• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.320-324
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• 2013

A crack identification method using an equivalent bending stiffness for cracked beam and committee of neural networks is presented. The equivalent bending stiffness is constructed based on an energy method for a straight thin-walled pipe, which has a through-the-thickness crack, subjected to bending. Several numerical analysis for a steel cantilever pipe using the equivalent bending stiffness are carried out to extract the natural frequencies and mode shapes of the cracked beam. The extracted modal properties are used in constructing a training patterns of a neural network. The input to the neural network consists of the modal properties and the output is composed of the crack location and size. Multiple neural networks are constructed and each individual network is trained independently with different initial synaptic weights. Then, the estimated crack locations and sizes from different neural networks are averaged. Experimental crack detection is carried out for 3 damage cases using the proposed method, and the identified crack locations and sizes agree reasonably well with the exact values.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.87-92
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• 2001

Reinforced concrete have defect in durability due to carbonation, freezing and thawing, and penetration of chloride ions with time in spite of superb structure. Especially steel corrosion in concrete due to penetration of chloride ions have result in a marked decline in service life. The principal purpose in this study is to see effect of sacrificial anode cathodic system, one of the electrochemical methods in order to the control of steel corrosion in concrete. There are chloride content in concrete in cracked and no cracked specimen with cathodic protection. To recognize the effect of sacrificial anode cathodic protection, Instant-off potential are measured. We have the excellent effect for control steel corrosion adaption sacrificial anode cathodic system.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.04a
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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.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.1207-1212
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• 2001

Reinforced concrete has defects in durability due to carbonation, freezing and thawing, and penetration of chloride ions with elapse of time in spite of super structure. Especially steel corrosion in concrete due to penetration of chloride ions has result in a severe decline in service life. The principal purpose of this study is to estimate effects of sacrificial anode cathodic system, one of the electrochemical methods in order to control of steel corrosion in concrete. There are chloride content in concrete in cracked and non cracked specimen with cathodic protection. To investigate the effect of sacrificial anode cathodic protection, potential-decay with current density, corrosion ratio, etc. are measured. We have the excellent effect for control steel corrosion adaption sacrificial anode cathodic system.

• Structural Engineering and Mechanics
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• v.38 no.1
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• pp.81-97
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• 2011

In this research, the wavelet transform is used to analyze time response of a cracked beam carrying moving mass for damage detection. In this respect, a new damage detection method based on the combined use of continuous and discrete wavelet transforms is proposed. It is shown that this method is more capable in making damage signature evident than the traditional two approaches based on direct investigation of the wavelet coefficients of structural response. By the proposed method, it is concluded that strain data outperforms displacement data at the same point in revealing damage signature. In addition, influence of moving mass-induced terms such as gravitational, Coriolis, centrifuge forces, and pure inertia force along the deflection direction to damage detection is investigated on a sample case. From this analysis it is concluded that centrifuge force has the most influence on making both displacement and strain data damage-sensitive. The Coriolis effect is the second to improve the damage-sensitivity of data. However, its impact is considerably less than the former. The rest, on the other hand, are observed to be insufficient alone.

• Journal of Ocean Engineering and Technology
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• v.9 no.1
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• pp.83-91
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• 1995

Surface defects in structural members are apt to be origins of fatigue cracks growth, which may cause serious failure of whole structures. Most structure has a part where stress concentrates such as welded joints, corner parts, etc. And then, analysis on crack growth and penetration from these defects, therefore, is one of the most important subjects for the reliability of LBB design. The present paper has performed an experimental and analysis on the fatigue crack propagation by variety in crack length of surface cracked plate with stress concentration part. The crack growth behavior can be explained quantitatively by using Newman-Raju equation and the stress partitioning method proposed by ASME B&P Code Sec. XI. The stress concentration factor $K_t$ has affected on the crack growth. The crack growth after penetration depends upon the initial front side crack length.

• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.67-70
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• 2008

This study is to analyzes the global behavior of frame structures with local cracks in structural members by frame analysis, using the stiffness matrix of cracked frame element. This local compliance is utilized to derive the stiffness matrix of the cracked frame element and the effects of interaction among multiple cracks are also examined. The proposed technique is applied to frame structures with local cracks. Analysis results confirm the possibility of quantitative analysis of a structure damaged with local cracks and the feasibility of the technique as a tool for analyzing the global behavior of frame structures, reflecting effects of local cracks.

• Advances in aircraft and spacecraft science
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• v.7 no.2
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• pp.151-168
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• 2020

The present study deals with the repair of composite structures by bonding composite patches. The composite structure is a carbon/epoxy laminate with stacking sequence [45/-45/0/90]S. The damaged zone is simulated by a central crack and repaired by bonding symmetrical composite patches. The repair is carried out using composite patches laminated from the same elemental folds as those of the cracked specimen. Three-dimensional finite element method is used to determine the energy release rate along the front of repaired crack. The effects of the repair technique used single or double patch, the stacking sequence of the cracked composite patch and the adhesive properties were highlighted on the variations of the fracture energy in mode I and mixed mode I + II loading.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.4
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• pp.391-399
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• 2008

In this paper, we further generalize the work of Lin and Abel to the case of the first and the second order derivatives of energy release rates for two-dimensional, multiply cracked systems. The direct integral expressions are presented for the energy release rates and their first and second order derivatives. The salient feature of this numerical method is that the energy release rates and their first and second order derivatives can be computed in a single analysis. It is demonstrated through a set of examples that the proposed method gives expectedly decreasing, but acceptably accurate results for the energy release rates and their first and second order derivatives. The computed errors were approximately 0.5% for the energy release rates, $3\sim5%$ for their first order derivatives and $10\sim20%$ for their second order derivatives for the mesh densities used in the examples. Potential applications of the present method include a universal size effect model and a probabilistic fracture analysis of cracked structures.

• Structural Engineering and Mechanics
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• v.31 no.2
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• pp.163-180
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• 2009

In the design of tall reinforced concrete (R/C) buildings, the serviceability stiffness criteria in terms of maximum lateral displacement and inter-story drift must be satisfied to prevent large second-order P-delta effects. To accurately assess the lateral deflection and stiffness of tall R/C structures, cracked members in these structures need to be identified and their effective member flexural stiffness determined. In addition, the implementation of the geometric nonlinearity in the analysis can be significant for an accurate prediction of lateral deflection of the structure, particularly in the case of tall R/C building under lateral loading. It can therefore be important to consider the cracking effect together with the geometric nonlinearity in the analysis in order to obtain more accurate results. In the present study, a computer program based on the iterative procedure has been developed for the three dimensional analysis of reinforced concrete frames with cracked beam and column elements. Probability-based effective stiffness model is used for the effective flexural stiffness of a cracked member. In the analysis, the geometric nonlinearity due to the interaction of axial force and bending moment and the displacements of joints are also taken into account. The analytical procedure has been demonstrated through the application of R/C frame examples in which its accuracy and efficiency in comparison with experimental and other analytical results are verified. The effectiveness of the analytical procedure is also illustrated through a practical four story R/C frame example. The iterative procedure provides equally good and consistent prediction of lateral deflection and effective flexural member stiffness. The proposed analytical procedure is efficient from the viewpoints of computational effort and convergence rate.