• Proceedings of the Korea Concrete Institute Conference
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• 2000.10b
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• pp.1291-1296
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• 2000

A basis for the direct use of data from nondestructive evaluation methods in bridge management systems is presented. Bridge management systems use integer-valued condition ratings to recognize conditions of bridge elements, to model progression of deterioration, and to determine repair needs. Data from nondestructive evaluation methods can inform management systems on the extent of damage, on the initiation of deterioration processes, and on the exposure of bridge elements to aggressive agents. In addition, data obtained through nondestructive evaluation methods allow the formation of models of specific deterioration process. The use of these data in bridge management systems requires redefinition of condition ratings together with the creation of procedures for automated interpretation of data. By these action, nondestructive evaluation methods are directly used to assign condition ratings, and condition ratings are made into terse form of NDE data that are compatible with present day bridge management systems. This paper reports work in progress to strategic use of nondestructive evaluation methods in bridge management system.

• Geomechanics and Engineering
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• v.30 no.5
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• pp.401-411
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• 2022

To obtain the dynamic mechanical properties, fracture modes, energy and brittleness characteristics of Furong Baijiao coal rock, the dynamic impact compression tests under 0, 4, 8 and 12 MPa confining pressure were carried out using the split Hopkinson pressure bar. The results show that failure mode of coal rock in uniaxial state is axial splitting failure, while it is mainly compression-shear failure with tensile failure in triaxial state. With strain rate and confining pressure increasing, compressive strength and peak strain increase, average fragmentation increases and fractal dimension decreases. Based on energy dissipation theory, the dissipated energy density of coal rock increases gradually with growing confining pressure, but it has little correlation with strain rate. Considering progressive destruction process of coal rock, damage variable was defined as the ratio of dissipated energy density to total absorbed energy density. The maximum damage rate was obtained by deriving damage variable to reflect its maximum failure severity, then a brittleness index BD was established based on the maximum damage rate. BD value declined gradually as confining pressure and strain rate increase, indicating the decrease of brittleness and destruction degree. When confining pressure rises to 12 MPa, brittleness index and average fragmentation gradually stabilize, which shows confining pressure growing cannot cause continuous damage. Finally, integrating dynamic deformation and destruction process of coal rock and according to its final failure characteristics under different confining pressures, BD value is used to classify the brittleness into four grades.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.11a
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• pp.233-239
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• 1999

The feasibility of an ultrasonic technique using a pulse-echo method of normal-incident compressional waves was evaluated for its sensitivity to the worn surface and near surface damage due to wear. Worn surfaces were generated at various oscillation frequency under a given load and amplitude and these surface were in situ monitored using a ultrasonic wave detection system. Analysis of the ultrasonic waves received from the worn surface revealed a close relationship between the surface and near-surface damage and the maximum echo-amplitude of the compressional waves. The ultrasonic technique was successful in assessing the level of severity of the worn surface in real time during the wear process. It is also shown that the wear depth can be easily measured by the calculation of change of the specimen thickness based on the wave speed measured for the specimen medium.

• Journal of the Korean Society of Safety
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• v.16 no.4
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• pp.47-51
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• 2001

The carbon fiber reinforced plastics(CFRP) have been widely used in aircraft and spacecraft structures as well as sports goods because it has high specific strength, high specific stiffness and low coefficient of thermal expansion. Machining of CFRP poses problems not frequently seen for metals due to the nonhomogeneity, anisotropy, and abrasive characteristics of CFRP. Delamination is a common problem faced while drilling holes in CFRP using conventional drilling. Therefore, AE characteristics related to drilling damage process of unidirectional and [0/90/]s crossply laminate composite was studied. Also drilling damage like the delamination was observed by video camera in real time monitoring technique. From the results, we basically found the relationships between the delamination from drilling and AE characteristics for CFRP composites.

• Tribology and Lubricants
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• v.16 no.5
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• pp.351-356
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• 2000

The feasibility of an ultrasonic technique using a pulse-echo method of normal-incident compressional waves was evaluated for its sensitivity to the worn surface and near surface damage due to wear. Worn surfaces were generated at various oscillation frequency under a given load and amplitude and these surface were in situ monitored using a ultrasonic wave detection system. Analysis of the ultrasonic waves received from the worn surface revealed a close relationship between the surface and near-surface damage and the maximum echo-amplitude of the compressional waves. The ultrasonic technique was successful in assessing the level of severity of the worn surface in real time during the wear process. It is also shown that the wear depth can be easily measured by the calculation of change of the specimen thickness based on the wave speed measured for the specimen medium.

