• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.34 no.1
• /
• pp.175-183
• /
• 2014

This study investigates the response of structures to tunnelling-induced ground movements in clay ground, varying tunnel excavation condition (tunnel depth and diameter), tunnel construction condition (ground loss), and tunnel ground condition (soft clay and stiff clay). Four-story block-bearing structures have been used because the structures can easily be characterized of the extent of damages with crack size and distribution. Numerical parametric studies have been used to investigate of the response of structures to varying tunnelling conditions. Numerical analysis has been conducted using Discrete Element Method (DEM) to have real cracks when the shear and tensile stress exceed the maximum shear and tensile strength. The results of structure responses from various parametric studies have been integrated to consider tunnel excavation condition, tunnel construction condition, and tunnel ground condition and provide a relationship chart among them. Using the chart, the response of structures to tunnelling can easily be evaluated in practice in clay ground.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.11
• /
• pp.2305-2311
• /
• 2002

The pressure tube is a major component of the CANDU reactor, which supports nuclear fuel bundle and heavy water coolant. Pressure tubes are installed horizontally inside the reactor and only selected samples are periodically examined during in-service inspection. In this respect, a probabilistic safety assessment method is more appropriate fur the assessment of overall pressure tube safety. The failure behavior of CANDU pressure tubes, however, is governed by delayed hydride cracking which is the major difference from pipings and reactor pressure vessels. Since the delayed hydride cracking has more widely distributed governing parameters, it is impossible to apply a general PFM methodology directly. In this paper, a PFM methodology for the safety assessment of CANDU pressure tubes is introduced by applying Monte Carlo simulation in determining failure probability Initial hydrogen concentration, flaw shape and depth, axial and radial crack growth rate and fracture toughness were considered as probabilistic variables. Parametric study has been done under the base of pressure tube dimension and hydride precipitation temperature in calculating failure probability. Unstable fracture and plastic collapse are used for the failure assessment. The estimated failure probability showed about three-order difference with changing dimensions of pressure tube.

• Journal of Welding and Joining
• /
• v.35 no.2
• /
• pp.58-62
• /
• 2017

A319 aluminum alloy containing 6.5% Si and 3.5% Cu as major alloying elements has been widely used in machinery parts because of its excellent castability and crack resistance. However it needs more wear resistance to extend its usage to the severe wear environments. It has been known that hyper-eutectic Al-Si alloy having more than 12.6% Si contains pro-eutectic Si particles, which give better wear resistance and lubrication characteristics than hypo-eutectic Al-Si alloy like A319 alloy. In this study, it was tried to clad hyper-eutectic Al-Si alloy on the surface of A319 alloy. In the experiments, Al-36%Si alloy powder was mixed with organic binder to make a fluidic paste. The paste was screen-printed on the A319 alloy surface, melted by pulsed Nd:YAG laser and alloyed with the A319 base alloy. As experimental parameters, the average laser power was changed to 111 W, 202 W and 280 W. With increasing the average laser power, the melting depth was changed to $142{\mu}m$, $205{\mu}m$ and $245{\mu}m$, and the dilution rate to 67.2 %, 72.4 % and 75.7 %, and the Si content in the cladding layer to 16.2 %, 14.6 % and 13.7 %, respectively. The cross-section of the cladding layer showed very fine eutectic microstructure even though it was hyper-eutectic Al-Si alloy. This seems to be due to the rapid solidification of the melted spot by single laser pulse. The average hardness for the three cladding layers was HV175, which was much higher than HV96 of A319 base alloy. From the block-on-roll wear tests, A319 alloy had a wear loss of 5.8 mg, but the three cladding layers had an average wear loss of 3.5 mg, which meant that an increase of 40 % in wear resistance was obtained by laser cladding.

• The Journal of Engineering Geology
• /
• v.28 no.3
• /
• pp.455-463
• /
• 2018

This study developed a method to quantitatively measure the size of cracks in concrete using X-ray CT images. We prepared samples with a diameter of 50 mm and a length of 100 mm by coring cracked concrete block that was obtained by chipping. We used a micro-focus X-ray CT, then applied the 3DMA method (3 Dimensional Medial axis Analysis) to the 3D CT images to find effective parameters for damage assessment. Finally, we quantitatively assessed the damage based on sample locations, using the damage assessment parameter. Results clearly show that the area near the chipping surface was damaged to a depth of 3 cm. Furthermore, X-ray methods can be used to evaluate the porosity index, burn number, and medial axis, which are used to estimate the damage to the area near the chipping surface.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.57-60
• /
• 2008

Compared with a steel-reinforced section with equal areas of longitudinal reinforcement, a cross section using FRP flexural reinforcement after cracking has a smaller depth to the neutral axis because of the lower axial stiffness. The compression region of the cross section is reduced, and the crack widths are wider. As a result, the shear resistance provided by both aggregate interlock and compressed concrete is smaller. Research on the shear capacity of flexural members without shear reinforcement has indicated that the concrete shear strength is influenced by the stiffness of the flexural reinforcement. In this research, experimental observations were made for the shear strength of FRP reinforced concrete beam and validity of existing predicting equations were examined. Test results showed that shear strength decreased as shear-span increased.

