• Steel and Composite Structures
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• 제29권1호
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• pp.1-22
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• 2018

Multi-storey precast concrete skeletal structures are assembled from individual prefabricated components which are erected on-site using various types of connections. In the current design of these structures, beam-to-column connections are assumed to be pin jointed. Welded plate beam to-column connections have been used in the precast concrete industry for many years. They have many advantages over other jointing methods in component production, quality control, transportation and assembly. However, there is at present limited information concerning their detailed structural behaviour under bending and shear loadings. The experimental work has involved the determination of moment-rotation relationships for semi-rigid precast concrete connections in full scale connection tests. The study reported in this paper was undertaken to clarify the behaviour of such connections under symmetrical vertical loadings. A series of full-scale tests was performed on sample column for which the column geometry and weld arrangements conformed with successful commercial practice. Proprietary hollow core slabs were tied to the beams by tensile reinforcing bars, which also provide the in-plane continuity across the connections. The strength of the connections in the double sided tests was at least 0.84 times the predicted moment of resistance of the composite beam and slab. The secant stiffness of the connections ranged from 0.7 to 3.9 times the flexural stiffness of the attached beam. When the connections were tested without the floor slabs and tie steel, the reduced strength and stiffness were approximately a third and half respectively. This remarkable contribution of the floor strength and stiffness to the flexural capacity of the joint is currently neglected in the design process for precast concrete frames. In general, the double sided connections were found to be more suited to a semi-rigid design approach than the single sided ones. The behaviour of double sided welded plate connection test results are presented in this paper. The behaviour of single sided welded plate connection test results is the subject of another paper.

• Geomechanics and Engineering
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• 제12권4호
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• pp.611-626
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• 2017

The research reported herein is concerned with the model testing of piles socketed in soft rock which was simulated by cement, plaster, sand, water and concrete hardening accelerator. Model tests on a single pile socketed in simulated soft rock under axial cyclic loading were conducted and the bearing capacity and accumulated deformation characteristics under different static, and cyclic loads were studied by using a device which combined oneself-designed test apparatus with a dynamic triaxial system. The accumulated deformation of the pile head, and the axial force, were measured by LVDT and strain gauges, respectively. Test results show that the static load ratio (SLR), cyclic load ratio (CLR), and the number of cycles affect the accumulated deformation, cyclic secant modulus of pile head, and ultimate bearing capacity. The accumulated deformation increases with increasing numbers of cycles, however, its rate of growth decreases and is asymptotic to zero. The cyclic secant modulus of pile head increases and then decreases with the growth in the number of cycles, and finally remains stable after 50 cycles. The ultimate bearing capacity of the pile is increased by about 30% because of the cyclic loading thereon, and the axial force is changed due to the applied cyclic shear stress. According to the test results, the development of accumulated settlement is analysed. Finally, an empirical formula for accumulated settlement, considering the effects of the number of cycles, the static load ratio, the cyclic load ratio and the uniaxial compressive strength, is proposed which can be used for feasibility studies or preliminary design of pile foundations on soft rock subjected to cyclic loading.

• Steel and Composite Structures
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• 제34권6호
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• pp.891-907
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• 2020

Many studies reveal that during destructive earthquakes, most of the structures enter the inelastic phase. The amount of hysteretic energy in a structure is considered as an important criterion in structure design and an important indicator for the degree of its damage or vulnerability. The hysteretic energy value wasted after the structure yields is the most important component of the energy equation that affects the structures system damage thereof. Controlling this value of energy leads to controlling the structure behavior. Here, for the first time, the hysteretic behavior and energy dissipation capacity are assessed at presence of elliptical braced resisting frames (ELBRFs), through an experimental study and numerical analysis of FEM. The ELBRFs are of lateral load systems, when located in the middle bay of the frame and connected properly to the beams and columns, in addition to improving the structural behavior, do not have the problem of architectural space in the bracing systems. The energy dissipation capacity is assessed in four frames of small single-story single-bay ELBRFs at ½ scale with different accessories, and compared with SMRF and X-bracing systems. The frames are analyzed through a nonlinear FEM and a quasi-static cyclic loading. The performance features here consist of hysteresis behavior, plasticity factor, energy dissipation, resistance and stiffness variation, shear strength and Von-Mises stress distribution. The test results indicate that the good behavior of the elliptical bracing resisting frame improves strength, stiffness, ductility and dissipated energy capacity in a significant manner.

