• Journal of Mechanical Science and Technology
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• v.20 no.11
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• pp.1980-1992
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• 2006

Nucleate pool boiling experiments were performed using pure R11 for various surface angles under constant heat flux conditions during saturated pool boiling. A 1-mm-diameter circular heater with an artificial cavity in the center that was fabricated using a MEMS technique and a high-speed controller were used to maintain the constant heat flux. Bubble growth images were taken at 5000 frames per second using a high-speed CCD camera. The bubble geometry was obtained from the captured bubble images. The effects of the surface angle on the bubble growth behavior were analyzed for the initial and thermal growth regions using dimensional scales. The parameters that affected the bubble growth behavior were the bubble radius, bubble growth rate, sliding velocity, bubble shape, and advancing and receding contact angles. These phenomena require further analysis for various surface angles and the obtained constant heat flux data provide a good foundation for such future work.

• Earthquakes and Structures
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• v.11 no.1
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• pp.141-163
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• 2016

Fiber models have been developed and applied to various structural elements such as shear walls, beams and columns. Only scarcely have fiber models been applied to circular foundation systems such as cast in drilled holes shafts (CIDH). In pile foundations with constraint head boundary conditions, shear deformations can easily contribute to the lateral pile response. However, soil structure interaction formulations such as the p-y method, commonly used for lateral pile design, do not include structural shear deformations in its traditional derivation method. A fiber model that couples shear and axial-bending behavior, originally developed for wall elements was modified and validated on circular cross sections (columns) before being applied to a 0.61 m diameter reinforced concrete (RC) pile with fixed head boundary conditions. The analytical response was compared to measured test results of a fixed head test pile to investigate the possible impact of pile shear deformations on the displacement, shear, and moment profiles of the pile. Results showed that shear displacements and forces are not negligible and suggest that nonlinear shear deformations for RC piles should be considered for fixed-head or similar conditions. Appropriate sensor layout is recommended to capture shear deformation when deriving p-y curves from field measurements.

• Publications of The Korean Astronomical Society
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• v.25 no.4
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• pp.119-128
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• 2010

Gaecheonjeol is the National Foundation day of Korea when people hold a harvest ceremony. Nowadays, two representative harvest ceremonies of Korea are performed at Mt. Mari (摩利山) and Mt. Taebaek (太白山) on Gaecheonjeol (October 3rd). We study 28 flags with constellations appearing in the ceremony of Mt. Taebaek. These flags are lying in the outer of the circular stone wall during the ceremony. They represent an oriental heavenly star chart. We examine the shape, the connecting-pattern, the name, and the number of constellations drawn in the flags, and find several errors, such as, a wrong position, a typo of name, an irregular size, an omission, and so forth. Traditionally, the 28 oriental constellations are usually divided into four groups and each group has its own colour for each direction: Blue (E), Black (N), White (W), and Red (S). For the constellation flags in Mt. Taebaek, the colour of the flags is painted based on geographical directions, but the constellations are arranged followed by the direction of the celestial sphere. Thus, constellations in the northern and southern parts are counterchanged. Finally, we suggest some possible criteria for constellation map of the flags in this paper. CheonSangYeolChaBunYaJiDo (天象列次分野之圖) and CheonMunRyuCho (天文類抄) can be essential references for correcting constellations drawn in the flags of Mt. Taebaek.

• Earthquakes and Structures
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• v.3 no.3_4
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• pp.203-230
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• 2012

This paper presents results for impedance (and compliance) functions and input motions of foundations in a layered half-space computed on the basis of a procedure that combines a consistent transmitting boundary with continued-fraction absorbing boundary conditions which are accurate and effective in modeling wave propagation in various unbounded domains. The effects of obliquely incident seismic waves in a layered half-space are taken into account in the formulation of the transmitting boundary. Using the numerical model, impedance (and compliance) functions and input motions of rigid circular foundations on the surface of or embedded in a homogeneous half-space are computed and compared with available published results for verification of the procedure. Extrapolation methods are proposed to improve the performance in the very-low-frequency range and for the static condition. It is concluded from the applications that accurate analysis of foundation dynamics and soil-structure interaction in a layered half-space can be carried out using the enhanced consistent transmitting boundary and the proposed extrapolations.

