• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.253-258
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• 2002

An evaluation equation of the minimum shear reinforcement content for reinforced concrete beams was theoretically proposed. The proposed equation takes into account the effects of compressive strength of concrete, longitudinal reinforcement content and shear span ratio. The proposed equation was compared with the current ACI 318-99 and CSA A23.3-94 codes.

• International Journal of Concrete Structures and Materials
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• v.5 no.1
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• pp.35-42
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• 2011

In this paper, a design equation for the punching shear capacity of steel fiber reinforced concrete (SFRC) slabs is proposed based on the Japan Society of Civil Engineers (JSCE) standard specifications. Addition of steel fibers into concrete improves mechanical behavior, ductility, and fatigue strength of concrete. Previous studies have demonstrated the effectiveness of fiber reinforcement in improving the shear behavior of reinforced concrete slabs. In this study, twelve SFRC slabs using hooked-ends type steel fibers are tested with varying fiber dosage, slab thickness, steel reinforcement ratio, and compressive strength. Furthermore, test data conducted by earlier researchers are involved to verify the proposed design equation. The proposed design equation addresses the fiber pull-out strength and the critical shear perimeter changed by the fiber factor. Consequently, it is confirmed that the proposed design equation can predict the punching shear capacity of SFRC slabs with an applicable accuracy.

• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.4
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• pp.91-98
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• 2002

Prediction for the compressive strength of concrete by non-destructive tests(NDT) has a tendency to show different outcomes according to various aggregates. The purpose of this study is to develop estimation equation by rebound number, ultrasonic velocity and combined method at concrete structures which used granite as coarse aggregates. The test variable is water/cement ratio(41.1%, 48.6%, 67.6%), curing method(moisture condition, dry condition) and age(7, 14, 28, 56). According to the test variable, new equation was suggested, and compared with the existing equations.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.381-384
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• 2002

This study aims to propose the new strength equation of concrete by penetration test. There are not only few estimate strength equation of concrete, but also many problems to apply them to the real structure because of speed, cost, easiness, structual damage, reliability and so on. For this study, there performed a series of test and proposed a strength equation as follows ; fc = 5661 - 219.5d ＋ $2.17d^2 (단, R^2 = 98.6%$) fc : estimated compressive strength of concrete by kgf/$cm^2$ d: penetrated depth of concrete by mm.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.10a
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• pp.245-250
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• 1996

The aim of this study is to suggest the new elastic modulus equation that suits to a domestic situation to coincide the improved mechanical properties of high-strength concrete and ultra-high-strength concrete. For thish purpose, this study collected the laboratory data more than 400 connceted with the the modulus of elasticity that performed in this country and also analyzed it statistically. The compressive strength of investigated concrete ranged from 400 to 1,400kg/$\textrm{cm}^2$. As a result, a practical and useful elastic modulus equation is proposed, it can be considered as most suitable equation in domestic situation.

• Magazine of the Korea Concrete Institute
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• v.8 no.6
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• pp.213-222
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• 1996

This paper presents the improved elastic modulus equation more appropriate to predict the modulus of elasticity of structural elements designed and made by high- and ultra high-strength concrete under domestic situation in Korea. To justify and assess the proposed elastic modulus equation, more than 400 laboratory test data domestically available in the literature and having the range of 400 to 1.000kg/$\textrm{cm}^2$ in concrete compressive strength were collected and analyzed statistically. Comparison of the proposed elastic modulus equation with the previously suggested equations in the ACI363R. CEB-FIP, NS3473 and New-RC were also presented to demonstrate the applicability to practice.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.1
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• pp.19-28
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• 2018

The time for form removal is an important factor for ensuring the safety and economical efficiency of concrete structures, because it affects the quality, period, and cost of construction. Although local specifications suggest the form curing time, there is a problem of low quality of concrete due to early removing of form. This is because they do not fully understand effect of curing condition, and they want to shorten construction period in the field. Therefore, this research evaluates the effect of curing condition according to the time for form removal by testing specimen. As a result, the concrete compressive strength at the age of 28 days decreased about 40% in the condition of form removal after 12 hours, while the strength in the condition of form removal after 28 days decreased about 7%. Finally, this paper suggests an estimating equation for the concrete compressive strength due to the time for form removal considering various curing temperatures as equivalent ages. The proposed equation can be used in the field for evaluating the strength after form removal.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.782-788
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• 2002

Several non-destructive test methods have been developed to estimate compressive strength of concrete in other countries. However, their applications are limited in domestic concrete due to their inaccuracies. The purpose of this study is to propose an aging coefficient of compressive strength of structural concrete in rebound number method and ultrasonic pulse velocity method for domestic concrete. The test variables include type of aggregate, curing condition, and compressive strength. Two approaches are used to estimate aging coefficient. One is evaluated by uniform linear regression equation for all ages and shows uniform strength reduction coefficient regardless of material properties and the other is evaluated by individual regression equation for each ages and shows nonuniform strength reduction and rebound increasing coefficients which decrease with increasing of rebound number and compressive strength. The latter result which can include the effect of rebound number and compressive strength is more resonable than the former.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 1998.10a
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• pp.146-149
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• 1998

In this study, the chloride ion penetration test and the compressive strength test should be done simultaneously on the standard cylinder specimen. And from analyzing the data from those tests, a strength estimation equation with high credibility is to be developed.

• Journal of Korean Society of Steel Construction
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• v.11 no.2 s.39
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• pp.233-240
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• 1999

It is well known that the ultimate compressive strength of concrete filled tubular stub-column is higher than that of the simplified evaluating value because of the confinement effect of infilled concrete. In this paper, It is compared the experimental results of other researchers with estimated ones by using the formulae. Finally, It is shown that the predicted equation is obtained by using the numerical analysis.