• Journal of the Korean Geotechnical Society
• /
• v.36 no.12
• /
• pp.125-132
• /
• 2020

Embedded joints in the rock mass are a major constituent influencing its mechanical behavior. Numerical analysis requires a rigorous modeling methodology for the rock mass with detailed information regarding joint properties, orientation, spacing, and persistence. This paper provides a mechanical model for a jointed rock mass based on the implicit joint-continuum approach. Stiffness tensors for rock mass are evaluated for an assemblage of intact rock separated by sets of joint planes. It is a linear summation of compliance of each joint sets and intact rock in the serial stiffness system. In the application example, kinematic analysis for a planar failure of rock slope is comparable with empirical daylight envelope and its lateral limits. Since the developed implicit joint-continuity model is formulated on a continuum basis, it will be a major tool for the numerical simulations adopting published plenteous thermal-hydro-chemical experimental results.

• Korean Journal of Metals and Materials
• /
• v.49 no.2
• /
• pp.112-120
• /
• 2011

The out-of-phase thermo-mechanical fatigue (OP TMF) in a <001> oriented single crystal nickel-based superalloy CMSX-4 has been studied. OP TMF life was less than a half of low cycle fatigue(LCF) life in spite of a small hysteresis loop area of OP TMF compared to that of LCF. The failure was caused by the initiation of a crack at the oxide-layered surface followed by its planar growth along the <100> ${\gamma}$ channel in both LCF and OP TMF. However, deformation twins appeared near the major crack of OP TMF. The multiple groups of parallel twin plates on {111} planes provided a preferential path for crack propagation, which caused a significant decrease in OP TMF life. Additionally, the analysis on the surface crack morphology revealed that the tensile strain at the minimum temperature of OP TMF was found to accelerate the crack propagation.

• Economic and Environmental Geology
• /
• v.41 no.6
• /
• pp.763-771
• /
• 2008

Uncertainties are pervasive in engineering geological problems. Therefore, the presence of uncertainties and their significance in analysis and design of slopes have been recognized. Since the uncertainties cannot be taken into account by the conventional deterministic approaches in slope stability analysis, the probabilistic analysis has been considered as the primary tool for representing uncertainties in mathematical models. However, some uncertainties are caused by incomplete information due to lack of information, and those uncertainties cannot be handled appropriately by the probabilistic approach. For those uncertainties, the theory of fuzzy sets is more appropriate. Therefore, in this study, fuzzy reliability analysis has been proposed in order to deal with the uncertainties which cannot be quantified in the probabilistic analysis due to the limited information. For the practical example, a slope is selected in this study and both the probabilistic analysis and the fuzzy reliability analysis have been carried out for planar failure. In the fuzzy reliability analysis, the dip angle and internal friction angle of discontinuity are considered as triangular fuzzy numbers since the random properties of the variables cannot be obtained completely under the conditions of limited information. In the study, the fuzzy reliability index and the probabilities of failure are evaluated from fuzzy arithmetic and compared to those from the probabilistic approach using Monte Carlo simulation and point estimate method. The analysis results show that the fuzzy reliability analysis is more appropriate for the condition that the uncertainties arise due to incomplete information.

• The Journal of the Convergence on Culture Technology
• /
• v.8 no.1
• /
• pp.507-512
• /
• 2022

The subjects of the study are the sedimentary rock slope of the Mesozoic Gyeongsang Supergroup, which has a high risk of failure. The rocks of the slope shall be sandstone, siltstone and dacite, and discontinuities shall develop beddings, shear joints, extension joints, and dacite dyke boundary planes. The type and scale of failure varies depending on the type of rock and the strike/dip of the discontinuities, but the planar failure prevails. Based on the face-mapping data, SMR, physical and mechanical testing of rocks, the critical equilibrium analysis, all representative sections required a countermeasure method because the acceptable safety factor during dry and rainy seasons were far below Fs=1.5 and Fs=1.2. After applying the countermeasure method, both the dry and wet conditions of the slope exceeded the allowable safety factor. In particular, the face-mapping data of the slope-face, the geological cross-sections of several representative sections perpendicular to the slope-face, and the critical equilibrium analysis and the presentation of countermeasure methods that have been reviewed based on them are expected to be reasonable tools for the slope stability.

