• Geomechanics and Engineering
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• v.11 no.3
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• pp.421-438
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• 2016

Explosions inside transportation tunnels might result in failure of tunnel structures. This study investigated the failure mechanisms of circular cast-iron tunnels in saturated soil subjected to medium internal blast loading. This issue is crucial to tunnel safety as many transportation tunnels run through saturated soils. At the same time blast loading on saturated soils may induce residual excess pore pressure, which may result in soil liquefaction. A series of numerical simulations were carried out using Finite Element program LS-DYNA. The effect of soil liquefaction was simulated by the Federal Highway soil model. It was found that the failure modes of tunnel lining were differed with different levels of blast loading. The damage and failure of the tunnel lining was progressive in nature and they occurred mainly during lining vibration when the main event of blast loading was over. Soil liquefaction may lead to more severe failure of tunnel lining. Soil deformation and soil liquefaction were determined by the coupling effects of lining damage, lining vibration, and blast loading. The damage of tunnel lining was a result of internal blast loading as well as dynamic interaction between tunnel lining and saturated soil, and stress concentration induced by a ventilation shaft connected to the tunnel might result in more severe lining damage.

• Proceedings of the Korean Reliability Society Conference
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• 2000.11a
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• pp.387-395
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• 2000

Circular consecutive-k-out-of-n:F system when the failure of component is dependent is studied. We assume that the failure of a component in the system increase the failure rate of the survivor which is working just before the failed component. In this case, a mean time to failure (MTTF), a average failure number of the system, and the expected cost per unit time are obtained. Then the minimum number of consecutive failed components to cause system failure to minimize the expected cost per unit time is determined as searching paths to system failure. And various numerical examples are studied.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.193-204
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• 2019

Reliability analyses of sixteen domestic design cases of open cell caisson breakwaters against circular sliding failure were conducted in this study. For the reliability analyses, uncertainties of parameters of soils, mound, and concrete cap were assessed. Bishop simplified method was used to obtain load and resistance of open cell caisson breakwater for randomly generated open cell caisson breakwater. Sufficient number of Monte Carlo simulations were conducted for randomly generated open cell caisson breakwaters, and statistical analysis was conducted on loads and resistances collected from the large number of Monte Carlo simulations. Probability of failure produced from Monte Carlo simulation has a nonconvergence issue for very low probability of failure; therefore, First-Order Reliability Method (FORM) was conducted using the statistical characteristics of loads and resistances of open cell caisson breakwaters. In addition, effects of safety factor, uncertainties of load and resistance, and correlation between load and resistance on reliability of open cell caisson breakwaters against circular sliding failure were examined.

• Geomechanics and Engineering
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• v.20 no.5
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• pp.461-474
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• 2020

Analysing the incompatible deformation and damage evolution around the tunnels in mixed strata is significant for evaluating the tunnel stability, as well as the interaction between the support system and the surrounding rock mass. To investigate this issue, confined compression tests were conducted on upper-soft and lower-hard strata specimens containing a circular hole using a rock testing system, the physical mechanical properties were then investigated. Then, the incompatible deformation and failure modes of the specimens were analysed based on the digital speckle correlation method (DSCM) and Acoustic Emission (AE) data. Finally, numerical simulations were conducted to explore the damage evolution of the mixed strata. The results indicate that at low inclination angles, the deformation and v-shaped notches inside the hole are controlled by the structure plane. Progressive spalling failure occurs at the sidewalls along the structure plane in soft rock. But the transmission of the loading force between the soft rock and hard rock are different in local. At high inclination angles, v-shaped notches are approximately perpendicular to the structure plane, and the soft and hard rock bear common loads. Incompatible deformation between the soft rock and hard rock controls the failure process. At inclination angles of 0°, 30° and 90°, incompatible deformations are closely related to rock damage. At 60°, incompatible deformations and rock damage are discordant due that the soft rock and hard rock alternately bears the major loads during the failure process. The failure trend and modes of the numerical results agree very well with those observed in the experimental results. As the inclination angles increase, the proportion of the shear or tensile damage exhibits a nonlinear increase or decrease, suggesting that the inclination angle of mixed strata may promote shear damage and restrain tensile damage.

