• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.1935-1946
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• 2013

In this study, the behavior characteristics of bent pile structures with varying cross-section was examined through the measured results of field load test. A framework for determining the bending stress is calculated based on the stresses in the circumference of the pile using 3D finite element analysis. It is found that the bending stress near the pile-column joint changes rapidly and fracture zones occurs easily at variable cross-sections in bent pile structures. Also, the optimized column-pile diameter ratio was analyzed through the relationship between the column-pile diameter ratio and lateral crack load ratio. Based on this study, the optimized column-pile diameter ratio can be obtained near the inflection point of the curve between the column-pile diameter ratio and lateral crack load ratio. Therefore, a present study by considering the optimized variable cross-section condition would be improved bent pile structures design.

• Journal of the Korean Wood Science and Technology
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• v.31 no.2
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• pp.69-76
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• 2003

Front columns of buildings were most severely damaged by insects. Hole diameter damaged by insects were different in each location on columns, that is, bottom, middle position, or top of columns. That mean various insects attacked on columns of wooden traditional buildings because kinds of each insect depends on the hole diameter. Specially, middle position of columns were harmed seriously. Hole diameters damaged by insects were various from 1 mm to 10 mm, but approximately 5 mm diameter was found most commonly.

• Journal of the Korean Geosynthetics Society
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• v.5 no.4
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• pp.19-25
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• 2006

To examine the general features of a sand-clay composite triaxial test by making specimen varying ratios of diameters (dw) of sand columns that are installed on the soft ground as drains to diameters (de) of drain zone so called drainage space ratio (n=de/dw), densities of the granular columns, and strength of soft soils round around. I also conducted a test to research the reinforcement ability and effects of the ground when the granular columns are wrapped with supplementary materials such as geotextile. The results of the triaxial compression test showed that the shear strength increase is much big when the granular columns are wrapped with supplementary materials, while the shear strength increases as the diameter and density of the granular column increase in general. Also the drainage space ratio shows a distinct increase just below 3 and a similar shear behavior to sand is appeared. The pore water pressure coefficient decreases as the drainage space ratio decreases, however, when the drainage space ratio is less than 3~4, it declines significantly as shown in the results of shear behavior.

• Journal of Korean Society of Steel Construction
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• v.21 no.5
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• pp.505-514
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• 2009

This paper describes the structural behavior and the ultimate strengths of circular hollow steel (CHS) sections based on a series of compression tests. The ultimate strengths of CHS section columns are mainly dependent on both diameter-thickness ratio and column slenderness ratio. For the CHS sections with a high diameter-thickness ratio, an elastic or an inelastic local buckling may occur prior to the overall buckling, and it may decrease the column strength. Test sections were fabricated from SM400 steel plate of 2.8 mm and 3.2 mm in thickness and were tested to failure. The diameter-thickness ratios of the test sections ranged from 45 to 170 to investigate the effect of local buckling on the column strength. The compression tests indicated that the CHS sections of lower diameter-thickness ratio than the yield limit in the current design specifications showed an inelastic local buckling and a significant post-buckling strength in the local mode. Their ultimate stresses were larger than the nominal yield stress. It was known that the allowable stresses of the sections predicted by the Korean Highway Bridge Design Specifications (2005) were too conservative in comparison with test results. The Direct Strength Method which was newly developed was calibrated for application to the CHS sections by the experimental and numerical results. The Direct Strength Method proposed can predict properly the ultimate strength of CHS section columns whether a local buckling and an overall buckling occur nearly simultaneously or not.

• Journal of Korean Society of Steel Construction
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• v.20 no.5
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• pp.655-663
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• 2008

In this research, the fire resistance of Concrete-Filled Circular Steel Tube Columns (CFT) was evaluated by numerical analysis. As the materials of CFT columns, the steel of SPSR 400 grade and the concrete of 27.5MPa, 37.8MPa strengths were used. Significant parameters,such as concrete strength, axial load, and cross-sectional dimensions were determined. To verify the accuracy of the numerical analysis,the analysis results were compared with the former experiment results. The effect of the fire resistance time, axial load ratio, cross-sectional dimensions and concrete strength was evaluated by comparison with the fire resistance of the square CFT columns. This research showed that the structural behavior and fire resistance from the findings of numerical parametric studies showed a similarity to that of the experimental results. Therefore, this numerical analysis is reasonable in estimating the fire resistance of the circular CFT column.