• Journal of the Korea Concrete Institute
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• v.21 no.4
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• pp.457-464
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• 2009

Fiber is an important ingredient in fiber-reinforced cement composite (FRCC) which can control fracture of cement composite by bridging action. In compliance with the action of the fiber and the aggregate size, it also showed a different failure mechanism. For practical application, it is needed to investigate the fracture behavior of the FRCC and to understand the micro-mechanism of cement matrix with reinforcing fiber. In order to evaluate a characteristics of fracture process in the FRCC, acoustic emission (AE) technique was used for the analysis and evaluation of FRCC damage by acoustic emission under flexural and cyclic compressive loadings. The AE signals were monitored by AMSY4 AE instrument during the entire loading period. The specimens are reinforced with 0, 1.0, 1.5 and 2.0% (by volume) Polyvinyl alcohol (PVA) fiber. The test results showed that the damage progress of the FRCC was characteristic for the fiber replacement ratio. As a result of analyzing the felicity ratio (FR) values, it is shown that this values can be used for evaluating the degree of FRCC damage. On the whole the felicity ratio values of FRCC are shown between 0.4 and 1.1. And, the AE kaiser effect was shown in the all FRCC specimen. In addition, the damage behavior and the microscopic fracture process of the FRCC are evaluated using the AE parameters, such as calm ratio, b-value and felicity ratio. The purpose of this reserch was to advance the state of knowledge regarding the applicability of acoustic emission as an evaluation method for FRCC.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.9
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• pp.783-790
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• 2014

Railway wheels and axles are the most critical parts of the railway rolling stock. The wheel carry axle loads and guide the vehicles on the track. Therefore, the contact surface of wheel are subjected to wear and fatigue process. The wheel damage can be divided into three types; wear, contact fatigue failure and thermal crack due to braking. Therefore, in the contact surface between the wheel and the rail, the materials are heat treated to have a specific hardness. The manufacturing quality of the wheel have a considerable influence on the formation of tread wear and damage. Also, the residual stress on wheel is formed during the manufacturing process is one of the main sources of the damage. In this paper, the mechanical characteristic and the residual stress according to wheel material have been evaluated by applying finite element analysis and conducting mechanical tests.

• Journal of the Korean Society of Safety
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• v.30 no.6
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• pp.56-62
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• 2015

Recently, one of countermeasures against aging SOC infrastructures, performance-focused management including the serviceability, functionality, durability, and economics has been changed from the structural safety-focused evaluation has changed into The current inspection and diagnosis for the major SOC facilities in Korea has been carried out by the specific principle of details, and most of them checked by the visual inspection are focused on the repair and rehabilitation of the damaged structures, thus they are the preventive maintenance. However, the performance-focused management should be replaced for the effective and economic maintenance as wells as for the minimization of the damage. In this regard, this study the appropriacy of the current evaluation items about the concrete retaining wall, one of SOC infrastructures as the previous step forward the performance-focused management. In order to deduct the effective evaluation items in order, the entropy, analytic hierachy process (AHP), and promethee analysis were peformed and the results were compared and discussed.

• Journal of Urban Science
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• v.11 no.1
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• pp.9-13
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• 2022

Currently, RC slab bridges in use in Korea account for most of the total bridges, and bridges with a service life of 20 years or more account for about 75%. However, most of these RC slab bridges have a span of less than 20m and are not included in the first and second types of facilities, so maintenance is very neglected. Therefore, in this study, field load test is performed on an aged RC slab bridge, and the performance evaluation is performed based on the structural response results (deflection, impact coefficient, natural frequency, etc.) of the bridge obtained through field load test. In addition, the performance evaluation results obtained through the load test are intended to be used as basic data for the damage evaluation process of the bridge currently under development.

• Earthquakes and Structures
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• v.14 no.2
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• pp.155-165
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• 2018

Methods based on nonlinear static analysis as simple tools could be used for the seismic analysis and assessment of structures. In the present study, capability of the N2 method as a well-known nonlinear analysis procedure examines for the estimation of the damage index of multi-storey reinforced concrete frames. In the implemented framework, equivalent single-degree-of-freedom (SDOF) models are utilized for the global damage estimation of multi-degree-of-freedom (MDOF) systems. This method does not require high computational analysis and subsequently decreases the required time of seismic design and assessment process. To develop the methodology, RC frames with period range from 0.4 to 2.0 s under 40 records are studied. The effectiveness of proposed technique is evaluated through numerical study under near- and far-field earthquake ground motions. Finally, the results of developed models are compared with two other simplified schemes along with nonlinear time history analysis results of multi-storey frames. To improve the accuracy of damage estimation, a modified relation is presented based on the N2 method results for near- and far-field earthquakes.