• Geotechnical Engineering
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• v.12 no.6
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• pp.37-50
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• 1996

In this study, we collected data through the investigation of rock slopes of highway. By analyzing the collected data, the main factors of rock slope failure were studied. We studied on the failure types and scales according to rock types and geological structures in many rock slopes of highway. As a result, it was shown that many failed slopes were distributed in the areas of Cretaceous sedimentary rocks of south-eastern part in the Korean Peninsula and the Gneiss Complex in both Kyonggi-Do and Kangwon-Do. According to rock types, the following slope failure types were shown : that igneous rocks had the types of rock fall, plane failure, soil erosion and circular failure but had low failure frequency, and sedimentary rocks had predominantly the type of plane failure. Metamorphic rock showed the types of circular failure, wedge failure and plane failure due to poor rock qualities . According to geological structures, the following slope failure types were shown slope failure in igneous rocks was caused by joints, and in sedimentary rocks by bedding plane, and in metamorphic rocks by faults and poor rock qualities.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.09a
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• pp.280-287
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• 2003

The bridge columns with lap-splice reinforcements in earthquake suffered a brittle bond-slip failure due to the deterioration of lap-spliced longitudinal reinforcement without developing its flexural capacity or ductility. In this case, such a brittle failure can be controlled by the seismic retrofit using FRP wrapping. The retrofitted columns using FRP laminated circular tube showed significant improvement in seismic performance due to FRP's confinement effect. This paper presents the circumferential confinement effect of existing circular bridge pier strengthened with FRP wrapping for poor lap-splice details. The effects on the confinement of FRP wrapping, such as gap lengths between footing and FRP, fiber orientations, and thicknesses of FRP, were investigated by Quasi-static experiments.

• Steel and Composite Structures
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• v.18 no.3
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• pp.739-756
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• 2015

This paper presents investigations on the hysteretic behavior of concrete-filled circular tubular (CFCT) T-joints subjected to axial cyclic loading at brace end. In the experimental study, four specimens are fabricated and tested. The chord members of the tested specimens are filled with concrete along their full length and the braces are hollow section. Failure modes and load-displacement hysteretic curves of all the specimens obtained from experimental tests are given and discussed. Some indicators, in terms of stiffness deterioration, strength deterioration, ductility and energy dissipation, are analyzed to assess the seismic performance of CFCT joints. Test results indicate that the failures are primarily caused by crack cutting through the chord wall, convex deformation on the chord surface near brace/chord intersection and crushing of the core concrete. Hysteretic curves of all the specimens are plump, and no obvious pinching phenomenon is found. The energy dissipation result shows that the inelastic deformation is the main energy dissipation mechanism. It is also found from experimental results that the CFCT joints show clear and steady stiffness deterioration with the increase of displacement after yielding. However, all the specimens do not perform significant strength deterioration before failure. The effect of joint geometric parameters ${\beta}$ and ${\gamma}$ of the four specimens on hysteretic performance is also discussed.

• Smart Structures and Systems
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• v.18 no.3
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• pp.525-540
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• 2016

The CFRP-confined circular concrete-filled steel tubular column is composed of concrete, steel, and CFRP. Its failure mechanics are complex. The most important difficulties are lack of an available method to establish a relationship between a specific damage mechanism and its acoustic emission (AE) characteristic parameter. In this study, AE technique was used to monitor the evolution of damage in CFRP-confined circular concrete-filled steel tubular columns. A fuzzy c-means method was developed to determine the relationship between the AE signal and failure mechanisms. Cluster analysis results indicate that the main AE sources include five types: matrix cracking, debonding, fiber fracture, steel buckling, and concrete crushing. This technology can not only totally separate five types of damage sources, but also make it easier to judge the damage evolution process. Furthermore, typical damage waveforms were analyzed through wavelet analysis based on the cluster results, and the damage modes were determined according to the frequency distribution of AE signals.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.90-93
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• 2002

In view of reliability assessment, the failure mode analysis by performance tests for machine totals is researched in this study. First, the error analysis with circular movement test data is studied. The various errors and their origins are analyzed by error equations and related parts are investigated. Second, This paper deals with analysis of vibration testing fur machine tools spindle. The various frequency components are classified by FFT and order analysis. The simple measuring devices and error evaluation programs for tests are also developed.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.93-96
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• 2005

Since the columns with flexure-shear failure have lower ductility than those with flexural failure, shear capacity curve models shall be applied as well as flexural capacity curve in order to determine ultimate displacement for seismic design or performance evaluation. In this paper, a modified shear capacity curve model is proposed and compared with the other models such as the CALTRANS model, Aschheim et al.'s model, and Priestley et al.'s model. Four shear capacity curve models are applied to the 4 full scale circular bridge column test results and the accuracy of each model is discussed. It may not be fully adequate to drive a final decision from the application to the limited number of test results, however the proposed model provides the better prediction of failure mode and ultimate displacement than the other models for the selected column test results.