• Journal of Korean Society of Steel Construction
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• v.19 no.6
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• pp.703-714
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• 2007

The aim of this research is to evaluate the fire resistance of concrete-filled steel square tube columns (square CFT columns) under constant axial loads by numerical analysis. The authors examined the experimental results on the fire resistance of concrete-filled steel square tube columns without fire protection. As the materials of CFT columns, steel of SPSR 400 grade and concrete of 27.5MPa and 37.8MPa strengths were used. The significant parameters were determined, such as load ratio, cross-sectional dimensions, and concrete strength. Detailed analytical simulations of fire resistance and axial deformation showed good agreement with the experimental observations. Therefore, this numerical analysis exhibited a reasonable estimation of fire resistance of the square CFT column. Results of the numerical parametric studies showed that the fire resistance of the CFT columns increased with the decrease of the concrete strength and the increase of the cross-sectional dimensions about the constant axial load ratio ($N/N_c$).

• Journal of the Korean Wood Science and Technology
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• v.37 no.3
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• pp.177-183
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• 2009

Characteristics analysis and species identification of post were carried out in four old traditional wooden frame houses in Cheongdo-gun. The diameter and height of post, and distance between posts are related with each other. It was considered that the traditional wooden frame houses were constructed according to the diameter and height of post as a basic dimension in distance between posts. Of the wood member samples obtained in the site, softwoods in three old houses and hardwoods in one old house were separated through light microscopy. The hardwoods were found to be Castanea crenata. and softwoods were all identified as Pinus densiflora.

• Composites Research
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• v.25 no.1
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• pp.19-25
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• 2012

The study investigated the buckling behavior of sandwich composite columns with different hole sizes and hole positions when they were applied to a compressive load. The columns consisted of 1.7mm thick faces of glass fabric/epoxy and 23mm, 37mm, 48mm, and 61mm thick cores of urethane-foam. Different hole sizes with the diameter of 25mm and 38mm were considered in this experiment. To evaluate the effect of hole position on the buckling behavior, we considered three types of hole position: 25mm diameter hole located at the center, 25mm diameter hole at 1/4 position from the center to the end of the column, and 25mm diameter hole at 1/2 position from the center to the end of the column. According to the results, buckling and maximum loads of the column having 25mm diameter hole were lower by 10% compared to those of the column without hole, whereas the loads for the column having 38mm diameter hole were 30% less than those of the column without hole. Hole position appeared to have no effect on buckling and maximum loads. Major failure modes were observed as follows: the core shear failure for the thin columns having 23mm and 37mm thick cores, and the face-core debonding for the thick columns having 48mm and 61mm thick cores.

• Journal of Korean Society of Steel Construction
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• v.27 no.4
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• pp.399-410
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• 2015

Concrete filled steel tube(CFT) has outstanding deformation capacity and strength in comparison with reinforced concrete or steel tube. CFT drilled shaft, which is developed large shear force due to seismic load and soil liquefaction, is designed as large diameter. However, shear design equations of the current standards do not consider bond stress of CFT and it results in extremely conservative design. Currently, previous studies for improving shear equations scarcely exist and are impossible applied to large CFT drilled shafts since these studies focus on only small scale experimental research. In this study, eventually to propose improving shear equation of large diameter CFT, it is preliminary research to compare and investigate the previous studies and current standards.

• Journal of the Korean Geotechnical Society
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• v.30 no.11
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• pp.25-37
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• 2014

Clay or sand does not exist alone but various sizes of soil are mixed in the field. In this study, the effect of water content on large deformation of such mixed soils is studied by using soil column tests and a particle method. A soil column with 7 cm in diameter and 13 cm in height, which was made out of kaolinite with sand content of 0, 10, 25, or 50%, was tested for large deformation. Its deformation was monitored with time. While increasing its water content from 40, 60, to 80%, a total of 12 types of soil column tests were carried out. The particle method simulated their deformation with time. A maximum plastic shear modulus, which was a function of undrained shear strength and plasticity index for soils with different water contents, was associated with soil viscosity to simulate large deformation of soil column. When a sand content of soil column was constant, the deformation of soil column increased with increasing water content. When a water content of soil column was constant, large deformation occurred with increasing the sand content. The maximum deformation, which was 22 cm in diameter, was observed in the case of water content of 80% and sand content of 50%. The particle method was able to relatively well simulate such large deformation and stress change of soils.