• Advances in concrete construction
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• v.7 no.1
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• pp.1-9
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• 2019

The conventional ACI rectangular stress block is developed on the basis of normal-strength concrete column tests and it is still being used for the design of high-strength concrete members. Many research papers found in the literature indicate that the nominal strength of high-strength concrete members appears to be over-predicted by the ACI rectangular stress block. This is especially true for HSC columns. The general shape of the stress-strain curve of high-strength concrete becomes more likely as a triangle. A triangular stress block is, therefore, introduced in this paper. The proposed stress block is verified using a database which consists of 52 tested singly reinforced high-strength concrete beams having concrete strength above 55 MPa (8,000 psi). In addition, the proposed model is compared with models of various design codes and proposals of researchers found in the literature. The nominal flexural strengths computed using the proposed stress block are in a good agreement with the tested data as well as with that obtained from design codes models and proposals of researchers.

• Journal of the Korean Society of Clothing and Textiles
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• v.25 no.3
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• pp.617-628
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• 2001

Cotton and silk fabrics dyed with brazilein(Caesalpinia Sappan), berberine (Phellodendron Amurense), and shikonin(Lithospermum Erythrorhizon) were stored in the air, in the water, and under the ground for about one year. The change of the color, the flexibility, and the breaking strength were measured at the intervals of few weeks. The results are as follows; 1. The color of the fabrics changed most extensively in the fabrics that were under the ground, then in the order of the ones that were in the water, and in the air. The color of the fabrics changed to the achromatic color over the time. 2. The flexibility change among the dyes was similar. All the fabrics became stiff under the ground and in the water over the storage time. 3. In general, cotton and silk fabrics dyed with berberine showed better strength retention than the fabrics dyed with other substances. 4. The strength retention of cotton fabrics was high in the order of the fabrics which were in the air, in the water, and under the ground. Only minuscule change occurred in the strength of the cotton fabrics. The strength of the fabrics that were in the water and under the ground decreased remarkably after 30 weeks and 20 weeks respectively. 5. The strength retention of silk fabrics was high in the order of the fabrics which were in the air, under the ground, and in the water. In the air, the strength on silk fabrics decreased rapidly after 30 weeks. In the water, the strength of silk fabrics decreased more rapidly than that of the cotton fabrics. Under the ground, the strength retention of silk was higher than that of cotton.

• Journal of Korean Academy of Nursing
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• v.23 no.1
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• pp.56-67
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• 1993

The purpose of this study was to compare the circumference and skinfold thickness of upper and lower limb and the leg strength of the casted limb with those of the normal limb after removal of a leg cast. The subjects for the study were orthopedic patients who had had long and short leg casts or splints due to tibial, fibulal, metatarsal, calcaneus fracture or ankle sprains. The subjects were divided into two groups, those who had the cast on for less than 40 days and those for over 41 days. Circumference and skinfold thickness of the upper and lower limb on the side on which the cast was ap-plied were compared with those of the contralateral side after removal of the cast. Circumference and skinfold thickness of the upper and lower limb, and leg strength for those in a cast for under 40 days were compared with those of over 41 days for both the side to which cast was applied and the contralateral side. Measurements were made after removal of the cast. Skinfold thickness was measured by fat caliper, circumference was measured by tape and lower extremity strength was determined with flat foot pressing on an electronic digital health meter in the sitting position. The results can be summarized as follows : 1. The circumference of the upper and lower leg on the side on which the cast was applied, when measured after the cast was removed, were significantly less than those of the normal side, 93.88%, 93.11% each. 2. Skinfold thickness of the quadriceps and gastrocnemius on the side on which the cast was applied were significantly less than those of the normal side when measured after removal of the cast, 85.98%, 82.85% respectively. 3. Leg strength on the side where the cast was applied was significantly 1ss than that on the normal side, 60.20%. 4. There was no difference in the circumference of upper and lower limbs, skinfold thickness or leg strength on the side where the cast was applied between the group which had the cast applied for under 40 days and the group that had it applied for over 41 days. 5. The circumference of the upper arm and lower leg on the normal side for the group that had the cast applied for over 41 days was significantly greater than the group that had the cast application for under 40 days. T ere was no difference between the two groups in the circumference of the forearm and upper leg, skinfold thickness and leg strength in the normal side. From these results, it may be concluded that muscle atrophy was apparent in the casted limb compared to the normal limb, and the circumference of the upper arm and lower leg, and leg strength on the normal side increased after removal of the cast in the group which had the cast on for more than 41 days.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.11a
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• pp.53-54
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• 2015

