• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.677-682
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• 2001

In this study, a method to evaluate diffusion coefficient of chloride ion in cracked concrete is proposed. For cracked concrete having either anisotropic or isotropic crack network, each crack of saturated concrete is considered as a V shape crack, and an effective diffusion coefficient is expressed with diffusion coefficients of cracked part and noncracked part and a so-called crack spacing factor. A comparison with experimental results shows that the diffusion coefficient for cracked concrete is accurately predicted by the effective diffusion coefficient. Prediction results also show that the cracks in concrete markedly change the diffusion properties and accelerate penetration of drifting species. The method in this paper can be effectively used to consider the effect of cracks on concrete diffusion coefficient of cracked concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.655-660
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• 2002

Major deterioration in concrete structures are salt attack and carbonation. Especially severe problems due to carbonation occur in tile concrete structures of city, tunnel, underground structures. Cracks in concrete during service life including early age due to hydration heat and/or shrinkage accelerate the diffusion of concrete so that the deterioration is also accelerated. In this study, carbonation depths of both non-cracked concrete and cracked concrete are evaluated and weight change test and TGA are carried out. Through the tests, a relation between water-cement ratio and carbonation depth is derived and also carbonation increase rate is derived in the function of crack width.

• Journal of Korean Society of Steel Construction
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• v.27 no.1
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• pp.87-97
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• 2015

In this study, an experimental study was performed to evaluate the concrete breakout strength of cast-in-place(CIP) anchors in cracked concrete under static shear loading. The CIP anchors involved in this study were 30mm in diameter with an edge distance of 150mm and an embedment length of 240mm. The experiment was carried out for two specimens in uncracked concrete and three specimens in cracked concrete orthogonal and parallel to the direction of shear loading, respectively. Compared to the uncracked concrete specimen, cracked specimen orthogonal to the direction of shear loading showed no reduction in the concrete breakout strength and that parallel to the load direction about 91% strength which corresponds to 84% of uncracked concrete strength defined in ACI 318-11. Therefore, the experimental results showed smaller decrease in the shear resistance of CIP anchors in cracked concrete than that specified in ACI code which account for 71% strength of uncracked concrete in cracked concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.455-460
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• 2002

In this study, a numerical analysis that can effectively predict the effect of strengthening of cracked flexural members is developed using axial deformation link elements. Concrete and interface between concrete and repair material are considered as quasi-brittle material. Reinforcing bars and reinforcing steel plates are assumed to perform as elasto-plastic materials. Unloading behavior of axial deformation link element is implemented. In the developed numerical model, a flexural member is intentionally cracked by pre-loading, then, the cracked member is repaired using extra elements, and reloaded. The results from analysis of repaired flexural members agrees well with available experiment results. Also, it was shown that the effect of strengthening and the change of failure mode with respect to the time for strengthening and thickness of repair materials. Based on the results, it was determined that the developed numerical model has a good agreement for determining failure modes and effect of strengthening in cracked flexural members. By utilizing the developed numerical analysis, the time and dimension of external strengthening in an existing cracked flexural member with predition of failure mechanism can be determined.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.1
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• pp.22-33
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• 2015

Chloride ions in RC (Reinforced Concrete) structures can cause very severe corrosion in reinforcement steel. It is generally informed that chloride penetration can be considerably accelerated by enlarged chloride diffusion due to cracks. These cracks play a role in main routes through which chloride ions penetrate into the concrete, and also lead to steel corrosion in RC structures exposed to chloride attack, such as port and ocean structures. In this paper, field survey including evaluation of crack and chloride concentration distribution in concrete is performed to investigate an effect of crack on chloride diffusion. The service life of cracked concrete exposed to the marine environmental condition is estimated considering the crack effect on chloride diffusion. For this purpose, diffusion coefficients in cracked concrete are obtained based on the field survey. Using the relationship between diffusion coefficients in the cracked concrete and the crack widths, service life of the cracked concrete is predicted in a probabilistic framework. A bimodal distribution with two peaks, consisting of a weighted sum of two normal distributions is introduced to describe chloride diffusion of the concrete wharf with crack.

