• Steel and Composite Structures
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• v.52 no.2
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• pp.121-134
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• 2024

To investigate the compressive behavior of partially encased recycled aggregate concrete (PERAC) stub columns after exposed to elevated temperatures, 22 specimens were tested. The maximum temperature suffered, the replacement ratio of recycled coarse aggregate (RCA), the endurance time and the spacing between links were considered as the main parameters. It was found that the failure mode of post-heated PERAC columns generally matched that of traditional partially encased composite (PEC) columns, but the flange of specimens appeared premature buckling after undergoing the temperature of 400℃ and above. Additionally, the ultimate strength and ductility of the specimens deteriorated with the elevated temperatures and extended heating time. When 400℃< T ≤ 600℃, the strength reduction range is the largest, about 11% ~ 17%. The higher the replacement ratio of RCA, the lower the ultimate strength of specimens. At the temperature of 600℃, the ultimate strength of specimens with the RCA replacement ratio of 50% and 100% is 0.94 and 0.91 times than that of specimens without RCA, respectively. But the specimen with 50% replacement ratio of RCA showed the best ductility performance. And the bearing capacity and ductility of PERAC stub columns were changed for the better due to the application of links. When the RCA replacement ratio is 100%, the ultimate strength of specimens with the link spacing of 100 mm and 50 mm increased 14% and 25% than that of the specimen without links, respectively. Based on the results above, a formula for calculating the ultimate strength of PERAC stub columns after exposure to high temperatures was proposed.

• Tribology and Lubricants
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• v.40 no.4
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• pp.133-138
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• 2024

This study evaluates the structural safety of wind turbine blades, analyzes the behavior of composite laminate structures with and without defects, and assesses surface erosion wear. The NREL 5 MW standard is applied to assign accurate composite material properties to each blade section. Modeling and analysis of the wind turbine blades reveal stable behavior under individual load conditions (gravity, motor speed, wind speed), with the web bearing most of the load. Surface erosion wear analysis in which microparticle impacts are simulated on the blade coating shows a maximum stress and maximum displacement of 14 MPa and 0.02 mm, respectively, indicating good initial durability, but suggest potential long-term performance issues due to cumulative effects. The study examines defect effects on composite laminate structures to compare the stress distribution, strain, and stiffness characteristics between normal and cracked states. Although normal conditions exhibit stable behavior, crack defects lead to fiber breakage, high-stress concentration in the vulnerable resin layer, and decreased rigidity. This demonstrates that local defects can compromise the safety of the entire structure. The study utilizes finite element analysis to simulate various load scenarios and defect conditions. Results show that even minor defects can significantly alter stress distributions and potentially lead to catastrophic failure if left unaddressed. These findings provide valuable insights for wind turbine blade safety evaluations, surface protection strategies, and composite structure health management. The methodology and results can inform the design improvements, maintenance strategies, and defect detection techniques of the wind energy industry.

• Journal of the Korean Geosynthetics Society
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• v.14 no.3
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• pp.31-42
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• 2015

The Reinforced subgrade for railroad (RSR) was constructed for one way railway line with the dimension of 5 m high, 6 m wide and 20 m long to evaluate its performance under train design load. The RSR has characteristics of short length (0.3-0.4 H) of reinforcement and rigid wall, 30 and 40 cm vertical spacing of reinforcement installation. To enhance economics and constructability, three kinds of connections (welding, hinge & bolt, bold wire) were also designed to realize the integration between rigid wall and reinforced subgrade. Two times of static loading tests were done on the full size railroad subgrade. The maximum applied pressure was 0.98 MPa (the maximum test load 5.88 MN), which corresponds to 19.6 times of the design load for railroad subgrade, 50 kPa. The performance on the RSR was evaluated with the safety on the failure, subgrade bearing capacity and settlement, horizontal displacement of wall, and reinforcement strain. Based on the full scale test, we confirmed that the RSR with the conditions of 0.35 H (35% of height) short reinforcement length, hinge & bolt type connection for integration between rigid wall and reinforced subgrade, and 40cm vertical spacing of reinforcement installment shows good performance under train design load.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.11
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• pp.144-150
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• 2019

In this study, resistance spot welding was performed using a high tensile steel plate SGAFC 780. The shear tensile strength, fracture profile, nugget diameter, and simulation were compared according to the conditions. After the nugget diameter calibration, the minimum diameter of welding was more than 4.3mm when the welding current was 8kVA or more. At 9kVA and above 10kVA, the minimum nugget diameter of 4.3mm was satisfied. On the other hand, due to the high current and time, the fly phenomenon occurred and the deep indentation remained. An evaluation of the weldability confirmed that there was an interval that was evaluated as weld failure due to the creep phenomenon, which satisfied the tensile shear strength and minimum nugget diameter. On the other hand, areas that have sufficient load bearing capacity even when drift has occurred were also identified. The simulation results show that the error rate was less than 4.2% when comparing the nugget diameter in the simulation and the experimental results in the appropriate weld zone, and confirmed the reliability of the simulation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.2
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• pp.143-154
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• 2016

This study investigated the occurrences, causes, and mitigation of the recent ground subsidence and underground cavity generation events in Korea. Two main causes of ground subsidence are (1) the soil erosion by seepage during tunneling and earth excavation and (2) the damage of underground pipes. The main cause of the soil erosion during tunneling was the uncontrolled groundwater flow. Especially, when excavating soft grounds using a tunnel boring machine (TBM), the ground near TBM operation halt points were found to be the most vulnerable to failure. The damage of underground pipes was mainly caused by poor construction, material deterioration, and differential settlement in soft soils. The ground subsidence during tunneling and earth excavation can be managed by monitoring the outflow of groundwater and eroded soils in construction sites. It is expected that the ground subsidence by the underground pipe damage can be managed or mitigated by life cycle analysis and maintenance of the buried pipes, and by controlling the earth pressure distribution or increasing the bearing capacity at the upper ground of the buried pipes.

