• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.231-238
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• 2002

Dry shrinkage md temperature change cause to develope concrete bridge decks on main girders have initial unidirectional cracks in longitudinal or transverse direction. As they receive traffic loads, the crack gradually propagate in different directions depending on the concrete dimension and reinforcement ratio. Since existing equations that predict crack width are mostly based on the one directional bond-slip theory, it is difficult to determine the actual crack width of a bridge deck with varying the spacing of rebar or strengthening material and to estimate the improvement rate in serviceability of the strengthened bridge deck. In this study, crack propagation mechanism is identified based on the test results and a new crack prediction equation is proposed for evaluation of serviceability. Although more accurate results are derived using the proposed equation, the extent of error is increased as the strain of the rebar or the strengthening material increases after the yielding of rebar Therefore, further research is required to better predict the crack width after the rebar yields under fatigue loading condition.

• Journal of the Korea Institute of Military Science and Technology
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• v.2 no.1
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• pp.101-109
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• 1999

The objective of this research is to study effects of the residual stresses on the crack growth and the life of the structure, caused by cold working around the hole of the aircraft structure which will be jointed by rivets and bolts, etc. The compensated Morrow's equation, by experimental data from the materials AL7075-T6 and AL2024-T3, is suggested to calculate the values of the fatigue life prediction of the structure. Also, the compensated Forman's equation, by experimental data from a material AL7075-T6, is suggested to calculate the values of the crack growth prediction of the structure. It is founded that the calculated values from the suggested equations are almost close to the known values of the fatigue life prediction and the crack growth prediction. It is shown that this paper, associated with an initial research on the effects of residual stresses around hole, gives a direction to study the problem at the aircraft maintenance field.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.349-352
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• 2011

본 논문에서는 변동하중 하에서의 균열 성장 예측을 위하여 손상 모델과 주어진 데이터에 기반하여 균열 성장 모델의 변수를 확률분포로 추정한다. 이를 위해 베이지안 접근법을 활용하여 불확실 변수 결합 확률 분포식을 구축하고, Markov Chain Monte Carlo(MCMC)을 통해서 균열 성장 모델의 변수 샘플을 추출하였다. 여기서 추출된 샘플들을 균열 성장 모델에 적용, 균열 성장의 결과를 확률적인 분포로 예측하였다. 위와 같은 추정은 재료의 물성과 같은 변동성이 있는 변수를 모델에 적용하여, 결과값을 확률적인 분포로 예측하였다. 이것은 기존의 안전계수 개념보다 더욱 적절한 안전 기준을 제시 할 수 있다.

• Journal of the Korea Concrete Institute
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• v.18 no.4 s.94
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• pp.543-552
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• 2006

The current design for crack width control in concrete bridges is incomplete in analytical models. As one of the important serviceability limit states, the crack width be considered with the quantitative prediction of the initiation and propagation of corrosion and corrosion-induced cracking. A serviceability limit state of cracking can be affected by the combined effects of bond, slip, cracking, and corrosion of the reinforcing elements. Considering life span of concrete bridges, an improved prediction of crack width affected by time-dependent general corrosion has been proposed for the crack control design. The developed corrosion models and crack width prediction equation can be used for the design and the maintenance of prestressed and non-prestressed reinforcements by varying time, w/c, cover depth, and geometries of the sections. It can also be used as the rational criteria for the maintenance of existing concrete bridges and the prediction of remaining life of concrete structures.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.67-68
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• 2010

The bond stress and crack spacing are effected the calculated crackwidth. EC2 and MC90 suggest crackwidth function that maximum crack spacing and difference average strain. This study is predict crackwidth, according to each design standard than comprison and analyis test data. The result, each design standard ways are predict well to test data.

• Journal of the Korean Society of Safety
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• v.15 no.4
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• pp.163-169
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• 2000

This paper mainly deals with fatigue lift estimation and prediction in notched structures. The fatigue crack initiation life and the fatigue crack growth behavior in the DEN specimens were predicted using S.I.F. K solution derived in this study and the Paris' crack growth equation. Predicted results showed good agreement with experimental crack growth behaviors under constant-load-amplitude.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.617-623
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• 1990

Cracks present in pressure vessels have been reported to be mostly semi-elliptic surface cracks. The fatigue crack growth rates(FCGR) of surface cracks in the pressure vessel materials, API5A-K55 and SPV 500, used in this study were showed to be different depending on the direction of propagation of the surface crack. An equation for the prediction of the shape change of the surface crack was obtained by combining the Paris' relations for each direction of surface crack extension and agreed well with the experimental data. And also FGGR in both materials were evaluated and prediction of the shape change of surface crack were made using averaged stress intensity factor.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.3
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• pp.267-275
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• 2012

In this study, crack growth in a center-cracked plate is predicted under mode I variable amplitude loading, and the result is validated by experiment. Huang's model is employed to describe crack growth with acceleration and retardation due to the variable loading effect. Experiment is conducted with Al6016-T6 plate, in which the load is applied, and crack length is measured periodically. Particle Filter algorithm, which is based on the Bayesian approach, is used to estimate model parameters from the experimental data, and predict the crack growth of the future in the probabilistic way. The prediction is validated by the run-to-failure results, from which it is observed that the method predicts well the unique behavior of crack retardation and the more data are used, the closer prediction we get to the actual run-to-failure data.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.2
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• pp.193-202
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• 2018

This paper proposed a crack spacing calculation formulation which is an important parameter for calculating the crack width, that is the main factor for verification of serviceability limit states and durability performance evaluation of reinforced concrete members. The basic equation of average crack spacing is derived by considering the bond characteristics which is the governing equation for the analysis of cracking behavior in reinforced concrete members. In order to consider the effect of the cover thickness and concrete compressive strength, the crack spacing measured in 124 direct tensile tests performed by several researchers was analyzed and each coefficient was proposed. And, correlation analysis was performed from 80 specimen data where the maximum and average crack spacing were simultaneously measured, and a correlation coefficient that can easily predict the maximum crack spacing from the average crack spacing was proposed. The results of the proposed average crack spacing equation and maximum crack spacing correlation were compared with those current design code specification. The comparisons of proposed equations and the Korean design codes show that the proposed formulation for the average crack spacing and the maximum crack spacing improves the accuracy and reliability of prediction compared to the corresponding provisions of the Korean Concrete Structural Design Code and Korean Highway Bridge Design Code (Limit States Design).

• Explosives and Blasting
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• v.14 no.4
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• pp.13-19
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• 1996

Lately, the improtance of smooth blasting is increasing on every construction fields, suchas underground caves, tunnels, and roadconstruction, etc. The main purpose of smooth blasting is to prevent unnecessary cracks from the base rockwhich preserved permanently and is to gain the smooth fracture plane. So, in smooth blashing, explosives with low detonating velocity are generally used. But it is difficult to discuss general theory on the smooth blashing because the mechanical properties of pertienent rocks are difficult regionally. Accordingly basic reserches on the smooth blasting are demended. In this paper, the mechanisms of the smooth blasting on the rocks containing discontinuities were discussd. Firstly, the writer predicted the formation of fracture plane and unevenness using mathematical methodology, the next the model blast tests were conducted in order to simulate the crack propagation modes from the blast holes. Through the research, the following conclusions were obtained l)The blast test results were in reasonally good agreement with the theoretical prediction. 2)The degree of discontinuity has an influence on the fracture morphology.