• Geomechanics and Engineering
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• v.35 no.1
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• pp.41-54
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• 2023

The use of a skirt, a vertical projection attached to the footing, is a recently developed method to increase the bearing capacity of soils and reduce foundation settlements. Most of the studies were focused on vertical skirted circular footings resting on clay while neglecting the rigidity and inclination of skirts. This study employs finite element limit analysis to investigate the bearing capacity enhancement of flexible and rigid inclined skirts in cohesionless soils. The results indicate that the bearing capacity initially improves with an increase in the skirt inclination but subsequently decreases for both flexible and rigid skirts. However, the rigid skirt exhibits more apparent optimum skirt inclination and bearing capacity enhancement than the flexible one, owing to differences in their failure mechanisms. Furthermore, the bearing capacity of the inclined skirted foundation increases with the skirt length, footing depth, and internal friction angle of the soil. In the case of rigid skirts, the bearing capacity increases linearly with skirt length, while for flexible skirts, it reaches a stable value at a certain skirt length. The efficiency of the flexible footing reduces as the footing depth and soil internal friction angle increase. Conversely, the efficiency of the rigid skirt decreases only with an increase in the depth of the footing. The paper also presents a detailed analysis of various failure patterns, highlighting the behaviour of inclined skirted footings. Additionally, nonlinear regression equations are provided to quantify and predict the bearing capacity enhancement with the inclined skirts.

• Geomechanics and Engineering
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• v.33 no.4
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• pp.381-391
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• 2023

The aim of this work is to analyze and predict the wave propagation behavior of the carbon nanotube reinforced composites (CNTRC) beams within the framework of various higher order shear deformation beam theory. Using the Euler-Lagrange principle, the wave equations for CNTRC beams are derived, where the determining factor is to make the determinant equal to zero. Based on the eigenvalue method, the relationship between wave number and circular frequency is obtained. Furthermore, the phase and group velocities during wave propagation are obtained as a function of wave number, and the material properties of CNTRC beams are estimated by the mixture rule. In this paper, various higher order shear beam theory including Euler beam theory, Timoshenko beam theory and other beam theories are mainly adopted to analyze the wave propagation problem of the CNTRC beams, and by this way, we conduct a comparative analysis to verify the correctness of this paper. The mathematical model provided in this paper is verified numerically by comparing it with some existing results. We further investigate the effects of different enhancement modes of CNTs, volume fraction of CNTs, spring factor and other aspects on the wave propagation behaviors of the CNTRC beams.

• Earthquakes and Structures
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• v.14 no.4
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• pp.323-336
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• 2018

Machine foundations with impact loads are common powerful sources of industrial vibrations. These foundations are generally transferring vertical dynamic loads to the soil and generate ground vibrations which may harmfully affect the surrounding structures or buildings. Dynamic effects range from severe trouble of working conditions for some sensitive instruments or devices to visible structural damage. This work includes an experimental study on the behavior of dry dense sand under the action of a single impulsive load. The objective of this research is to predict the dry sand response under impact loads. Emphasis will be made on attenuation of waves induced by impact loads through the soil. The research also includes studying the effect of footing embedment, and footing area on the soil behavior and its dynamic response. Different falling masses from different heights were conducted using the falling weight deflectometer (FWD) to provide the single pulse energy. The responses of different soils were evaluated at different locations (vertically below the impact plate and horizontally away from it). These responses include; displacements, velocities, and accelerations that are developed due to the impact acting at top and different depths within the soil using the falling weight deflectometer (FWD) and accelerometers (ARH-500A Waterproof, and Low capacity Acceleration Transducer) that are embedded in the soil in addition to soil pressure gauges. It was concluded that increasing the footing embedment depth results in increase in the amplitude of the force-time history by about 10-30% due to increase in the degree of confinement. This is accompanied by a decrease in the displacement response of the soil by about 40-50% due to increase in the overburden pressure when the embedment depth increased which leads to increasing the stiffness of sandy soil. There is also increase in the natural frequency of the soil-foundation system by about 20-45%. For surface foundation, the foundation is free to oscillate in vertical, horizontal and rocking modes. But, when embedding a footing, the surrounding soil restricts oscillation due to confinement which leads to increasing the natural frequency. Moreover, the soil density increases with depth because of compaction, which makes the soil behave as a solid medium. Increasing the footing embedment depth results in an increase in the damping ratio by about 50-150% due to the increase of soil density as D/B increases, hence the soil tends to behave as a solid medium which activates both viscous and strain damping.