• 대한의용생체공학회:의공학회지
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• 제15권4호
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• pp.489-497
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• 1994

The most serious problems related to the cardiovascular prothesis are thrombosis and hemolysis. It is known that the flow pattern of cardiovascular prostheses is highly correlated with thrombosis and hemolysis. Laser Doppler Anemometry (LDA) is a usual method to get flow pattern, which is difficult to operate and has narrow measure region. Particle Image Velocimetry (PIV) can solve these problems. Because the flow speed of valve is too high to catch particles by CCD camera, high-speed camera (Hyspeed : Holland-Photonics) was used. The estimated maximum flow speed was 5m/sec and maximum trackable length is 0.5 cm, so the shutter speed was determined as 1000 frames per sec. Several image processing techniques (blurring, segmentation, morphology, etc) were used for the preprocessing. Particle tracking algorithm and 2-D interpolation technique which were necessary in making gridrized velocity pronto, were applied to this PIV program. By using Single-Pulse Multi-Frame particle tracking algorithm, some problems of PIV can be solved. To eliminate particles which penetrate the sheeted plane and to determine the direction of particle paths are these solving methods. 1-D relaxation fomula is modified to interpolate 2-D field. Parachute artificial heart valve which was developed by Seoul National University and Bjork-Shiely valve was testified. For each valve, different flow pattern, velocity profile, wall shear stress and mean velocity were obtained.

• 한국도로학회논문집
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• 제20권1호
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• pp.9-18
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• 2018

PURPOSES : In this research, the initiation and development of corrugation on a gravel road with certain wheel and boundary conditions were evaluated using a coupled discrete-element method (DEM) with multibody dynamics (MBD). METHODS : In this study, 665,534 particles with a 4-mm diameter were generated and compacted to build a circular roadbed track, with a depth and width of 42 mm and 50 mm, respectively. A single wheel with a 100-mm diameter, 40-mm width, and 0.157-kg mass was considered for the track. The single wheel was set to run slowly on the track with a speed of 2.5 rad/s so that the corrugation was gradually initiated and developed without losing contact between the wheel and the roadbed. Then, the shape of the track surface was monitored, and the movement of the particles in the roadbed was tracked at certain wheel-pass numbers to evaluate the overall corrugation initiation and development mechanism. RESULTS : Two types of corrugation, long wave-length and short wave-length, were observed in the circular track. It seems that the long wave-length corrugation was developed by the longitudinal movement of surface particles in the entire track, while the short wave-length corrugation was developed by shear deformation in a local section. Properties such as particle coefficients, track bulk density, and wheel mass, have significant effects on the initiation and development of long-wave corrugation. CONCLUSIONS : It was concluded that the coupled numerical method applied in this research could be effectively used to simulate the corrugation of a gravel road and to understand the mechanism that initiates and develops corrugation. To derive a comprehensive conclusion for the corrugation development under various conditions, the driver's acceleration and deceleration with various particle gradations and wheel-configuration models should be considered in the simulation.

• 열처리공학회지
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• 제22권3호
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• pp.155-161
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• 2009

An investigation of the deformation behavior of ${\gamma}'-Ni_3Al$ single crystals containing fine dispersion of disordered ${\gamma}$ particles was performed for several different crystal orientations. Deformation structures were observed by the weak-beam method of transmission electron microscopy (TEM). The critical resolved shear stress (CRSS) for (111) [$\bar{1}$01] slie. increases with increasing temperature in the temperature range where (111) slip operates. The CRSS for (111) [$\bar{1}$01] slip is dependent on crystal orientation in the corresponding temperature range. The temperature where the strenjlth reaches a maximum is dependent on crystal orientation; the higher the ratio of the Schmid factors of (010) [$\bar{1}$01] to that of (111) [$\bar{1}$01], the higher the peak temperature. The peak temperatures were increased by the precipitation of y particles for the samples of all orientations. Electron microscopy of deformation induced dislocation arrangements under peak temperature has revealed that most of dislocations are straight screw dislocations. The mobility of screw dislocations decreases with increasing temperature. Above the peak temperature, dislocations begin to cross slip from the (111) [$\bar{1}$01] slip system to the (010) [$\bar{1}$01] slip system, thus decreasing the strength.

• 천문학회지
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• 제29권2호
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• pp.119-136
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• 1996

To examine the effect of neighboring galaxies on the gravitational lensing statistics, we performed numerical simulations of lensing by many galaxies. The models consist of a galaxy in the rich cluster like Coma, or a galaxy surrounded by field galaxies in $\Omega_0 = 1$ universe with $\Omega_{gal} = 0.1,\;\Omega_{gal} = 0.3\;or\;\Omega_{gal}=1.0\;,\;where\;\Omega_{gal}$ is the total mass in galaxies. Field galaxies either have the same mass or follow Schechter luminosity function and luminosity-velocity relation. Each lensing galaxy is assumed to be singular isothermal sphere (SIS) with finite cutoff radius. In most simulations, the lensing is mainly due to the single galaxy. But in $\Omega_{gal} = 3$ universe, one out of five simulations have 'collective lensing' event in which more than two galaxies collectively produce multiple images. These cases cannot be incorporated into the simple 'standard' lensing statistics calculations. In cases where 'collective lensing' does not occur, distribution of image separation changes from delta function to bimodal distribution due to shear induced by the surrounding galaxies. The amount of spread in the distribution is from a few $\%\;up\;to\;50\%$ of the mean image separation in case when the galaxy is in the Coma-like cluster or when the galaxy is in the field with $\Omega_{gal} = 0.1\;or\;\Omega_{gal}=0.3.$ The mean of the image separation changes less than $5\%$ compared with a single lens case. Cross section for multiple image lensing turns out to be relatively insensitive to the presence of the neighboring galaxies, changing less than $5\%$ for Coma-like cluster and $\Omega_{gal}=0.1,\;0.3$ universe cases. So we conclude that Coma-like cluster or field galaxies whose total mass density $\Omega_{gal}<0.3$ do not significantly affect the probability of multiple image lensing if we exclude the 'collective lensing' cases. However, the distribution of the image separations can be significantly affected especially if the 'collective lensing' cases are included. Therefore, the effects of surrounding galaxies may not be negligible when statistics of lensing is used to deduce the cosmological informations.

