• Journal of the Korea institute for structural maintenance and inspection
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• v.5 no.3
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• pp.163-171
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• 2001

Lateral confinement pressure generate improvements in strength and ductility of confined concrete. Carbon fiber sheets have a lot of merits, such as light weight, high strength and ease for construction, when it is applied to the defected structural member for the strengthening of shear and flexure. The purpose of this experimental study is to evaluate the strength characteristics of the reinforced concrete column confined with carbon fiber sheets. The main variables in this test are concrete strength ($290kgf/cm^2$ called N type, $505kgf/cm^2$ called H type) and pre-loading. In the test, a total of twelve specimens, which were all $10{\times}10cm$ in size, 117 cm in length, have a 2.85 reinforcement ratio, have been used. The results indicate that the strength was enhanced 26%~30% in N type, 11%~16% in H type specimens which was confined with carbon fiber sheets.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.31 no.4
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• pp.503-509
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• 2021

Objectives: The utility of the system was analyzed by applying the smart safety technology system to the aging pipe rehabilitation facility construction classified as a confined space. Methods: Smart safety management system was applied to a site where the aging pipe rehabilitation work was in progress. The working environment was measured for 25 days, and the toxic gas saturation was analyzed according to the working time and working place. Results: Based on the measured results, two characteristic environmental changes in the confined space were confirmed. First, when working inside an aging pipe, the tendency of carbon dioxide saturation increases with working time and the number of workers. Second, oxygen decreases when working in a space away from the entrance. Conclusions: Various applications of smart safety technology have been confirmed based on the measured data, and this is expected to be useful for environmental characteristic analysis and safety management when applied to a confined space composed with various conditions in the future.

• Journal of Powder Materials
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• v.27 no.6
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• pp.477-483
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• 2020

Metal-organic frameworks (MOFs) are of significant interest because of their high porosity, which facilitates their utilization in gas storage and catalysis. To enhance their current properties in these applications, it is necessary to elucidate the interactions between molecules in a confined environment that differ from those in bulk conditions. Herein, we study the confined molecular interaction by investigating the solvent-dependent photophysical properties of two different-sized molecules inside MOF-5. Ruthenium tris-bipyridine (Rubpy) and coumarin 153 (C153) are encapsulated in MOF-5. Rubpy with MOF-5 (Rubpy@MOF) is prepared by building MOF-5 around it, resulting in limited space for solvent molecules in the pores. The smaller C153 is encapsulated in the preformed MOF-5 (C153@MOF) by simply soaking the MOF in a concentrated C153 solution. C153@MOF permits more space for solvent molecules in the pore. Their characteristic absorption and emission spectra are examined to elucidate the confined molecular interactions. Rubpy@MOF and C153@MOF exhibit different spectral shifts compared to the guest molecules under bulk conditions. This discrepancy is attributed to the different micro-environments inside the pores, derived from confined host-guest interactions in the interplay of solvent molecules.

• Steel and Composite Structures
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• v.43 no.4
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• pp.431-445
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• 2022

A double-skinned composite tubular (DSCT) column, which is an internally confined concrete-filled tubular column with a hollow section, has been developed for efficient use of materials that reduce self-weight and enhance seismic performance. It exhibits excellent material behavior with ductility owing to the confinement induced by outer and inner steel tubes. This study conducted axial compression tests considering the effects of steel tube thickness and hollow diameter ratios of DSCT columns on the material behavior of confined concrete under pure axial compression on concrete cores. From the axial compression tests, various combinations of outer and inner tube thicknesses and two different hollow section ratios were considered. Additionally, confined concrete material behavior, axial strength, failure modes, and ductility of DSCT columns were evaluated. Based on this study, it was concluded that the tests show a good correlation with peak strength and shapes of nonlinear stress-strain curves presented in literature; however, the thinner outer and inner steel tubes may reduce the ductility of DSCT columns when using thinner outer and inner tubes and higher confined stress levels. Finally, the minimum thickness requirements of the steel tubes for DSCT columns were discussed in terms of strength and ductility of test specimens.

