• Structural Engineering and Mechanics
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• v.15 no.2
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• pp.159-180
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• 2003

In this paper spacing and width of flexural cracks in reinforced concrete beams are determined using two-dimensional finite element analysis. At early loading stages on the beam the primary crack spacing is based on the slip length, which is the development length required to resist the steel stress increment that occurs at a cracked section on the formation of the first flexural crack. A semi-empirical formula is presented in this paper for the determination of the slip length for a given beam. At higher load levels, the crack spacing is based on critical crack spacing, which is defined as the particular crack spacing that would produce a concrete tensile stress equal to the flexural strength of concrete. The resulting crack width is calculated as the relative difference in extensions of steel reinforcement and adjacent concrete evaluated at the cracked section. Finally a comparative study is undertaken, which indicates that the spacing and width of cracks calculated by this method agree well with values measured by other investigators.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.4
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• pp.81-90
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• 2022

In this study, for one-way concrete slabs, the flexural strength, deflection, and crack width according to the amount of reinforcing bars were compared for the cases of using steel reinforcing bars and CFRP reinforcing bars. Critical performance dominating the flexural design was investigated and how to design the CFRP-reinforced concrete slab with efficiency was also discussed. It was found that CFRP-reinforced concrete slabs could achieve greater design flexural strength with the same amount of reinforcing bars compared to those using steel rebar, while deflection and crack width were relatively much larger. In concrete slabs using CFRP reinforcing bars, it was confirmed that the maximum crack width acts as a dominant factor in the design. For more efficient flexural design, it is necessary to mitigate the allowable crack width to 0.7 mm and to apply smaller diameter reinforcing bars to control the crack width.

• Journal of the Korea Concrete Institute
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• v.11 no.3
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• pp.69-80
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• 1999

The strengthening of reinforced concrete structures by externally bonded GFRP has become increasingly common in resent years. However the analysis and design method for GFRP plate strengthening of RC beams is not well established yet. The purpose of present paper is, therefore, to define the failure mechanism and failure behavior of strengthened RC beam using GFRP and then to propose a resonable method for the calculation of interface debonding load for those beams. From the experimental results of beams strengthened by GFRP, the influence of length and thickness, width of plate on the interfacial debonding failure behavior of beam is studied and, on the basis of test results, the semi-empirical equation to predict debonding load is developed. The proposed theory based on nonlinear analysis and critical flexural crack width, predicts relatively well the debonding failure load of test beams and may be efficiently used in the analysis and design of strengthened RC beams using GFRP.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.377-380
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• 1999

This paper dscribes an experimental investigation into the cause of flexural-shear failure in RC beams. The experimental variables are bottom flange width and tension bar location. Then these test results were compared and analyzed to deduce the major cause of critical-shear cracking. As a result, it was found that the propagation of the critical shear crack depended exclusively on the intensity of horizontal cracking.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.2
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• pp.79-87
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• 2011

In this study, the chloride penetration tests were performed for the initially cracked reinforced concrete members. The chloride diffusion characteristics and the critical crack width are compared, and the properties of self-healing are investigated. According to the test results, the chloride penetration resistance was greatly reduced as the surface crack width increased. When the mineral admixtures are added, the chloride penetration resistance of uncracked specimens were effectively increased, however, in case of the blast furnace slag and fly ash, the cracked specimens showed the more reduced resistance than OPC case, inversely. Also, the critical width was $29{\mu}m$, on average, for immersion test. The crack width with $4{\sim}15{\mu}m$ was restored by self-healing, The parts restored by self-healing were seemed to be visually restored, however, the chloride penetration resistance was not restored, perfectly.

• Proceedings of the Korea Concrete Institute Conference
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• 1992.10a
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• pp.202-207
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• 1992

The objective of this study is to develop analytical techniques of polymer impregnated concrete flexural members for its proper applications. crystalline methylmethacrylate(MMA) is chosen as a monomer of polymer impregnants, On the basis of members. fracture toughness, fracture energy , critical crack width, and tension softening relations near crack tip are formulated in terms of member depth, initial notch length and the flexural strength of normal concrete. The structural analysis rocedure and the finite element computer program developed in the study are applicable to evaluate elastic behavior, ultimate strength, and tension softening behavior of MMA type PIC structural members subject to various loading conditions. It is concluded that the developed structural analysis procedure and the finite element computer program are applicable to analysis and design of in-situ and precast PIC structural members.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.6 s.165
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• pp.1026-1038
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• 1999

Interlaminar fracture toughness of carbon/epoxy composite materials has been studied under tensile and flexural loading by the use of width tapered double cantilever beam(WTDCB) and end notched flexure(ENF) specimens. This study has significantly examined the effect of various interfacial ply orientation, ${\alpha}(0^{\circ},\;45^{\circ}\;and\;90^{\circ})$ and crack propagation direction, ${\theta}(0^{\circ},\;15^{\circ},\;30^{\circ}\;and\;45^{\circ})$ in terms of critical strain energy release rate through experiments. Twelve differently layered laminates were investigated. The data reduction for evaluating the fracture energy is based on compliance method and beam theory. Beam theory is used to analyze the effect of crack propagation direction. The geometry and lay-up sequence of specimens are considered various conditions such as skewness parameter, beam volume, and so on. The results show that the fiber bridging occurred due to the non-midplane crack propagation and causes the difference of fracture energy evaluated by both methods. For safer and more reliable composite structures, we obtain the optimal stacking sequence from initial fracture energy in each mode.