• 한국철도학회논문집
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• 제13권6호
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• pp.546-551
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• 2010

본 연구에서는 단일겹치기 접착 체결부에 대한 유한요소해석을 통해 요소의 조밀도 및 유한요소의 종류에 따른 접착 층의 변형률 분포를 Tsai의 시험치 와 비교하여 분석하였다. 이를 위해 접합부재의 길이방향, 접착체결부의 길이방향, 접합부재의 두께방향, 접착 층의 두께방향 및 조인트의 폭방향의 요소 조밀 도를 변화시켰다. 또한, 솔리드, 쉘 및 평면 변형률 요소에 따른 효과도 분석하였다. 해석은 단일 겹치기 접착 체결부의 대변형을 고려하기 위한 기하학적 비선형 해석을 수행하였다. 이를 통해 솔리드 요소를 적용할 경우 접착부재의 길이방향으로의 요소 수는 최소 2개 이상이면 해석의 신뢰도를 확보할 수 있음을 확인할 수 있었다. 쉘 요소의 겨우 x/c=1에서 수직 변형률의 시험결과와 22.8%의 오차를 보였으나, 전단응력의 경우에는 1.67%로 시험치와 거의 일치하였다.

• Advanced Composite Materials
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• 제17권3호
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• pp.277-299
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• 2008

High quality and expedient processing repair methods are necessary to enhance the service life of bridge structures. Deterioration of concrete can occur as a result of structural cracks, corrosion of reinforcement, and freeze.thaw cycles. Cost effective methods with potential for field implementation are necessary to address the issue of the vulnerability of bridge structures and how to repair them. Most infrastructure related applications of fiber-reinforced plastics (FRPs) use traditional hand lay-up technology. The hand lay-up is tedious, labor-intensive and relies upon personnel skill level. An alternative to traditional hand lay-up of FRP for infrastructure applications is Vacuum Assisted Resin Transfer Molding (VARTM). VARTM uses single sided molding technology to infuse resin over fabrics wrapping large structures, such as bridge girders and columns. There is no work currently available in understanding the interface developed, when VARTM processing is adopted to wrap fibers such as carbon and/or glass over concrete structures. This paper investigates the interface formed by carbon fiber processed on to a concrete surface using the VARTM technique. Various surface treatments, including sandblasting, were performed to study the pull-off tensile test to find a potential prepared surface. A single-lap shear test was used to study the bond strength of CFRP fabric/epoxy composite adhered to concrete. Carbon fiber wraps incorporating Sikadur HEX 103C and low viscosity epoxy resin Sikadur 300 were considered in VARTM processing of concrete specimens.

• Nuclear Engineering and Technology
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• 제53권4호
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• pp.1119-1126
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• 2021

Spacer grid with mixing vane had been widely used in nuclear reactor core. One of the main feather of spacer grid with mixing vane was that strong swirl flow was formed after the spacer grid. The swirl flow not only changed the bubble generation in the near wall field, but also affected the bubble behaviors in the center region of the subchannel. The interaction between bubble and the swirl flow was one of the basic phenomena for the two phase flow modeling in fuel assembly. To obatin better understanding on the bubble behaviors in swirl flow, full three dimension numerical simulations were conducted in the present paper. The swirl flow was assumed in the cylindral calculation domain. The bubble interface was captured by Volume Of Fluid (VOF) method. The properties of saturated water and steam at different pressure were applied in the simulation. The bubble trajectory, motion, shape and force were obtained based on the bubble parameters captured by VOF. The simulation cases in the present study included single bubble with different size, at different angular velocity conditions and at different pressure conditions. The results indicated that bubble migrated to the center in swirl flow with spiral motion type. The lateral migration was mainly related to shear stress magnitude and bubble size. The bubble moved toward the center with high velocity when the swirl magnitude was high. The largest bubble had the highest lateral migration velocity in the present study range. The effect of pressure was small when bubble size was the same. The prelimenery simulation result would be beneficial for better understanding complex two phase flow phenomena in fuel assembly with spacer grid.