• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.555-560
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• 2003

Fatigue strength of concrete is ususlly presented by the Wohler Curve. But, new dimension T(time) from the view point of cyclic creep concept should be considerd. This paper presented four variable F-N-T-R relationship, this four variable relationship simultaneously accounts for the time effect and the effect of load rate. And analytical models are presented to predict fatigue strength of R/C beam strengthened with steel plate and carbon fiber sheet. Also, the correlation between the ratio of stress and the fatigue life was investigated.

• KCI Concrete Journal
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• v.14 no.2
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• pp.81-85
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• 2002

The strength development of concrete is influenced by temperature and cement type which greatly affect hydration degree of cement. There is not pertinent concrete strength management method in korea. There are several methods for estimating the in-place strength of concrete. One such method is the maturity concept. The maturity concept is based on the fact that concrete gains strength gradually as a result of chemical reactions between cement and water; and for a specific concrete mixture, strength at any age and at normal conditions is related to the degree of hydration. The rate of hydration and, therefore, strength development of a given concrete will be a function of its temperature. Thus, strength of concrete depends on its time-temperature history. The goals of the present study are to investigate a relationship between strength of high-strength concrete and maturity that is expressed as a function of an integral of the curing period and temperature and predict strength of concrete.

• Journal of Nutrition and Health
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• v.33 no.3
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• pp.279-288
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• 2000

The study examined BMIs, physical strength, activities, and the attitudes and behavior toward weight control among 7,968 Korean students{2,435 5th graders from elementary schools(ESs), 2,524 2nd graders from middle schools(MSs), 2,739 2nd graders from high schools(HSs)} nationwide. Compared to the 1987 data, there were increases of height(3-6cm) and weight(3-8kg), but decreases of physical strength and exercise. Lack of 'regular exercise' among girls from MSs and HSs and higher proportion of time spent on watching TV and using a computer for elementary schoolers were particularly noticeable. Proportions of students who were satisfied with their body weight were 49% for ESs, 35% for MSs, and 29% for HSs. There was no relationship between subjective and objective evaluations of body weight. Diet rather than exercise was more frequently chosen as a method of weight control. Compared to boys, girls showed stronger association between the amount of exercise and the subjective body weight in MSs and HSs, however this association was not found for the subjects from HSs. Values for the 50th percentile of BMI of boys and girls were 18.4 and 17.7 for ESs, 19.9 and 20.1for MSs, and 21.4 and 20.6 for HSs. In MSs and HSs, boys with BMI between 15th to 85th percentiles were physically stronger than those whose BMIs were lower than 15th kor higher than 85th percentiles. For the other groups, there was a trend of a positive relationship between BMI and physical strength. Based on the analyses of BMI and physical strength, this study suggests 22 and 21 for upper grades in ESs, 24 and 23 for MSs, and 27 and 25 for HSs as the respective cut off points of BMI for weight control n boys and girls. A need for implementing nutrition education program focused on weight control is also suggested.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.6
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• pp.2664-2671
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• 2012

This study aimed to investigate the relationship between physical characteristics and walking ability in the elderly population. Subjects were 77 elderly (38 men and 39 women) who are capable of walking independently with and without walking aids. Correlation and stepwise multiple linear regression analyses were used to analyze the relationship between physical characteristics (age, gender, height, weight, body mass index, muscle mass, waist/hip ratio, heart rate, vital capacity, flexibility, maximum oxygen consumption, one-leg standing time, and strength of knee flexor and extensor) and walking velocity of subjects. Age, height, vital capacity, one-leg standing time, and strength of knee flexor and extensor showed significant correlations with walking velocity of subjects (p<.05). Further, the strength of knee flexor explained 27% of the variance, and up to 32% of the walking velocity could be explained when the strength of knee extensor were added to the model. The findings suggest that walking velocity of elderly depends on the strength of lower limb's strength and a variety of physical characteristics.

• Advances in concrete construction
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• v.9 no.4
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• pp.413-421
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• 2020

For steel-concrete girders made composite using shear studs, initial damage on studs induced by weld defect, unexpected overloading, fatigue and others might degrade the service performance and even threaten the structural safety. This paper conducted a numerical study to investigate the static behavior of damaged stud shear connectors that were embedded in ultra high performance concrete (UHPC). Parameters included damage degree and damage location. The material nonlinear behavior was characterized by multi-linear stress-strain relationship and damage plasticity model. The results indicated that the shear strength was not sensitive to the damage degree when the damage occurred at 2/3d (d is the stud diameter) from the stud root. An increased stud area would be engaged in resisting shear force as the distance of damage location from stud root increased and the failure section becomes inclined, resulting in a less reduction in the shear strength and shear stiffness. The reduction factor was proposed to consider the degradation of the shear strength of the damaged stud. The reduction factor can be calculated using two approaches: a linear relationship and a square relationship with the damage degree corresponding to the shear strength dominated by the section area and the nominal diameter of the damaged stud. It was found that the proposed method is preferred to predict the shear strength of a stud with initial damage.

• Journal of the Korean Geotechnical Society
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• v.36 no.7
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• pp.29-40
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• 2020

In this study, various laboratory tests were conducted to evaluate the effect of the moisture conditions of Jeju basalt on the mechanical properties. Twenty specimens were produced respectively from basalts collected from Sangga-ri and Eoeum-ri in northwestern Jeju. The tests were performed under saturated and dry conditions, and the results of these tests were used to examine the relationship with the physical properties and the mechanical properties depending on the moisture conditions. As a result of analysis with the test results and references, it was found that the uniaxial compressive strength, Brazilian tensile strength and elastic modulus in the saturated condition decrease at a similar ratio as compared with the dry condition. Also, the Brazilian tensile strength and the uniaxial compressive strength were in a linear proportional relationship, and in the moisture conditions, this relationship was not significantly affected.