• Magazine of the Korea Concrete Institute
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• v.6 no.2
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• pp.97-107
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• 1994

The objective of this study is to develop polymer-impregnated concrete(PIC), which is a newly developed composite material made by impregnating polymer impregnanls into hardened normal concrete, and to develop analytical techniques for its proper applications. Crystalline methyl methacrylate(MMA) is chosen as a monomer of polymer impregnants. The corrlpositions of polymer impregnants and producing processes are developed by analyzing the effects of penetration, polymerization, thermal safety, and strengthening characteristics. On t he basis of experimental results of this study, various strength characteristics and stress strain constitutive relations are formulated in terms of the compressive strength of normal concrete and the polymer loadings, which can be applied for analysis and design of PIC members. In order to provide a model for fracture analysis of flexural members, fracture toughness, fracture energy, critical crack width, and tension softening relations near crack tip are also formulated in terms of member depth, initial notch depth, and the flexural strength of normal concrete. The structural analysis procedure and the finite element computer program developed in the study are applicable to evaluate elastic behavior, ultimate strength, and tension softening behavior of MMA type PIC structural members subject to various loading conditions. The accuracy and effectiveness of the developed computer program is examined by comparing the anal ytical results with the experimental results. Therefore, it is concluded that the developed structural analysis procedure and the finite element computer program are applicable to analysis and design of in-situ and precast PIC structural members.

• Structural Engineering and Mechanics
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• v.39 no.2
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• pp.241-266
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• 2011

The Self Compacting Concrete, SCC is the new generation type of concrete which is not needed to be compacted by vibrator and it will be compacted by its own weight. Since SCC is a new innovation and also the high strength self compacting concrete, HSSCC behavior is like a brittle material, therefore, understanding the strength effect on the serviceability performance of reinforced self compacting concretes is critical. For this aim, first the normal and high strength self compacting concrete, NSSCC and HSSCC was designed. Then, the serviceability performance of reinforced connections consisting of NSSCC and HSSCC were investigated. Twelve reinforced concrete connections (L = 3 m, b = 0.15 m, h = 0.3 m) were simulated, by this concretes, the maximum and minimum reinforcement ratios ${\rho}$ and ${\rho}^{\prime}$ (percentage of tensile and compressive steel reinforcement) are in accordance with the provision of the ACI-05 for conventional RC structures. This study was limited to the case of bending without axial load, utilizing simple connections loaded at mid span through a stub (b = 0.15 m, h = 0.3 m, L = 0.3 m) to simulate a beam-column connection. During the test, concrete and steel strains, deflections and crack widths were measured at different locations along each member. Based on the experimental readings and observations, the cracked moment of inertia ($I_{cr}$) of members was determined and the results were compared with some selective theoretical methods. Also, the flexural crack widths of the members were measured and the applicability for conventional vibrated concrete, as for ACI, BS and CSA code, was verified for SCCs members tested. A comparison between two Codes (ACI and CSA) for the theoretical values cracking moment is indicate that, irrespective of the concrete strength, for the specimens reported, the prediction values of two codes are almost equale. The experimental cracked moment of inertia $(I_{cr})_{\exp}$ is lower than its theoretical $(I_{cr})_{th}$ values, and therefore theoretically it is overestimated. Also, a general conclusion is that, by increasing the percentage of ${\rho}$, the value of $I_{cr}$ is increased.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.579-588
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• 2006

In recent years, the availability of high-strength reinforcing and prestressing steels leads us to build economically and efficiently designed concrete structural members. One of critical problems faced to the structural engineers dealing with these types of structural member is controls of crack width that is used as a criterion for the serviceability in the limit state design. Especially, flexural cracking must be controlled to secure the structural safety and to improve the durability as well as serviceability of the load carving members. The proposed method utilizes the results of pure tension test in which tensile loads are applied both side of specimen, done by Ikki. The bond characteristics of deformed reinforcing bar under pure tension is considered by the area of concrete and rib area. The results of proposed method are compared with the test data and the results show that the proposed method can take into account the dimensions, variation of sectional properties, and direction of reinforcing and gives more accurate maximum bond stress and corresponding relative slip than the existing methods. the characteristics of bonding is considered by using dimensionless slip magnitude and effective reinforcement ratio. The validity of the proposed equation is verified by test experimental data.