designed and fabricated two types of specimens with different shear-connection specifications, and evaluated their ultimate flexural behavior until reaching the extreme event limit states. In addition, the ultimate strength was evaluated by comparing the test results and the results of the strain compatibility method. Result: By confirming the displacement within 0.02mm as a result of the relative slip measurement, it was verified that the two specimens secured perfect bonding. Therefore, the difference in the shear specification does not have a great effect on the stiffness, and if the specimens are completely synthesized, there is no difference in the behavior until it reaches the extreme-event limit states. Conclusion: The girder to be tested has a working load within the elastic range and meets the usability requirements for allowable deflection. Therefore, even if a part of the casing is subjected to the tensile force at the level of cracking, the deck will first reach the compression failure due to the role of the reinforcing bar.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.3
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• pp.77-84
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• 2021

In this study, flexural tests of prestressed high strength spun concrete (PHC) piles reinforced with infilled concrete and longitudinal rebars were conducted, where the longitudinal rebar ratio and the presence of sludge formed on the inner surface of PHC pile were set as key test variables. A total of six PHC pile specimens were manufactured, and their flexural behaviors including failure mode, crack pattern, longitudinal strain distribution in a section and end slip between external PHC pile and infilled concrete were measured and discussed in detail. The test results revealed that the flexural stiffness and strength increased as the longitudinal rebar ratio became larger, and that the sludge formed on the inner surface of PHC pile did not show any detrimental effect on the flexural performance. In addition to the experimental approach, this study presents a nonlinear flexural analysis model considering compatibility conditions and strain and stress distributions of the PHC piles and infilled concrete. The rationality of the nonlinear flexural analysis model was verified by comparing it with test results, and it appeared that the proposed model well evaluated the flexural behavior of PHC piles reinforced with infilled concrete and longitudinal rebars with a good accuracy.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.3
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• pp.184-191
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• 2023

With increasing corrosion in RC (Reinforced Concrete) structures, cracks occurred due to corrosion products and bearing load resistance decreased. In this study, corrosion was induced through an accelerated corrosion test (ICM: Impressed Current Method) with 140 hours of duration, and changes in USV (Ultra-Sonic Velocity), flexural failure load, and corrosion weight were evaluated before and after corrosion test. Three levels of cover depth (20 mm, 30 mm, and 40 mm) were considered, and the initial cracking period increased and the rust around steel decreased with increasing cover depth. In addition, the USV linearly decreased with decreasing cover depth and increasing amount of corrosion. In the flexural loading test, the bending capacity decreased by more than 10% due to corrosion, but a clear correlation could not be obtained since the corrosion ratio was small, so that the effect of slip was greater than that of reduced cross-sectional area of steel due to corrosion. As cover depth increased, the produced corrosion amount and USV changed with a clear linear relationship, and the cracking period due to corrosion could be estimated by the gradient of the measured corrosion current.

• FLOWER RESEARCH JOURNAL
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• v.18 no.4
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• pp.238-243
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• 2010

This study was conducted to investigate effects of nutrient solution pH control agent and foliar spray of ethephon on the reduction of stem inside-cavity and improvement of flower quality in chrysanthemum 'Baekma'. Changes of pH in nutrient solution as affected by the kind of pH control agent showed more settled pattern in the plot of KOH treatment than in others. Plant growth and development such as cut flower length, leaf numbers, cut flower weight and petal number were the greatest in the plot of KOH. However, the size and area of stem cavity was large in KOH rather than $KHCO_3$. As changes in the absorbing patterns of mineral elements as affected by nutrient solution pH control agent in closed system, contents of total nitrate, phosphorus, potassium and calcium by $KHCO_3$ was absorbed into the plant less than KOH, so that it remained a lot of mineral element residues rather than KOH in closed system. Plant growth as affected by the foliar spray of ethephon showed growth retardation effect in the plot of solution diluted to 1 : 500 and growth promotion effect in the plot of solution diluted to 1 : 1,000 or 1 : 2,000. The number of petals was the best in the plot of foliar spray of ethephon solution diluted to 1 : 1,000 before flowering at 45 days showing 331 petals compared to control showing 302 petals. The size and area of stem cavity as affected the foliar spray of ethephon was smaller 1 mm and 7%, respectively, in the plot of solution diluted to 1 : 2,000 before flowering at 30 days than in control. Therefore, treating pH stabilization using KOH after floral initiation stage with the foliar spray of ethephon solution diluted to 1 : 2,000 before flowering at 30 days would help to reduce stem cavity size and improve flower quality in hydroponically grown chrysanthemum 'Baekma'.

• Journal of Korean Orthopaedic Sports Medicine
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• v.10 no.2
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• pp.94-99
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• 2011

Purpose: As the number of people enjoying skiing and snowboarding which are two popular winter sports has been increasing, wearing helmet during doing these sports has been needed for safety. The rates of head or face injury have decreased after using helmet. However the effect that wearing helmet has on cervical damage is not yet to be known. So through this research we intend to be helpful in developing effective program and safety equipment. Materials and Methods: During two seasons from December 2009 to march 2011, cased 658 cervical injuries within 14538 admittance in medical center of major resort due to skiing and snow-boarding injuries. For survey and research model, one year before the research year conducted a pilot study. Admittance were 432 male and 226 female, advanced 273 and 385 novice. We divided them into two groups depending on wearing helmet, measured cervical damage ratio and injury mechanism, and researched the severity of damage and diagnosed injury. Each group used SPSS 12.0 (SPSS Inc., Chicago, IL, USA) to process data statistically. Results: The number of patients was 312 in skier and 346 in snow boarder. Patients wearing helmet were 146 in skier and 127 in snow boarder. Classification of each injuries were confirmed as 292 cases of simple sprain, 359 bruising, 6 cervical fractures and 1 case of dislocation. Classification of injury mechanisms were 287 of human collision, 212 material collision, 108 of slip down by oneself, 39 of falling and 12 cases of etc. In cases wearing helmet ski 78/ snow board 70 were simple sprain, ski 64/ snowboard 68 were shown as bruising, ski 1/ snow board 2 had cervical fracture or dislocation. The ratio of cervical sprain increased in cases of wearing helmet compared to non-wearing cases and there was a statistical significance (p<0.001). The ratio of cervical contusion increased significantly in non-wearing helmet user (p<0.05). However, there was no significant increase in fracture and dislocation compared between helmet user and non-user (p> 0.05). Conclusion: In this study, wearing helmet had no relation to additional cervical injury occurrence or severity among skiers and snow boarders. The ratio of cervical sprain increased significantly in helmet user with person to person accident. However, the cervical contusion decreased. On this ground, further biomechanical studies are required and modified helmet will be necessary.