• Journal of Korean Orthopaedic Sports Medicine
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• v.11 no.1
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• pp.37-43
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• 2012

Purpose: This study is to evaluate the clinical results of pull-out suture for root tear of posterior horn of medial meniscus. Materials and Methods: Between March 2006 and February 2011, We studied 40 cases with the root tear of posterior horn of medial meniscus which follow up more than 1 years. Mean age was 49.5 years old. We excluded osteoarthritis or varus deformity patients more than 5 degrees. pull-out suture was performed to the patients with grade 0-2 of Kellgren and Lawrence classification. According to Outerbridge classification, evaluation of cartilage damage was performed during arthroscopy. Evaluation of clinical result was used the Lysholm score. Results: The mean pre-operation Lysholm score was 63.9 and post-operation score was 86.3. The complete failure rate was 3 of 40 cases (7.5%). Twenty of 40 cases (50%) showed cartilage lesions in weight bearing portion of medial femoral condyle which were 12 cases in grade 1, 5 cases in grade 2 and 3 cases in grade 3 according to the Outerbridge classification. Conclusion: In the treatment of pull-out suture for root tear of posterior horn of medial meniscus, exclusion of more than moderate arthritis or varus deformity is very importment. Pull-out suture seems to be a useful treatment of the root tear of posterior horn of medial meniscus in mild osteoarthritis or varus deformity of middle ages.

• The Journal of Engineering Geology
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• v.14 no.4 s.41
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• pp.487-498
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• 2004

There is an increasing trend of construction works in mountainous areas by the urban development in Busan that is mainly composed of mountains. The study area, Hwangryeong Mt., is one of developing sites in the urban area, too. Landslides and cut-slope failures that occur large damages of human beings and the properties are influenced by soil characteristics as well as rock properties. This study analyzed geotechnical characteristics of soil dependent on geology at Hwangryeong Mt. where a large slope failure had been occurred in 1999. Geology of the study area is composed of the Cretaceous sedimentary rocks and volcanic rocks. Soil layer of the slopes can be grouped into sand mixed with clay and silt. The cohesion is plotted between $0.001\;and\;0.066kg/cm^2$. The friction angles are distributed in the ranges between $32^{\circ}\;and\;39^{\circ}$, meaning soil bearing a high friction angle. The permeability coefficients are plotted between $2.34\times10^{-4}cm/sec\;and\;2.58\times10^{-2}cm/sec$, indicating fine sand and loose silt with a medium grade of permeability. The sedimentary rocks area shows relatively higher permeability coefficients than those volcanic rocks area.

• Journal of Veterinary Clinics
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• v.30 no.5
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• pp.384-386
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• 2013

A two-year-old, female English bulldog was referred for breeding by artificial insemination with frozen semen of male English bulldog, a litter of female bulldog's grandfather. Intrauterine artificial insemination was done two days after the ovulation day. Sperm was evaluated after thawing by computer assisted sperm analyzer, and its motility was 89.8% with normal shape. Pregnancy bearing eight fetuses was diagnosed by ultrasonography and radiography. Cesarean section was performed sixty days after the artificial insemination. Eight pups were delivered with safe, but the entire pup had abnormalities including severe bow-legged malformations, cleft lip, cleft palate, and enlarged cranial part.

• Journal of the Korean GEO-environmental Society
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• v.15 no.9
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• pp.69-75
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• 2014

Rock fall protection system installed against rock slope is one of the most conventional way to protect nearby infra structures. Despite of wide application of typical rectangular nets, virtually installed to protect rock slope face, several problems have also been pointed out up to date. Rectangular draped nets are vulnerable to a sudden external shock such as rock fall, because it doesn't have any systematical buffers or shock absorbers. Furthermore, it has been widely recognized from the some cases of rock fall accident in Korea that rock fall protection nets cause wide range of failure in the rock slope faces due to insufficient pullout bearing capacity of fixing parts. Therefore, in this study, we tried to make a consideration about the problems of existing standard rock fall protection nets in Korea, and develop a new type of hexagonal net with a shock absorber based on design rock fall energy. In this paper, laboratory and full scale test procedure is described to analysis the performance of newly developed hexagonal rock fall net, and the key results are presented and discussed.

• Journal of the Korean Arthroscopy Society
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• v.9 no.1
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• pp.40-45
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• 2005

Purpose: This study is to evaluate the clinical findings of media] meniscus root tear, pull-out repair technique and it's short term results. Materials and Methods: From September 2003 to August 2004, 23 cases of total 27 medial meniscus root tears were treated by pull-out repair technique. Mean age was 60.2 years old. The pull-out technique was divided into 2 groups In group 1(14/23 cases), anterolateral portal was used and in group 2(9/23 cases), anterolateral and posteromedial portals were used for bed preparation. Concomitant cartilage lesions were documented as ICRS mapping system. The clinical outcomes were evaluated according to Lysholm Knee Score. Results: The postoperative Lysholm Knee Score was 77.1(range; $58{\sim}97$) in group 1 and 81.4(range; $72{\sim}94$) (p>0.05). The failure rate was 3 of 14 cases(21.4%) in group 1 and 1 of 9 cases(11.1%) in group 2. Twenty of 22 cases(90.9%) showed cartilage lesions in weight bearing portion of medial femoral condyle which were 8 grade III and 5 grade IV according to the Outerbridge classification. Conclusion: Pull-out repair seems to be a useful treatment of the medial meniscus root tear for preservation of circumferential hoop tension of meniscus.