• Computers and Concrete
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• 제19권4호
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• pp.387-394
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• 2017

To study the effects of water-cement ratio changes and cracks on chloride ion transmission rate in cracked concrete, RCM method was adopted to accelerate the diffusion of chloride ion in cracked concrete, and the changes in chloride ion concentration and around the cracks are inferred by finite-element method. The test results show that as far as prefabricated cracks on concrete components are concerned, the width thresholds of two cracks on the concrete specimens with a water-cement ratio of 0.5 and 0.6 are 0.05 mm and 0.1 mm respectively, the width threshold of two cracks on the concrete specimens with a water-cement ratio of 0.4 is 0.05 mm and 0.2 mm respectively; and the results of numerical simulation show that the smaller the water-cement ratio is, the more significant effects of cracks on chloride ion transmission rate are. As a result, more attention shall be paid to the crack prevention, repairing and strengthening for high-strength concrete.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.647-650
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• 2003

Under sustained loads, the deformation of a structure gradually increase with time and eventually may be much greater than its instantaneous value, This inelastic and time-dependent deformation causes increase in deflection and curvature, redistribution of stress and internal action, In this paper, time-dependent analysis with creep and shrinkage of uncracked and cracked partially prestressed concrete flexural members is presented.

• 한국농공학회지
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• 제34권2호
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• pp.49-59
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• 1992

In our researches we made mix-design, with the mixing ratio and pre-cracked ratio of steel fibrous different from each other, building the steel fibrous concrete beam which had pre-cracks. To obtain the fracture characteristics of steel fibrous reinforced concrete, series of experiment were conducted on pre-cracked beam subjected to 3-point bending. Thus, we carried out experiments on the destructive characteristics of its pre-crack and post-crack and the result is as follows. 1. The compressive strength of steel fibrous concrete beam increased more slightly than plane beam, and the tensile strength increased 37%, 59%, 94% and 121% respectively when the amount of fibrous was 0.5%, 0.1% 1.5%, and 1.75% respectively. 2. As the amount of steel fibrous mixing increased ant the steel fibrous inhibited the crack growth, the crack condition of steel fibrous concrete beam was retarded irregularly, and this increased fracture load. 3. The defiance of destruction was reduced in the ratio of 1.35 times and 1.22 times respectively when the length of pre-crack was each 2cm and 4cm in comparison with the case of being without the length, and was similar to that of plane beam when the amount of steel fibrous mixing was below 1.0%, and increased linearly when it as above 1.0%. 4. The experimental formula seeking fracture energy was follows and thus we found that the value of fracture energy depended upon tensile strength and the size of speciment. $G_f=K\;{\cdot}\;f_f^'{\cdot}$da/Ec 5. We observed that in the load-strain curve of steel fibrous concrete beam the progress of the crack became slow, compared with plane beam because the crack condition became long to the extent of about 10 times. Concrete was faultiest brittleness fracture through the study, it was known ductile.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표논문집(II)
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• pp.462-467
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• 1998

A rational method for prediction of long-term deflections of reinforced concrete beams under sustained loads was proposed. Strain and stress distributions of uncracked and fully cracked sections after creep and shrinkage were determined from the requirements of strain compatibility and force equilibrium of a section, and then long-term deflections were calculated from the section analysis results. In fully cracked section analysis, noncoincidence of the neutral axis of strain and the neutral axis of stress after creep and shrinkage was taken into account. The accuracy of the proposed method was verified by comparison with several experimental measurements of beam deflections. The proposed approximate procedure gave the better predictions than the existing approximate methods. At the same time, the proposed method also retained simplicity of the calculation, since maximum long-term deflection could be obtained without tedious integration of the curvatures.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1994년도 봄 학술발표회 논문집
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• pp.25-29
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• 1994

A series of 6 reinforced concrete beams was tested to verify the effects of EBSP strengthened on cracked beams and to identify the various parameters affecting structure strengthening design(SSD). The parameters were the cross-sectional area of steel plates, the thickness of steel plates, and bond length of steel plates. In addition to these parameters, the effect of existing cracks on the strengthening was investigated. Test results show that EBSP is very effective and predictable for strengthening damaged structures. The results also show that the bond length of steel plates is the most important factor to develop ultimate load carrying capacities of strengthened beams. However, considerations in SSD should be given to assure the ductile failure at ultimate load such as the low ratio of thickness to the width of plates.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.806-809
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• 2004

The early-age cracks have bad effects on the diffusion movement of chloride ions and oxygen. In this study, a corrosion analysis algorithm for cracked concrete is proposed to examine the influence of early-age cracks on corrosion of RC structures. For different environmental exposure conditions of RC structures, a corrosion model is combined with models for activation polarization and concentration polarization. From the finite element corrosion analysis using the proposed algorithm and the models, the effects of early-age cracks to the corrosion is simulated.

