• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
• /
• pp.615-618
• /
• 2005

This study concerns the equation of high strength concrete by schmidt hammer test. There are not only few prediction strength equations of concrete by schmidt hammer test, but also many problems to apply them because of time, cost, easiness, structural damage, reliability and so on. For this study, there performed a series of schmidt hammer test with in existing 1,095days' concrete structures and proposed equations as follows ; Linear: ${\Large f}_{ck}=-45.35+2.44R(r^2=72.7\%)$ Quadratic: ${\Large f}_{ck}=-502.08+24.0R-0.25R^2(r^2=82.4\%)$ here, $f_{ck}$ : Estimated compressive strength of concrete by MPa, R : Rebound index of concrete

• 한국구조물진단유지관리공학회 논문집
• /
• 제4권1호
• /
• pp.121-129
• /
• 2000

In general. service life of the sea-shore concrete structures is largely influenced by the corrosion of reinforcing steel due to the chloride contamination, and the penetration of chloride ions into concrete is governed by concrete condition state as a micro-structure. In this study, characteristics of chloride diffusion in concrete are analyzed in accordance with the mixing properties and durability of concrete, by considering the facts that micro-structure of concrete varies with the mixing properties and can indirectly be analyzed by using the durability test. In order to predict the service life of existing concrete structures, chloride diffusion equation for the concrete structures under various service conditions and the major parameters used in that equation are formulated as the mathematical models. Based on the results of chloride diffusion analysis in accordance with the mixing properties and durability of concrete and mathematical models formulated in this study, a prediction system is developed to predict the corrosion initiation of reinforcing steel in the sea-shore concrete structures.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 1993년도 봄 학술발표회 논문집
• /
• pp.124-129
• /
• 1993

In this study, a simple and accurate model equation for prediction of shear strength of reinforce concrete beams without web, reinforcement is proposed based on basic shear transfer mechanism and modified Bazant's size effect law. The proposed equation includes the effects of concrete strength, longitudinal steel ratio, shear span to depth ratio and effective depth. Comparisons with published experimental data indicate that the proposed equation estimates properly the effects of these factors. Among many equations, ACI code equation, Zsutty's equation and Bazant's equation are selected for comparison. As the result, the accuracy of the proposed equation is better than that of any other equations.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
• /
• pp.878-883
• /
• 2003

To modify some problems of ACI shear provisions, ultimate shear strength equation considering size effect and arch action to compute shear strength in high-strength concrete beams without stirrups is presented in this research. Three basic equations, namely size reduction factor, rho factor, and arch action factor, are derived from crack band model of fracture mechanics, analysis of previous some shear equations for longitudinal reinforcement ratio, and concrete strut described as linear function in deep beams. Constants of basic equations are determined using statistical analysis of previous shear testing data. To verify proposed shear equation for each variable, namely d, , ρ, f/sub c/' and aid, about 250 experimental data are used and proposed shear equation is compared with ACI 318-99 code, CEB-FIP Model code, Kim & Park's equation and Zsutty's equation. While proposed shear equation is simpler than other shear equations, it is shown to be economical predictions and reasonable safety margin. Hence proposed shear strength equation is expected to be applied to practice shear design.

• Computers and Concrete
• /
• 제12권4호
• /
• pp.377-392
• /
• 2013

This paper investigates prediction models estimating the hydration properties of concrete, such as the compressive strength, the splitting tensile strength, the elastic modulus,and the autogenous shrinkage. A prediction model is suggested on the basis of an equation that is formulated to predict the compressive strength. Based on the assumption that the apparent activation energy is a characteristic property of concrete, a prediction model for the compressive strength is applied to hydration-related properties. The hydration properties predicted by the model are compared with experimental results, and it is concluded that the prediction model properly estimates the splitting tensile strength, elastic modulus, and autogenous shrinkage as well as the compressive strength of concrete.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 1991년도 가을 학술발표회 논문집
• /
• pp.51-58
• /
• 1991

In staically indeterminate structures torsional stiffness is an important factor for prediction of mechanical behavior at all loading stages in reinfored concrete beams, which also for calculation of torsional moment. This paper proposes equation for postcracking torsional stiffness of reinforced concrete beams under pure torsion, which is derived considering the equilibrium and compatibility condition for shear panel based on the variable angle space truss model. The equation describes well the effect according to the variation of aspect ratio and steel volume ratio per unit concrete volume. It agress with experimental results in this paper as well as available literature.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2023년도 가을학술발표대회논문집
• /
• pp.149-150
• /
• 2023

This study proposes the most suitable strength prediction model equation for UHPC by calculating the apparent activation energy of UHPC according to the curing temperature and deriving the integrated temperature and compressive strength prediction equation. The results are summarized as follows. The apparent activation energy was calculated using the Arrhenius function, which was calculated as 21.09 KJ/mol. A model equation suitable for UHPC was calculated, and when the Flowman model equation was used, it was confirmed that it was suitable for the properties of UHPC using a condensation promoting super plasticizing agent.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
• /
• pp.259-264
• /
• 1999

The aim of this study of to compare the development of compressive strength of high-strength concrete with maturity and investigate the applicability the strength prediction models. An experiment was attempted on the high-strength concrete mixes using portland cement replaced by silica fume of 10% by weight of cement, the water-binder ratios of mixes being 0.30 and 0.35, the curing temperatures being 30, 20, 10, 5$^{\circ}C$. Test results of mixes are statistically analyzed to infer the correlation coefficient between the maturity and the compressive strength of high-strength concrete. The constant of strength prediction equation were determined from test results, and the equation was adopted to predict the strength of slab(W80$\times$D100$\times$H20cm). The slab was cast in the laboratory from the same batch water-binder ratio of 0.30, and cores were cut from slab in order to estimate the actual strength. These values are used to compare with predicted value. The present study allows more realistic determination of early age compressive strength of high-strength concrete and can be efficiently used to control the quality in actual construction.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
• /
• pp.739-742
• /
• 1999

A reinforcement corrosion prediction model was proposed using the results from accelerated testing and mathematical equation from the Fick's 2nd law for chloride-induced corrosion of reinforcement in concrete. The input data included the chloride concentration, mix characteristics of concrete, and environmental conditions. This model can be used to predict the chloride concentration pertaining to corrosion time and loading age for marine concrete structures. This model can also be used to predict the service life.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
• /
• pp.247-252
• /
• 2002

The evaluation equation of torsional moment for reinforced concrete members in ACI 318-99 ignores the contribution of concrete, T$_{c}$. Several research indicates that the torsional moment of concrete is in effect, specially for the members in which the longitudinal and transverse reinforcement content is small. This paper proposes an evaluation equation of torsional moment taking into account the contribution of concrete. According to the comparison with the 66 test results, the torsion equation in ACI code underestimated or overestimated the real torsional moment of reinforced concrete beams. On the other hand, the proposed torsional equation is shown to be in a good agreement with experimental results.s.