As the result of uniaxial compression strength test on the CLMS mixing BFS and SS with BFS 4000, it required to determine the desired strength through increasing unit quantity of cement in mixing process because of dramatic strength deterioration of strength according to increasing replacing rate. In this study's result, regardless of differences in fine aggregates used, in order to get uniaxial compression strength in the scope exceeding criteria of minimum strength for applying to the field, the most reasonable combination was to mix replacing BFS with fineness of 6000 in 30%. For the CLMS mixing BFS and SS, in order to improve flow ability by securing quantity of minimum unit and to repress bleeding rate with securing uniaxial compress strength considering the field applicability, regardless of differences in fine aggregates used, to mix BFS over 6000 in 30% was most effective.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.5-8
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• 2005

The purpose of this study is to investigate the mechanical characteristics of plain and steel fiber high strength concrete under uniaxial and biaxial loading condition. A number of plain and steel fiber high strength concrete cubes having 28 days compressive strength of 82.7Mpa (12,000psi) were made and tested. Four principal compression stress ratios, and four fiber concentrations were selected as major test variables. From test results, it is shown that confinement stress in minor stress direction has pronounced effect on the strength and deformational behavior. Both of the stiffness and ultimate strength of the plain and fiber high strength concrete increased. The maximum increase of ultimate strength occurred at biaxial stress ratio of 0.5 in the plain high strength concrete and the value were recorded 30 percent over than the strength under uniaxial condition. The failure modes of plain high strength concrete under uniaxial compression were shown as splitting type of failure but steel fiber concrete specimens under biaxial condition showed shear type failure.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.395-398
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• 2005

In recent years, the applications of high-strength concrete have increased, and high-strength concrete has now been used in many parts of the world. The growth has been possible as a. result of recent developments in material technology and a demand for higher-strength concrete in Korea. In this study, we have an object to produce the ultra-high strength concrete(Super-Con) of over 100MPa with low price materials. First, the binders for Super-Con should be selected by the tests; setting time of paste, flow value and strength of mortar. From the test results, the binders are blended with ordinary portland cement, pulverized portland cement and silica fume. Fundamentally the compressive strength, frost resistance and chloride resistance are investigated.

• Journal of the Korea Concrete Institute
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• v.29 no.2
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• pp.141-148
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• 2017

This study is experimentally investigated the effects of various steam curing parameters on the early-age compressive strength development of high strength concrete (over 40 MPa) in the precast plant production. High strength concrete are used only ordinary portland cement (type I) and water-cement ratio selected 3cases (25%, 35% and 45%). Also, steam curing parameters are as followings ; (1) Preset period 2cases (3 hours and 6 hours) (2) Maximum curing temperature 3cases ($45^{\circ}C$, $55^{\circ}C$ and $65^{\circ}C$) (3) Maintenance time of curing temperature 3cases (4 hours, 6 hours and 8 hours) (4) Maximum rate of heating and cooling $15^{\circ}C$/hr. Initial setting time and adiabatic temperature rising ratio of these concrete according to water-cement ratio are tested before main tests and examined the compressive strength development for the steam curing parameters. Also compressive strength are compared with optimum steam curing condition and standard curing at test ages. As test results, the optimum steam curing conditions for high strength concrete(over 40 MPa) are as followings. (1) Preset period ; over initial setting time of concrete (2) Maximum curing temperature ; bellow $55^{\circ}C$ (3) Maintenance time of curing temperature ; bellow 6hours. Also strength development of steam curing concrete show in the reversed strength at 28 days. It is to propose an efficient steam curing condition for high strength concrete in the precast method.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.10a
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• pp.243-249
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• 1993

The porpose of this study is to suggest an experimental for shear wall of reinforced concrete wall structure. A series of experimental be performed for earned to strength and deformation property of reinforced concrete shear wall. These specimens are three R/C walls among five models which had boundary. As a result, it was found that cyclic experiment is very proper and cyclic time must be increased 3 or 5 times. Monotonic test results was indicated over 15% than other experiment for yielding strength and ultimate strength.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.10a
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• pp.250-255
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• 1993

This research is aimed at the experimental investigation of the characteristic contribution of the structural parameters, such as concrete over, concrete strength and reinforcing bar size on the dowel strength of the reinforced concrete stuctures. A total of twenty four specimens were tested for eight experimental conditions. The test results showed relatively close agreements with the values calculated by Vintzeleou-tassios equation. From the observations of the test results, it was found that the concrete cover affected almost linearly on the dowel strength , while the var size and the concrete strength showed coupled effects.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.148-152
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• 2000

The experimental study was performed to investigate the effects of centrifugal condition on the segregated layers of materials and the compressive strength of concrete for pretensioned spun high strength concrete (PHC) pile. The considering factors in the test were the centrifugal time and the magnitude of centrifugal force. These factors have been found to have found to have the great influence on the segregation and the concrete strength. The moderate centrifugal condition has to be fitted for the quality assurance in the production of PHC pile, especially to provide the adequate concrete cover over the tendons.