• Steel and Composite Structures
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• v.33 no.3
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• pp.433-444
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• 2019

Fatigue failure of a grid structure using bolt-sphere joints is liable to occur in a high-strength bolt due to the alternating and reciprocal actions of a suspension crane. In this study, variable amplitude fatigue tests were carried out on 20 40 Cr steel alloy M30 high-strength bolts using an MTS fatigue testing machine, and four cyclic stress amplitude loading patterns, Low-High, High-Low, Low-High-Low, and High-Low-High, were tested. The scanning electron microscope images of bolt fatigue failure due to variable amplitude stress were obtained, and the fractographic analysis of fatigue fractures was performed to investigate the fatigue failure mechanisms. Based on the available data from the constant amplitude fatigue tests, the variable amplitude fatigue life of an M30 high-strength bolt in a bolt-sphere joint was estimated using both Miner's rule and the Corten-Dolan model. Since both cumulative damage models gave similar predictions, Miner's rule is suggested for estimating the variable-amplitude fatigue life of M30 high-strength bolts in a grid structure with bolt-sphere joints; the S-N fatigue curve of the M30 high-strength bolts under variable amplitude loading was derived using equivalent stress amplitude as a design parameter.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.353-356
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• 2005

Strength development of low heat portland cement(Type IV) concrete in high strength range is tested. In this study strength development according to water-binder ratio, strength development according to age, effect of fly ash and super plasticizer are tested. This study tests effect of low heat portland cement in high strength range concrete and provide guide line concrete mix design for later study and/or construction.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2012.11a
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• pp.77-79
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• 2012

This paper intends to review possible application in the high strength area through compressive strength estimation of the simulated high strength concrete member using Rock Test Hammer and suggest it as a reference data for the strength estimation technique of the ultra high strength concrete in the future. From the results of our test, in the low strength area less than 15MPa and normal strength area in 15~60MPa, as shown on the existing studies, it is indicated that P Type Schmidt Hammer in the low strength area and N Type Schmidt Hammer in the normal strength area have high correlation of rebound-compressive strength. As the Rock Test Hammer indicated more or less reduced accuracy in the low strength area and the normal strength area but high correlation on the high strength area (50~100MPa) defined on this test, it is determined that it would be possible to make the fastest and simplest compressive strength estimation on the site where the high strength concrete is applied.

• Computers and Concrete
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• v.5 no.5
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• pp.491-501
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• 2008

The present study verifies compressive strength, ultrasonic pulse velocity, electrical resistance,permeable ratio, and shrinkage from waste glass controlled low strength materials (WGCLSM) and early-high-strength WGCSLM specimens, by replacing the sand with waste glass percentages of 0%, 10%,20%, and 30%. This study reveals that increasing amounts of waste LCD glass incorporated into concrete increases WGCLSM fluidity and reduces the setting time, resulting in good working properties. By increasing the glass to sand replacement ratio, the compressive strength decreases to achieve low-strength effects. Furthermore, the electrical resistance also rises as a result of increasing the glass to sand replacement ratio. Early-high-strength WGCSLM aged 28 days has twice the electrical resistance compared to general WGCSLM. Early-high-strength WGCSLM aged 7 days has a higher ultrasonic pulse velocity similar to WGCSLM aged 28 days. The variation of length with age of different compositions is all within the tolerance range of 0.025%. This study demonstrates that the proper composition ratio of waste LCD glass to sand in early-high-strength WGCSLM can be determined by using different amounts of glass-sand. A mechanism for LCD optical waste glass usage can be established to achieve industrial waste minimization, resource recycling, and economic security.

• Physical Therapy Korea
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• v.24 no.1
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• pp.79-85
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• 2017

Background: The wall squat is considered an effective exercise because it can reduce the knee load and prevent excessive lumbar movement. However, the relationship between wall squat performance and strength of knee extensors and hip extensors remained unclear. Objects: The purpose of this study was to compare the strengths of the knee extensors and hip extensors between groups with low and high wall squat performance. Method: Nineteen males (low performance group: 9 subjects, high performance group: 10 subjects) participated in this study and performed wall squats. The subjects who were performing less than 30% of the average wall squat count were classified into the low wall squat performance group (less than or equal to 4 times) and the subjects who performed more than 30% of the average wall squat count were classified into the high wall squat performance group (greater than or equal to 8 times). Knee extensor and hip extensor strength were measured with a strength measurement system. An independent t-test was used to compare the strengths of the knee extensors and hip extensors between the groups with low and high wall squat performance. Results: The ratios of knee extensor and hip extensor strength to bodyweight were greater in the high wall squat performance group than in the low wall squat performance group (knee extensors: p<.001; hip extensors: p=.03). In the high- and low-performance groups, the ratios of knee extensor strength to bodyweight were $42.74{\pm}5.72$ and $30.76{\pm}8.54$, respectively, and the ratios of hip extensor strength to bodyweight were $31.95{\pm}10.61$ and $20.66{\pm}11.25$, respectively. Conclusion: Our findings suggest that knee extensor and hip extensor strength are needed for high wall squat performance. Thus, exercise to increase the knee and hip extensors strength can be recommended to improve squat performance.

