• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.189-194
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• 2001

In this study, ultimate strength of concrete deep beams with an opening is predicted by using Strut-and-Tie Model with a new effective compressive strength. First crack occurs around an opening by stress concentration due to geometric discontinuity. This results in decreasing ultimate strength of deep beams with an opening compared with general deep beams. With fundamental notion that ultimate strength of deep beam with an opening decreases as a result of reduction in effective compressive strength of a concrete strut, an equivalent effective compressive strength formula is proposed in order to reflect ultimate strength reduction due to an opening located in a concrete strut. An equivalent effective compressive strength formula which can reflect opening size and position is added to a testified algorithm of predicting ultimate strength of concrete deep beams. Therefore, ultimate strength of concrete deep beam with an opening is predicted by using a simple and rational STM algorithm including an equivalent effective compressive strength formula, not by finite element analysis or a former complex Strut-and-Tie Model

• Structural Engineering and Mechanics
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• v.74 no.3
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• pp.435-443
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• 2020

The objective of this study was to determine the effective compressive strength of a column-slab connection with different compressive strengths between the column and slab concrete. A total of eight column specimens were fabricated, among which four specimens were restrained by slabs while the others did not have any slab, and the test results were compared with current design codes. According to ACI 318, the compressive strength of a column can be used as the effective compressive strength of the column-slab connection in design when the strength ratio of column concrete to slab concrete is less than 1.4. Even in this case, however, this study showed that the effective compressive strength decreased. The specimen with its slab-column connection zone reinforced by steel fibers showed an increased effective compressive strength compared to that of the specimen without the reinforcement, and the interior column specimens restrained with slabs reached the compressive strength of the column.

• Journal of the Korea Institute of Building Construction
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• v.2 no.4
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• pp.163-168
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• 2002

The object of this study is to define the characteristics of high performance concrete with varing compressive strength of concrete and curing temperature. The major test variables are 1) high strength concrete(500kg/$cm^2$) and ordinary strength concrete(240kg/$cm^2$) compressive strength, 2) curing temperature and condition, 3) concrete curing age, 4) three types of cement. From the test results were shown that curing temperature and curing conditions were also very effective for high strength concrete and ordinary strength concrete, and concrete were largely effected by cement type and temperature during the hydration reaction process. This paper describes the effect of curing temperature for strength and characteristics of high performance concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.397-400
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• 2002

The mechanical properties of concrete such as modulus of elasticity, bond strength and shear strength are proportional to square root of compressive strength. And compressive strength of concrete is developed rapidly at early ages. Thus the relationship between compressive strength and its mechanical properties should be verified because the mechanical properties of early age concrete and hardened concrete are different. In this study, to predict the concrete slab deflection at early ages, modulus of elasticity and effective moment of inertia(Ie) are observed and compared with experimental results.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.267-272
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• 1995

The objective of this study is to investigate the effect of concrete strength on the stirrup effectiveness factor(K) of reinforced concrete beams with stirrup based on previous test results(a/d$\geq$2.5). In the procedure of the estimation of K, it was assumed that the ultimate shear strength for beams without stirrup is equal to the concrete contribution to shear strength for beam with stirrup. A model equation for calculation the stirrup of compressive strength of concrete. It was shown that the stirrup effective factor of compressive strength of concrete. It wah shown that the stirrup effective factor is greater than 1.0 up to compressive strength 85MPa. Therefore the current ACI Code equation for predicting the shear strength and the stirrup effectiveness factor of 1.0 is conservative for nomal and high stength concrete beams with stirrup.

• Structural Engineering and Mechanics
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• v.45 no.6
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• pp.837-851
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• 2013

In construction industry, strength is a primary criterion in selecting a concrete for a particular application. The concrete used for construction gains strength over a long period of time after pouring the concrete. The characteristic strength of concrete is defined as the compressive strength of a sample that has been aged for 28 days. Neither waiting for 28 days for such a test would serve the rapidity of construction, nor would neglecting it serve the quality control process on concrete in large construction sites. Therefore, rapid and reliable prediction of the strength of concrete would be of great significance. On this backdrop, the method is proposed to establish a predictive relationship between properties and proportions of ingredients of concrete, compaction factor, weight of concrete cubes and strength of concrete whereby the strength of concrete can be predicted at early age. Multiple regression analysis was carried out for predicting the compressive strength of concrete containing Portland Pozolana cement using statistical analysis for the concrete data obtained from the experimental work done in this study. The multiple linear regression models yielded fairly good correlation coefficient for the prediction of compressive strength for 7, 28 and 40 days curing. The results indicate that the proposed regression models are effectively capable of evaluating the compressive strength of the concrete containing Portaland Pozolana Cement. The derived formulas are very simple, straightforward and provide an effective analysis tool accessible to practicing engineers.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04a
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• pp.83-88
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• 1998

II-anhydrite, slag, and fly ash produced as industrial by-product were reutilized for the manufacture of high strength admixtures for cement and concrete. The effects of these admixtures on the compressive strength of cement mortar and concrete were examined with those of domestic admixture. At the condition mortar and concrete. Especially, adding of II-anhydrite was very effective for the increasing of compressive strength. Therefore it is possible that these admixture as a high strength admixture apply to cement and concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 1990.10a
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• pp.125-130
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• 1990

Fly Ash in concrete is known to be effective in improving workability, the reduction of heat of hydration, increasing the long-term compressive strength, and improving durability. Recently, fly ash is consedered an essential material for the high-strength concrete. In this paper, investigations for the strength and workability characteristics was carried out when fly ash was used in the high-strength concrete. As the result, fly ash was effective in increasing the long-term compressive strength, but the short-term compressive strength was gradually decreased with increating fly ash contents. And also the use of superplasticzers was required for providing the proper workability when fly ash contents were increased. The optimum content of fly ash was about 10%.

• Journal of the Korea Concrete Institute
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• v.12 no.2
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• pp.71-78
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• 2000

This paper presents a study on the flexural rigidity of reinforced high strength concrete beams. Thirty six beams with different compressive strength of concrete, tensile reinforcement ratio, compressive reinforcement ratio, and pattern of loadings(1 point loading and 2 points loading) were tested to evaluate the effective moment of inertia. According to the experimental results, the eqation(1) proposed by ACI code for the effective moment of inertia overestimated that of simply supported reinforced high strength concrete beams. Thus, in this paper, an empirical equation(3) is proposed as a lower bound of 90% confidence limit to estimate the effective moment of inertia of simply supported reinforced high strength concrete beams.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.241-246
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• 2000

In the strut-tie model design of structural concrete, the importance of the effective strength of concrete strut has been overlooked by many practitioners. The authors believe that the effective strength of concrete strut is an important factor not only in determining steel tie forces but also in verifying the nodal zone strength and geometric compatibility condition of a selected strut-tie model. This study evaluate the effect of the effective strength of concrete strut on structural concrete design by applying the different effective strut strengths to the strut-tie model design of a post-tensioned anchorage zone and a continuous concrete deep beam.