• International Journal of Concrete Structures and Materials
• /
• v.8 no.2
• /
• pp.141-155
• /
• 2014

The use of fiber reinforced polymer (FRP) composites in strengthening reinforced concrete beam-column subassemblies has been scrutinised both experimentally and numerically in recent years. While a multitude of numerical models are available, and many match the experimental results reasonably well, there are not many studies that have looked at the efficiency of different finite elements in a comparative way in order to clearly identify the best practice when it comes to modelling FRP for strengthening. The present study aims at investigating this within the context of FRP retrofitted reinforced concrete beam-column subassemblies. Two programs are used side by side; ANSYS and VecTor2. Results of the finite element modeling using these two programs are compared with a recent experimental study. Different failure and yield criteria along with different element types are implemented and a useful technique, which can reduce the number of elements considerably, is successfully employed for modeling planar structures subjected to in-plane loading in ANSYS. Comparison of the results shows that there is good agreement between ANSYS and VecTor2 results in monotonic loading. However, unlike VecTor2 program, implicit version of ANSYS program is not able to properly model the cyclic behavior of the modeled subassemblies. The paper will be useful to those who wish to study FRP strengthening applications numerically as it provides an insight into the choice of the elements and the methods of modeling to achieve desired accuracy and numerical stability, a matter not so clearly explored in the past in any of the published literature.

• The Korean Journal of Nuclear Medicine
• /
• v.38 no.5
• /
• pp.331-337
• /
• 2004

Cardiac neurotransmission imaging allows in vivo assessment of presynaptic reuptake, neurotransmitter storage and postsynaptic receptors. Among the various neurotransmitter, I-123 MIBG is most available and relatively well-established. Metaiodobenzylguanidine (MIBG) is an analogue of the false neurotransmitter guanethidine. It is taken up to adrenergic neurons by uptake-1 mechanism as same as norepinephrine. As tagged with I-123, it can be used to image sympathetic function in various organs including heart with planar or SPECT techniques. I-123 MIBG imaging has a unique advantage to evaluate myocardial neuronal activity in which the heart has no significant structural abnormality or even no functional derangement measured with other conventional examination. In patients with cardiomyopathy and heart failure, this imaging has most sensitive technique to predict prognosis and treatment response of betablocker or ACE inhibitor. In diabetic patients, it allow very early detection of autonomic neuropathy. In patients with dangerous arrhythmia such as ventricular tachycardia or fibrillation, MIBG imaging may be only an abnormal result among various exams. In patients with ischemic heart disease, sympathetic derangement may be used as the method of risk stratification. In heart transplanted patients, sympathetic reinnervation is well evaluated. Adriamycin-induced cardiotoxicity is detected earlier than ventricular dysfunction with sympathetic dysfunction. Neurodegenerative disorder such as Parkinson's disease or dementia with Lewy bodies has also cardiac sympathetic dysfunction. Noninvasive assessment of cardiac sympathetic nerve activity with I-123 MIBG imaging nay be improve understanding of the pathophysiology of cardiac disease and make a contribution to predict survival and therapy efficacy.

