• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.841-846
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• 2002

Development on non-destructive testing methods were performed to evaluate the effectiveness of crack repair for test beams induced a crack. Cracked beams are repaired with expoxy and microcement, and then they are tested by two methods, the ultrasonic pulse velocity method and the transfer function method. It is proved that the ultrasonic pulse velocity method is very valid for the evaluation of the effectiveness on expoxy repair, and the transfer function method is very applicable to evaluate the effectiveness on microcement repair.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.267-272
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• 2000

The modeling on uplift pressure on the foundation of a dam on which it was constructed, and on the interface between the dam and foundation is a critical aspect in the analysis of concrete gravity dams. The evaluation of stress intensity factor at the crack tip of concrete gravity dam due to uplift pressure effect by surface integral method is performed in this study. The effects of body force, overtopping pressure and water pressure on the crack-face are also considered in this study.

• Journal of the Korean Society of Safety
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• v.6 no.3
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• pp.50-55
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• 1991

It is well known that mechanisms of fracture and crack growth depend upon material characteristics such as fracture toughness, environmental condition, cracd geometry and mechanical properties. It seems to be very important to investihate the effects of the above factors on the behavior of structural components which contain flaws for the detailed evaluation of their intehrity. In this experimental research, fracture behaviors of moterials were investigated by using Acoustic Emission(AE) technique. The fracturing processes of materials were estimated through both the tension specimens. For the detrmlnatlon of yied strength or fracture toughness, the critical applied load at the crack initiation and propagation is thought to be very important. The critical applied load(PQ) was determined through AE signal. The source of AE signal was estimated by fractography analysis. These experimental results may contribute to the safety analyses and the evaluation of strength of structures.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.3
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• pp.215-221
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• 2005

It is required to evaluate nondestructively depth of surface-breaking cracks in structures. In this paper, the self-compensated technique by laser-based ultrasound is used to measure the depth of surface-breaking defect. Optical generation of ultrasound produces a well defined pulse with reliable frequency content. It is broad banded and suitable for measurement of attenuation and scattering over a wide frequency range. The self-calibrated signal transmission data of surface wave shows good sensitivity as a practical tool far assessment of surface-breaking defect depth. It is suggested that the relationship between the signal transmission and crack depth can be used to predict the surface-breaking crack depths in structures.

• Journal of the Korean Society for Precision Engineering
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• v.7 no.4
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• pp.130-139
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• 1990

It is well known that mechanisms of fracture and crack growth depend upon material characteristics such as fracture toughness, environmental condition, crack geometry and mechanical properties. It seems to be very important to investighate the effects of the above factors on the behavior of structural components which contain flaws for the detailed evaluation of their integrity. In this experimental research, fracture behaviors of SK-5 high carbon steel was investigated by using Acoustic Emission(AE) technique. Fracturing processes of materials were estimated through both the tension test with nominal specimens and the fracture test with compact tension specimens. The critical applied load which corresponds to the crack initiation and propagation is very improtant for the determination of yield strength of fracture toughness. The critical applied load($P_Q$) was determined through AE method and the source of AE signal was estimated by fractography analysis. The experimental results may contribute to the safety analyses and strength evaluation of structures.

• Journal of the Korean Society of Safety
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• v.15 no.2
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• pp.46-50
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• 2000

A theoretical model for the evaluation of small surface fatigue crack initiated from a pit-type surface flaw is presented. The low frequency scattering model is developed based on the reciprocity principle for the elastic wave scattering. The effect of the flaw on the surface wave reflection from the crack is taken into account approximately by means of the stress intensity factor of cracks on a through thickness hole. The reflection coefficient of surface wave is derived for the prediction of small surface crack depth. Calculated results for pits with different sizes are illustrated.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.67-72
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• 2000

Demand for now nondestructive evaluation are growing to detect fatigue crack growth behavior to predict long term performance of materials and structure in aggressive environments especially when they are In non-visible area. Acoustic emission technique is well suited to these problems and has drawn a keen interests because of its dynamic detection ability, extreme sensitivity and location of growing defects. In this study, we analysed acoustic emission signals obtained in fatigue and tensile test of high strength fire resistance steel for frame structure with time-frequency analysis methods. The main frequency range is different in the noise and the fatigue crack propagation. It could be classified that it were also generated by composite fracture mechanics of cleavage, dimple, inclusion separation etc.

• Proceedings of the KSR Conference
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• 1998.11a
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• pp.87-95
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• 1998

This study proposes the analysis and evaluation method of time series ultrasonic signal using the attractor analysis. Features extracted from time series signal analyze quantitatively characteristics of welding defects. For this purpose, analysis objective in this study is fractal dimension and attractor Quadrant feature. Trajectory changes in the attractor indicated that even the same type of defects carried substantial difference in fractal characteristics resulting from distance shifts such as parts of head and flange. Such differences in characteristics of weld defects enables the evaluation of unique features of defects in the weld zone. In quantitative fractal feature extraction, feature values of 3.848 in the case of part of head(crack) and 4.102 in the case of part of web(side hale) and 3.711 in the case of part of flange(crack) were proposed on the basis of fractal dimensions. Proposed attractor feature extraction in this study can enhance the precision rate of ultrasonic evalaution for defect signals of rail weld zone such as side hole and crack.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.5
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• pp.41-50
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• 2009

Following an earthquake, the major concerns for damaged buildings are their safety/risk in the event of aftershocks, and thus a quantitative damage assessment must be performed in order to evaluate their residual seismic capacity and to identify necessary actions for the damaged buildings. Post-event damage evaluation is therefore as essential for the quick recovery of a damaged community as pre-event seismic evaluation and strengthening of vulnerable buildings. The objective of this study is to develop a post-earthquake seismic evaluation method for RC frames with URM infill wall for typical school buildings. For this purpose, full-scale, one-bay, single-story specimens having different axial loads in columns are tested under cyclic loadings. During the tests, residual crack widths, which can also be found in damaged buildings, are measured in order to estimate the residual seismic capacity from the observed damage. In this paper, the relationship between the measured residual crack width and the residual seismic capacity is discussed analytically and experimentally, and reduction factors are proposed to estimate the residual seismic capacity based on the observed damage level.

• International Journal of Highway Engineering
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• v.19 no.2
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• pp.103-112
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• 2017

PURPOSES : In this study, field performance evaluation of crack treatment of pavement and the feasibility of surface treatment of pavement are presented. The performance and cost of preventive maintenance methods have been previously verified, and the methods are being used in many developed countries and cities. However, the performance and cost of the system have not been verified in domestic, field applications. Therefore, in order to improve performance, the field performance is evaluated, and a reasonable cost is proposed. METHODS : Visual Inspection was conducted to evaluate the field application and performance of the preventive maintenance method. In addition, the PCI index was calculated from the results of visual inspection of the application area of the surface treatment method, and the performance life of each method was predicted. For the economic evaluation, life cycle cost analysis was performed using the life cycle cost analysis program. RESULTS :In order to evaluate and quantify the field performance of crack repair material, the residue condition of the pavement surface after crack treatment, rather than the performance of the material, is evaluated. In addition, the crack resistance and performance life of surface treatment methods are evaluated. The cost of currently available treatment methods are compared to the common pavement cut and overlay method, and it is determined that the preventive method is not economical based on life cycle cost analysis. CONCLUSIONS :Because of the characteristics of cracking, it is necessary to conduct the evaluation of currently applied methods and the analysis of the cause of damage, by visual inspection. Moreover, in order to evaluate the performance and economic suitability of the currently applied surface treatment methods, it is necessary to acquire information on application sections by monitoring their long-term conditions and performance.