• Structural Engineering and Mechanics
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• v.40 no.1
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• pp.105-120
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• 2011

The strengthening and rehabilitation of reinforced concrete structures with externally bonded carbon fibre reinforced polymer (FRP) laminates has shown excellent performance and, as a result, this technology is rapidly replacing steel plate bonding techniques. This paper addresses this issue, and presents results deals with the influence of external bonded CFRP-reinforcement on the time-dependent behavior of reinforced concrete beams. A total of eight reinforced concrete beams with cracked and un-cracked section, with and without externally bonded CFRP laminates, were investigated for their creep and shrinkage behavior. All the beams considered in this paper were simply supported and subjected to a uniform sustained loading for the period of six months. The main parameters of this study are two types of sustained load and different degrees of strengthening scheme for both cracked and un-cracked sections of beams. Both analytical and experimental work has been carried out on strengthened beams to investigate the cracking and deflection performance. The applied sustained load was 56% and 38% of the ultimate static capacities of the un-strengthened beams for cracked and un-cracked section respectively. The analytical values based on effective modulus method (EMM) are compared to the experimental results and it is found that the analytical values are in general give conservative estimates of the experimental results. It was concluded that the attachment of CFRP composite laminates has a positive influence on the long term performance of strengthened beams.

• Structural Engineering and Mechanics
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• v.10 no.5
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• pp.463-478
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• 2000

An iterative procedure for the analysis of reinforced concrete frames with beams in cracked state is presented. ACI and CEB model equations are used for the effective moment of inertia of the cracked members. In the analysis, shear deformations are taken into account and reduced shear stiffness is considered by using effective shear modulus models available in the literature. Based on the aforementioned procedure, a computer program has been developed. The results of the computer program have been compared with the experimental results available in the literature and found to be in good agreement. Finally, a parametric study is carried out on a two story reinforced concrete frame.

• Journal of the Korea Concrete Institute
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• v.11 no.5
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• pp.79-88
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• 1999

The purpose of this paper is to develop a mathematical expression for computing crack angles based on reinforcement volumes in the longitudinal and transverse directions, member end-fixity and length-to-width aspect ratio. For this a reinforced concrete beam-column element is assumed to possess a series of potential crack planes represented by a number of differential truss elements. Depending on the boundary condition, a constant angle truss or a variable angle truss is employed to model the cracked structural concrete member. The truss models are then analyzed using the virtual work method of analysis to relate forces and deformations. Rigorous and simplified solution schemes are presented. An equation to estimate the theoretical crack angle is derived by considering the energy minimization on the virtual work done over both the shear and flexural components the energy minimization on the virtual work done over both the shear and flexural components of truss models. The crack angle in this study is defined as the steepest one among fan-shaped angles measured from the longitudinal axis of the member to the diagonal crack. The theoretical crack angle predictions are validated against experimentally observed crack angle reported by previous researchers in the literature. Good agreement between theory and experiment is obtained.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10a
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• pp.399-404
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• 1998

Analysis of partially prestressed beams in which cracking under service loads is allowed requires a knowledge of geometric cross section properties such as neutral axis, centroid, area and moment of initia of this cracked transformed section. Especially an exact calculation for the stresses of steel and concrete and the width of crack and the amount of deflection can be obtained with accrurate prediction of neutral of centroidal axis location. In this paper, the procedures for predicting the centroidal axis location of partially cracked prestressed concrete members, using the compatibility of deformation of concrete and steel are formulated and compared with Dilger`s computed results. And also the computed results according to this paper are compared with Branson`s experimental results.

• International Journal of Concrete Structures and Materials
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• v.5 no.1
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• pp.11-18
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• 2011

Carbonation in RC (reinforced concrete) structure is considered as one of the most critical deteriorations in urban cities. Although RC column has one mix condition, carbonation depth is measured spatially differently due to its various environmental and internal conditions such as sound, cracked, and joint concrete. In this paper, field investigation was performed for 27 RC columns subjected to carbonation for eighteen years. Through this investigation, carbonation distribution in sound, cracked, and joint concrete were derived with crack mappings. Considering each related area and calculated PDF (probability of durability failure) of sound, cracked, and joint concrete through Monte Carlo Simulation (MCS), repairing timings for RC columns are derived based on several IPDF (intended probability of durability failure) of 1, 3, and 5%. The technique of equivalent probability including carbonation behaviors which are obtained from different conditions can provide the reasonable repairing strategy and the priority order for repairing in a given traffic service area.