• Proceedings of the Korea Concrete Institute Conference
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• 1991.10a
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• pp.140-145
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• 1991

Tests were conducted to get a mix proportioning of high strength concrete between σ28 and (C/W) using low quality materials easily purchased in situ. Superplasticizer was used as a chemical admixture to compensate low slump of base concrete keeping it up about 15±2㎝. General material properties such as modulus of elasticity, poisson's ratio, unit weight and stress-strain characteristic of high strength concrete were obtained. Test results show that mix proportioning of high strength concrete proposed in this paper have reasonable validity and these can be used as a design criteria in high strength concrete construction.

• Journal of the Korean Society of Food Science and Nutrition
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• v.23 no.5
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• pp.827-831
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• 1994

Investigation on the extractability, Mg2+-, Ca2+ , EDTA-ATPase activity and solubility of actomyosin prepared from leg and breast muscle of silky fowol were as follows. The extractability of actomyosin in leg and breast muscle was 779mg/100g and 1, 318mg/100g respectively, breast muscle was higher than leg muscle . Mg2+-ATPase activity of actomyosin was high inionic strength 0.02-0.10 and Mg2+ATPase activity of low ionic strength was higher than high ionic strength not related to the part. Ca2+ ATPase activity was high in ionic strength 0.05-0.13, the activity of leg muscle was higher that breast muscle. And EDTA-ATPase activity showed low in low ionic strength and showed high in high ionic strength, and increased greatly depend ionic strength up to 0.4. The solubility of actomyosin was not different in leg and breast muscle , the solution started in KCI concentration of 0.3M and ended in DCI concentration of 0.4M.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.1
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• pp.27-32
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• 2014

This study analyzed the fundamental characteristics of concrete according to a ternary system mixing in order to reduce hydration heat of mass concrete and to improve early age strength. The results are as follows. The fluidity of unconsolidated concrete satisfied the target scope regardless of the binder conditions. When the replacement ratio between FA and BS increased, the slump of low heat-A mix and low heat-B mix increased, and air content was not affected by the change of binders. As for setting time, low heat cement mix had the fastest regardless of W/B, and high early strength low heat mix achieved 6 hours' reduction compared with low heat-B mix at initial set, and 12 hours' reduction at the final set respectively. As for the simple hydration heat, the low mix peak temperature was the highest and low heat-B mix had the lowest temperature. And high early strength low heat mix was similar with that of low heat-B. The compressive strength of hardened concrete had similar strength scope in all mixes except for low heat-B mix at early ages, and had unexceptionally similar one without huge differences at long-term ages.

• Journal of Families and Better Life
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• v.27 no.5
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• pp.123-135
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• 2009

The purpose of this study was to investigate the effects of family conflict and self-control on school maladjustments of early adolescents. Subjects of this study consisted 662 middle school students drawn from 4 middle schools in Cheong-ju city. The results of this study were as follows: First, younger students' maladjustment to teachers was influenced by variables such as school year, economic levels, conflict strength between parents, conflict settlement between parents, reliability between parents and children, communication between parents and children and self-control, etc. In other words, students' maladjustment to teachers was high at the students in the 2nd year rather than in the 1st year, low economic level, high conflict strength between parents that younger students perceived, low conflict settlement between parents, low reliability between parents and children, high hostility between parents and children and low self-control. Second, younger students' maladjustment to the class was influenced by variables such as gender, school year, economic levels, conflict strength between parents, reliability between parents and children, communication between parents and children, and self-control, etc. In other words, young students' maladjustment to the class was high at the 2nd year students rather than at the 1st year students, low economic level, high conflict strength between parents, low reliability between parents and children, poor communication between parents and children, and low self-control. Third, younger students' maladjustment to rules was influenced by variables such as school year, economic level, conflict level between parents, hostility between parents and children, and self-control, etc. In other words, younger students' maladjustment to rules was high at the 1st year students rather than the 2nd year students of middle school, low economic level, high conflict strength between parents, high hospitality between parents and children and low self-control, etc. Fourth, younger students' maladjustment to friends was influenced by variables such as conflict strength between parents, conflict settlement between parents, hospitality between parents and children, and self-control, etc. In other words, younger students' maladjustment to friends was high at high conflict strength between parents, low conflict settlement between parents, high hospitality between parents and children and low self-control, etc. In the study, self-control was found to be the most important variable at younger students' maladjustment to teachers, class and rules, etc, and conflict settlement between parents was found to be the most significant variable at younger students' maladjustment to friends.

• Korean Journal of Materials Research
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• v.24 no.10
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• pp.520-525
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• 2014

Effects of Cu and B on effective grain size and low-temperature toughness of thermo-mechanically processed high-strength bainitic steels were investigated in this study. The microstructure of the steel specimens was analyzed using optical, scanning, and transmission electron microscopy; their effective grain size was also characterized by electron back-scattered diffraction. To evaluate the strength and low-temperature toughness, tensile and Charpy impact tests were carried out. The specimens were composed of various low-temperature transformation products such as granular bainite (GB), degenerated upper bainite (DUB), lower bainite (LB), and lath marteniste (LM), dependent on the addition of Cu and B. The addition of Cu slightly increased the yield and tensile strength, but substantially deteriorated the low-temperature toughness because of the higher volume fraction of DUB with a large effective grain size. The specimen containing both Cu and B had the highest strength, but showed worse low-temperature toughness of higher ductile-brittle transition temperature (DBTT) and lower absorbed energy because it mostly consisted of LB and LM. In the B-added specimen, on the other hand, it was possible to obtain the best combination of high strength and good low-temperature toughness by decreasing the overall effective grain size via the appropriate formation of different low-temperature transformation products containing GB, DUB, and LB/LM.