• Steel and Composite Structures
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• v.43 no.2
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• pp.257-270
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• 2022

Recycled aggregate concrete (RAC) is rarely used in load-carrying structural members. To widen its structural application, the compressive behavior of a promising type of composite column, steel-fiber reinforced polymer (FRP) double-tube confined RAC column, has been experimentally and analytically investigated in this study. The objectives are the different performance of such columns from their counterparts using natural aggregate concrete (NAC) and the different mechanisms of the double-tube and single-tube confined concrete. The single-tube confined concrete refers to that in concrete-filled steel tubular (CFST) columns and concrete-filled FRP tubular (CFFT) columns. The test results showed that the use of recycled coarse aggregates (RCA) affected the axial load-strain response in terms of deformation capacity but such effect could be eliminated with the increasing confinement. The composite effect can be triggered by the double confinement of the steel and carbon FRP (CFRP) tubes but not by the steel and polyethylene terephthalate (PET) FRP tubes. The proposed analysis-oriented stress-strain model is capable to capture the load-deformation history of such steel-FRP double-tube confined concrete columns under axial compression.

• Earthquakes and Structures
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• v.23 no.5
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• pp.431-444
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• 2022

The unique thermomechanical properties of shape memory alloys (SMAs) make it a versatile material for strengthening and repairing structures. In particular, several research studies have already demonstrated the effectiveness of using the heat activated shape memory effect of nickel-titanium (Ni-Ti) based SMAs to actively confine concrete members. Despite the proven effectiveness and wide commercial availability of Ni-Ti SMAs, however, their high cost remains a major obstacle for applications in real structural engineering projects. In this study, the shape memory effect of a new, much more economical iron-based SMA (Fe-SMA) is characterized and the compressive behavior of concrete confined with Fe-SMA strips is investigated. Tests showed the Fe-SMA strips used in this study are capable of developing high levels of recovery stress and can be easily formed into hoops to provide effective active and passive confining pressure to concrete members. Compared to concrete cylinders confined with conventional carbon fiber-reinforced polymer (CFRP) composites, Fe-SMA confinement yielded significantly higher compressive deformation capacity and residual strength. Overall, the compressive behavior of Fe-SMA confined concrete was comparable to that of Ni-Ti SMA confined concrete. This study clearly shows the potential for Fe-SMA as a robust and cost-effective strengthening solution for concrete structures and opens possibilities for more practical applications.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3A
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• pp.265-275
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• 2010

Concrete filled steel tube and concrete encased steel tube columns are expected to have confined effects of concrete by steel and reinforced effects of local buckling by concrete. On the basis of confined state concrete models of previous researches, stress-strain and load-displacement relations of RC, CFT and CET columns are analyzed by steel ratio. After comparing analysis results with experimental results, Modified stress-strain relations are derived through evaluation the influence upon confined effects of concrete in each cases. Also, the modified stress-strain models are carried out to be compared with specified strength of various countries.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.462-471
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• 1997

In this study, we studied the compression test of laterally confined concrete cylinder by the carbon-fiber sheet(CFS), and compared the test results with previous test results and relationships by other researchers. Our objectives is to find the stress-strain characteristics and the enhancement of strength of the confined concrete to the lateral pressure offered by CFS.

• Korean Journal of Materials Research
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• v.14 no.3
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• pp.175-180
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• 2004

SiC nanotubes were synthesized by CNT-confined reaction. Evaporated SiO gas reacted with carbon nanotubes by VS growth mechanism. By confineded reaction, carbon nanotube was changed to SiC nanotube, and synthesized SiC nanotube was filled partly by the gas reaction in the nanotubes. SiC nanotube's mean diameters were not changed than carbon nanotubes because of means ratio of $CO_2$ and SiO gas was maintained evenly during the process. This result was same of data of simulation. By TEM observastion, SiC nanotube was filled by reaction of inner wall of CNT and SiO gas through the VS reactions. Converted SiC nanotube's compositions were revealed Si and C of 1: 1 ratios at all sites of nanotube by EDS.

• International Journal of Concrete Structures and Materials
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• v.18 no.2E
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• pp.133-142
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• 2006

An experimental study was conducted to investigate the effectiveness of transverse steel in reinforced concrete tied columns subjected to monotonically increasing axial compression. Eighteen large-scale columns($260{\times}260{\times}1,200mm$) were tested. Effects of such main variables as concrete compressive strength, configurations of transverse steel, transverse reinforcement ratio, spacing of transverse steel, and spalling of concrete cover were investigated. High-strength concrete columns under concentric axial loads show extremely brittle behavior unless the columns are confined with transverse steel that can provide sufficiently high lateral confinement pressure. A consistent decrease in the deformability of the column test specimens was observed with increasing concrete strength. Test results of this study were compared with existing confinement models of modified Kent-Park, Sheikh-Uzumeri, Mander, and Saatcioglu-Razvi. The comparison indicates many existing models to predict the behavior of confined concrete overestimate or underestimate the ductility of confined concrete.