• Journal of Korean Society of Steel Construction
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• v.28 no.2
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• pp.121-128
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• 2016

In order to suggest a reasonable design for the circular concrete filled tube steel column-foundation connection applying high-tension bolts, Overall structural behavior and characteristics according to various variables of column-foundation connection are numerically analyzed using a commercial FE analysis program, ABAQUS. To that goal, finite element analysis is conducted on the basis of the previous study replacing anchor bolts to high-tension bolts, and the analytical results are validated by comparison with experimental results. Also, the various variables(embedded depth and grade of anchor, and height and thickness of rib) involved in behavior of the column-foundation connection are selected through analyzing the current design criteria, and the characteristics of the column-foundation connection are compared and analyzed according to the various variables. In case of the anchor bolts, Applying the high-tension bolts is more advantage and securing the embedded depth beyond 0.5D is recommendable. In case of the rib, a minimum of 0.5D for rib's height and $0.4t_b$ for rib's thickness should be secured to develop the structural performance.

• Korean Journal of Heritage: History & Science
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• v.52 no.4
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• pp.264-271
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• 2019

Cheomseongdae in Gyeongju, known as an astronomical observatory, is a cultural monument with great historical, academic, and artistic value, as its unique shape is preserved well in its original form. The outer structure, ground stability, and seismic reliability of Cheomseongdae have been assessed by numerous researchers through various scientific methods, but research on the underground structure has been insufficient. This paper contains detailed models of the underground structure of Cheomseongdae interpreted in 2D and 3D images based on the data acquired through GPR surveys conducted of features in and around the base of Cheomseongdae. As a result, the existence of twelve small features arranged in a circle, although only about half of them remain, was confirmed at a depth of 0.4 - 0.6m. Furthermore, a structure three bays long (north-south direction) and four bays wide (east-west direction) was detected beneath Cheomseongdae at the depth of 0.7 - 1.0m. Other than 2 layers of foundations as is known, a square structure with the dimensions of 7m × 7m is situated at a depth of 0.6m, directly under Cheomseongdae, and what is reading that is expected to be the foundation structure of Cheomseongdae was detected and confirmed. This foundation structure is circular with a diameter in the east-west direction of 11m and in the north-south direction of 12m. The northern, western, and eastern edges of this foundation structure are about 1m away from the foundation of Cheomseongdae, whereas the the south side extends to about 5m wide.

• Journal of the Korean Geotechnical Society
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• v.36 no.10
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• pp.5-19
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• 2020

With increasing demand for offshore structures, the demand for temporary structures to help the offshore construction work has increased. A cofferdam is a temporary barrier to stop the inflow of water in the construction site and allows working in the dry condition when the construction is done within the water. However, it is a major cause of construction delays and increased costs because additional works are required to block the water inflow. Recently, in order to overcome the limitations of the conventional cofferdam methods and to increase economic efficiency, a large-diameter steel cofferdam method has been proposed which can be installed quickly in the seabed by using the suction pressure. In this circular steel cofferdam method, the top side of the cofferdam including the top-lid is always exposed above the sea level in order to use it as a water barrier, unlike the conventional suction bucket foundation. After installation, the top-lid of the cofferdam is removed and the water filled inside the cofferdam is discharged to make the interior dry condition. In this study, the circular steel cofferdam with a 5 m inner diameter was fabricated and the installation tests were conducted at the Saemaguem test site. During the experiment, variation of suction pressure, leakage between connections, structure deformation, and inclination of the steel cofferdam were measured and post-analyzed. This study verified the new circular steel cofferdam method and confirmed that the suction installation method can be successfully used for various purposes on offshore structures.