• Computers and Concrete
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• 제1권1호
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• pp.77-98
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• 2004

This paper presents a numerical model for simulating the nonlinear response of reinforced concrete (RC) shear walls subject to cyclic loadings. The material behavior of cracked concrete is described by an orthotropic constitutive relation with tension-stiffening and compression softening effects defining equivalent uniaxial stress-strain relation in the axes of orthotropy. Especially in making analytical predictions for inelastic behaviors of RC walls under reversed cyclic loading, some influencing factors inducing the material nonlinearities have been considered. A simple hysteretic stress-strain relation of concrete, which crosses the tension-compression region, is defined. Modification of the hysteretic stress-strain relation of steel is also introduced to reflect a pinching effect depending on the shear span ratio and to represent an average stress distribution in a cracked RC element, respectively. To assess the applicability of the constitutive model for RC element, analytical results are compared with idealized shear panel and shear wall test results under monotonic and cyclic shear loadings.

• Computers and Concrete
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• 제22권4호
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• pp.373-381
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• 2018

Hollow center cracked disc (HCCD) in Brazilian test was modelled numerically to study the crack propagation in the pre-cracked disc. The pre-existing edge cracks in the disc models were considered to investigate the crack propagation and coalescence paths within the modelled samples. The effect of particle size on the hollow center cracked disc (HCCD) in Brazilian test were considered too. The results shows that Failure pattern is constant by increasing the ball diameter. Tensile cracks are dominant mode of failure. These crack initiates from notch tip, propagate parallel to loading axis and coalescence with upper model boundary. Number of cracks increase by decreasing the ball diameter. Also, tensile fracture toughness was decreased with increasing the particle size. In this research, it is tried to improve the understanding of the crack propagation and crack coalescence phenomena in brittle materials which is of paramount importance in the stability analyses of rock and concrete structures, such as the underground openings, rock slopes and tunnel construction.

• 대한건축학회논문집:구조계
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• 제34권11호
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• pp.19-26
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• 2018

This paper presents the shear strengthening effect of externally post-tensioning (EPT) method using high-strength steel rod in pre-cracked reinforced concrete (RC) beams. Three- and four-point bending tests were performed on a total of 8 specimens by adjusting the strengthening depths in the deviator position of EPT. The effective strengthening depths were 435, 535, and 610 mm. The pre-loading up to about 2/3 of ultimate load capacity measured in unstrengthened RC beam were applied in the beam to be post-tensioned. The EPT method was then applied to the pre-damaged RC beams and re-loading was added until the end of the test. EPT restored deflections of 3 mm or more, which account for about 40% of deflection when the pre-loading was applied. The shear strengthening increases more than 3 times and 36~107% in terms of the stiffness and load-carrying capacity compared to unstrengthening RC beams. The increased load-carrying capacities of the post-tensioned beam with strengthening depths of 435 and 535 mm are almost the same as 36~61%, and those of 610 mm are 84~107%, which shows the greatest shear strengthening effect.

• KCI Concrete Journal
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• 제12권2호
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• pp.55-72
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• 2000

This paper proposes a mechanical model to describe the load-deformation responses of the reinforced concrete plate members under service load state. An Analytical method is introduced on the basis of the rotating crack model which considers equilibrium, compatibility conditions, load-strain relationship of cracked member, and constitutive law for materials. The tension stiffening effect in reinforced concrete structures is taken into account by the average tensile stress-strain relationship from the load-strain relationship for the cracked member and the constitutive law for material. The strain compatibility is used to find out the crack direction because the crack direction is an unknown variable in the equilibrium and compatibility conditions. The proposed theory is verified by the numerous experimental data such as the crack direction, moment-steel strain relationship, moment-crack width relationship. The present paper can provide some basis for the provision of the definition of serviceability for plate structures of which reinforcements are deviated from the principal stresses, because the present code defines the serviceability by the deflection, crack control, vibration and fatigue basically for the skeletal members. The proposed theory is applicable to predict the service load state behavior of a variety of reinforced concrete plate structures such as skew slab bridges, the deck of skew girder bridges.