• Journal of the Korea Concrete Institute
• /
• v.17 no.3 s.87
• /
• pp.445-454
• /
• 2005

Cracks due to low tensile strength in prestressed concrete (PC) beams may decrease rigidity and structural performance, resulting in excessive deflection. In an effort to solve this problem, in this research, prestressed dual concrete (PDC) has been proposed, consisting of normal strength concrete in compression zone, and high performance steel fiber reinforced concrete(HPSFRC) with a partial depth in tensile zone. Three PDC beams with different depths of HPSFRC and two PC beams were cast for experiments. Analytical models at each stage, i.e., precracking, postcracking, and ultimate, were proposed for analysis of flexural behavior in PDC beams. The experimental results agree well to the analytical ones. Crack formation and its propagation are controlled by the HPSFRC in PDC beams. The initial cracking and service limit loads are increased along with the load carrying capacity and flexural stiffness.

• Journal of the Korean Geosynthetics Society
• /
• v.17 no.4
• /
• pp.65-72
• /
• 2018

Seismically induced settlement exceeding dam freeboard may lead to a dam failure. The prediction of settlement is important also because it is also reported to be strongly related to longitudinal crack width and depth, which are critical indices used for safe evaluation of dams. The empirical correlation derived from numerical simulations is most often used. In this study, two-dimensional dynamic nonlinear analyses are performed using representative CFRD and ECRD fill dams. A total of 20 recorded motions are used to account for the influence on ground motion intensity and magnitude. The calculated crest settlements are correlated to four ground motion parameters, which are peak ground acceleration (PGA), peak ground velocity (PGV), Aria Intensity ($I_A$), and magnitude. It is demonstrated that using ground motion parameters in addition to PGA can significantly increase the prediction accuracy.

• The Journal of the Convergence on Culture Technology
• /
• v.10 no.2
• /
• pp.511-516
• /
• 2024

The recently enacted detailed guidelines on the performance evaluation of track facilities presented the necessary requirements regarding the evaluation procedures and implementation methods of track performance evaluation. However, the grade of rail surface damage is determined by external inspection (visual inspection), and there is no choice but to rely only on qualitative evaluation based on the subjective judgment of the inspector. Therefore, in this study, we attempted to develop a diagnostic application that can diagnose rail internal defects using rail surface damage. In the field investigation, rail surface damage was investigated and patterns were analyzed. Additionally, in the indoor test, SEM testing was used to construct image data of rail internal damage, and crack length, depth, and angle were quantified. In this study, a deep learning model (Fast R-CNN) using image data constructed from field surveys and indoor tests was applied to the application. A rail surface damage diagnosis application (App) using a deep learning model that can be used on smart devices was developed. We developed a smart diagnosis system for rail surface damage that can be used in future track diagnosis and performance evaluation work.

• Nuclear Engineering and Technology
• /
• v.27 no.2
• /
• pp.226-233
• /
• 1995

The wall thickness of a pressure tube is increased in order to reduce the probability of failure in a pressure tube of CANDU type reactor. It is presented here that the variation of wall thickness changes stress, hydrogen concentration and delayed hydride cracking in Zr-2.5Nb pressure tube. When the wall thickness is increased from 4.2 mm to 5.2 mm, the stress exerted on the tube and the deuterium taken up during operation are reduced by 19％. Further, the calculated allowable depth of the surface flaw over which delayed hydride cracking(DHC) is susceptible increases by 50％. DHC initiation is controlled by the stress and by the hydrogen concentration in the pressure tube. The results are therefore very significant in such a respect that increased wall thickness may reduce DHC initiation. Ac the wall thickness increases the hydrostatic tension will increase. Its impact on the acceleration of the crack growth rate of DHC deserves further studies.

• Journal of the Korean Geotechnical Society
• /
• v.15 no.6
• /
• pp.219-238
• /
• 1999

In the present study, laboratory tests including the seepage-induced consolidation test, suction test, and desiccation shrinkage test are performed to investigate characteristics of the desiccation shrinkage in reclaimed hydraulic fills. Soil samples for laboratory tests are obtained from three sites (districts of Haenam, Kogeum and Koheung in Chunnam area). Desiccation shrinkage settlement caused by three dimensional volume change is numerically evaluated using finite difference technique based on the governing equation proposed by Abu-Hejleh & Znidarcic. Also characteristics of the desiccation shrinkage analyzed from the test results are used as input data for numerical evaluations. Further predicted total settlements including the self-weight consolidation settlement are compared with values measured at the site of Haenam district. Finally, effects of parameters related to the desiccation shrinkage on settlements are examined.