• Journal of Sensor Science and Technology
• /
• v.14 no.6
• /
• pp.374-380
• /
• 2005

Vibration sensors have a wide scope of applications in the field of monitoring systems that needs to perceive an undesirable physical vibration before a critical failure occurs in a system, and then costly unplanned repairs can be avoided. The conventional vibration sensors developed so far have many disadvantages, such as complex manufacturing process, bulkiness, high cost, less reliability and so on. This paper reports a simple-structured vibration sensor, which has been developed using a commercialized conductive ball and silicon bulk-micromachining technology. The sensor consists of a conductive ball placed in $600{\mu}m$-deep micromachined silicon groove, in which Au thin film has been patterned using a shadow mask technique. Prior to the formation of the Au thin film, the sharp convex corner was rounded for smooth meatl deposition on the non-planar surface at the edge of the groove. The measurement results of the fabricated vibration sensor demonstrate a stable response characteristic to low-frequency vibration range ($1{\sim}30{\;}Hz$).

• Computers and Concrete
• /
• v.5 no.3
• /
• pp.217-241
• /
• 2008

In this paper, a total strain-based hysteretic material model based on MCFT is proposed for non-linear finite element analysis of reinforced concrete structures. Although many concrete models have been proposed for simulating behavior of structures under cyclic loading conditions, accurate simulations remain challenging due to uncertainties in materials, pitfalls of crude assumptions of existing models, and limited understanding of failure mechanisms. The proposed model is equipped with a fully generalized hysteresis rule and is formulated for 2D plane stress non-linear finite element analysis. The proposed model has been formulated in a tangent stiffness-based finite element scheme so that it can be used for most general finite element analysis packages. Moreover, it eliminates the need to check that tensile stresses can be transmitted across a crack. The tension stiffening model is a function of the bar orientation and any orientation can be accommodated. The proposed model has been verified with a series of experimental results of 2D RC planar panels. This study also demonstrates how parameters of the proposed model associated with cyclic damage modeling influences the pinched cyclic shear behavior.

• Geomechanics and Engineering
• /
• v.23 no.4
• /
• pp.301-311
• /
• 2020

In this study, shear strength behavior of fine-grained soils was investigated under unsaturated conditions. The samples in the unsaturated state were subjected to a net normal stress (σ-u_a) of 40 kPa and different matric suctions (u_a-u_w) of 50, 100 and 150 kPa. The matric suction values applied in the triaxial tests were selected according to the bubbling pressures determined from the SWC curves. The study was carried out on prepared re-constituted cylindrical samples by uniaxial consolidation of soil slurries. First, consolidated drained (CD) triaxial compression tests were performed on the saturated samples and the cohesion and angle of internal friction were determined. After that, drained triaxial compression tests under matric suctions were performed on the unsaturated samples. In order to obtain unsaturated test results, cohesion and internal friction angle values of saturated samples were used. The nonlinear surface representing the shear strength surface was approximated consisting of two planes (double planar surface). The reason for the nonlinear behavior of some soils is that the amount of sand content contained in it is relatively high and the bubbling pressure/permanent water content value is relatively low.

• Earthquakes and Structures
• /
• v.14 no.6
• /
• pp.505-523
• /
• 2018

Static pushover analyses of typical existing reinforced concrete frames, designed according to the previous generations of design codes in Greece, have established these structures' inelastic characteristics, namely overstrength, global ductility capacity and available behaviour factor q, under planar response. These were compared with the corresponding demands at the collapse limit state target performance point. The building stock considered accounted for the typical variability, among different generations of constructed buildings in Greece, in the form, the seismic design code in effect and the material characteristics. These static pushover analyses are extended, in the present study, in the time history domain. Consequently, the static analysis predictions are compared with Incremental Dynamic Analysis results herein, using a large number of spectrum compatible recorded base excitations of recent destructive earthquakes in Greece and abroad, following, for comparison, similar conventional limiting failure criteria as before. It is shown that the buildings constructed in the 70s exhibit the least desirable behaviour, followed by the buildings constructed in the 60s. As the seismic codes evolved, there is a notable improvement for buildings of the 80s, when the seismic code introduced end member confinement and the requirement for a joint capacity criterion. Finally, buildings of the 90s, designed to modern codes exhibit an exceptionally good performance, as expected by the compliance of this code to currently enforced seismic provisions worldwide.