• Structural Engineering and Mechanics
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• v.11 no.3
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• pp.301-314
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• 2001

The purpose of this experimental study is to investigate the damage mechanism due to shear-fatigue behavior of high-strength reinforced concrete beams under repeated loading. The relationship between the number of cycles and the deflection or strain, the crack growths and modes of failure with the increase of number of cycles, fatigue strength, and S-N curve were observed through a fatigue test. Based on the fatigue test results, high-strength reinforced concrete beams failed at 57-66 percent of static ultimate strength for 2 million cycles. The fatigue strength at 2 million cycles from S-N curves was shown as about 60 percent of static ultimate strength. Compared to normal-strength reinforced concrete beams, fatigue capacity of high-strength reinforced concrete beams was similar to or lower than fatigue capacity of normal-strength reinforced concrete beams. Fatigue capacity of normal-strength reinforced concrete beams improved by over 60 percent.

• Journal of Korean Academy of Fundamentals of Nursing
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• v.10 no.1
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• pp.30-36
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• 2003

Purpose: The strength of hand grip, low back muscles and knee joint muscles were measured and then compared to the bone mineral density (BMD) of each forearm bones (including ulna and radius), lumbar spine, and femur in young women in order to identify the relationship between muscle strength and bone mineral density. Method: The BMD was measured with a Dual Energy X-ray Absorptiometry and muscle strength was measured with a handgrip dynamometer and a Cybex Norm. Data were analyzed with frequencies, percentages, means, and Pearson correlation coefficients. Result: 1) Higher grip strength correlated positively with higher BMD in the forearm (r=.246, p=.007), higher low back extensor strength with higher BMD in the femur (neck, trochanter and Ward's triangle)($r=.323{\sim}.226$, $p=.003{\sim}.043$) and higher strength in the knee joint extensor with higher BMD in the lumbar spine (r=.227, p=.041), femur neck, and femur trochanter significantly ($r=.295{\sim}.226$, $p=.007{\sim}.043$). There was no significant correlation between the strength of low back extensors and BMD in the lumbar spine, now with strength of knee joint flexor and the BMD in the femur. 2) The muscle strength of each part of the body had significant positive correlations to each other part ($r=.255{\sim}.728$ $p=.021{\sim}.000$) Conclusion: The results of this study showed that with the development of a muscle there was an increased BMD of the corresponding part, and the BMD of each part was influenced by adjacent muscles. To promote the health of bones, it is important to strengthen the muscles of related bones, based on balanced development of all muscles.

• International Journal of Highway Engineering
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• v.19 no.2
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• pp.87-95
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• 2017

PURPOSES : The objectives of this study are to evaluate moisture sensitivity of various asphalt mixtures and to suggest an alternate method for the dynamic immersion test, which is used to determine the application of anti-stripping agent, by analyzing bond strength. METHODS : The bond strength of various asphalt mixtures such as hot mix asphalt, warm mix asphalt, and polymer-modified asphalt was evaluated by the ABS test. In order to characterize moisture sensitivity at different temperatures of the mixtures, the ABS test was conducted at $-10^{\circ}C$, $5^{\circ}C$, $20^{\circ}C$, $40^{\circ}C$, and $54^{\circ}C$ under both dry and wet conditions. The concept of the bond strength ratio was applied for objective moisture sensitivity analysis. Moreover, the bond strength characteristic was compared to the dynamic immersion test to suggest an alternate method to determine the application of anti-stripping agent. RESULTS AND CONCLUSIONS : Overall, the polymer-modified asphalt demonstrates the highest bond strength characteristic regardless of moisture condition and temperature. The bond strength characteristic displays a highly reliable linear relationship from $5^{\circ}C$ to $40^{\circ}C$, and the relationship could be used to predict bond strength at any intermediate temperature. Based on the analysis of bond strength and retained asphalt ratio, the bond strength value of 1254 kPa could be applied as a criterion for anti-stripping agent.

• Journal of International Academy of Physical Therapy Research
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• v.9 no.1
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• pp.1426-1434
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• 2018

This study was conducted to observe the isokinetic strength (IS) of the hip, ankle, and knee joints in young age groups. Thirty eight men and thirty one women with mean age of $30.4{\pm}3.5$ and $32.8{\pm}4.4years$, respectively, were enrolled in this study. Measurements of hip flexion, extension, abduction, and adduction at $30^{\circ}/sec$, Knee flexion and extension at $60^{\circ}/sec$, ankle inversion, eversion, plantarflexion, and dorsiflexion $30^{\circ}/sec$ were conducted. Absolute IS (Nm), relative IS (Nm/kg), strength ratios, correlations between movements were observed. Significant differences in absolute and relative strength were observed between groups in all movement except in the relative ankle strength. Relative isokinetic strength ratios of hip flexion/extension were .45 and .55, knee flexion/extension were .84 and .89, ankle dorsi/plantarflexion were .30 and .29, and ankle eversion/inversion were .86 and .84 for men and women, respectively. In the hip extension, men had about three times the body weight, and women had about 2.5 times the strength. The abduction muscle had about 1.5 times the body weight of both men and women. Height and body weight showed the significantly strong correlating relationship with hip (r, .76-.86) and knee (r, .67-.84) strength. However, ankle strength showed the comparatively correlating relationship, especially in women (r, .03 - .36). Similar age and physique characteristics of female and male groups could provide useful isokinetic strength reference values for developing the exercise program for healthy and rehabilitation groups.