• Structural Engineering and Mechanics
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• v.18 no.2
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• pp.151-166
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• 2004

The interaction between concrete core expansion and deformation of perimeter ties has been known to have a significant effect on the effective confinement of rectangular reinforced concrete (RC) tied columns. This interaction produces passive confining pressure to the concrete core. Most existing models for determining the response of RC tied columns do not directly account for the influence of flexural stiffness of the ties and the variation of confining stress along the column height. This study presents a procedure for determining the confined compressive strength of RC square columns confined by rectilinear ties with various tie configurations considering directly the influence of flexural flexibility of the ties and the variation of confining stress along the vertical direction. The concept of area compatibility is employed to ensure compatibility of the concrete core and steel hoop in a global sense. The proposed procedure yields satisfactory predictions of confined strengths compared with experimental results, and the influence of tie flexibility, tie configuration and degree of confinement can be well captured.

• Advances in concrete construction
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• v.3 no.3
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• pp.161-185
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• 2015

FRP confining is a widely used method for seismic retrofitting of concrete columns. Several studies investigated the stress-strain behavior of FRP confined concrete prisms with square and rectangular sections both experimentally and analytically. In some studies, the monotonic stress-strain behavior of confined concrete was investigated and compressive strength models were developed. To study the reliability of these models, thorough statistical tests are required. This paper aims to investigate the reliability of the presented models using statistical tests including t-test, wilcoxon rank sum test, wilcoxon signed rank test and sign test with a level of significance of 5%. Wilk Shapiro test was also employed to evaluate the normality of the data distribution. The results were compared for different cross section and confinement types. To see the accuracy of the models when there were no significant differences between the results, the coefficient of confidence was used.

• Advances in concrete construction
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• v.1 no.3
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• pp.215-225
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• 2013

The results of experimental testing of the effect of confined concrete on compressive strength and ductility of concrete beam subjected to pure bending are presented. The effect of different stirrups forms and spacing, as well as different concrete strengths, on beam carrying capacity and ductility were analyzed. Ultimate strength capacity and deflection of concrete beam increase with the decrease in stirrups spacing. Stirrup form has a great effect on the ultimate carrying capacity and ductility of concrete beam. Stirrups which confined the region of concrete in the compression more contribute to greater compression strength of concrete than common stirrups at the perimeter of the entire cross-section of the beam.

• Structural Monitoring and Maintenance
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• v.6 no.3
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• pp.173-190
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• 2019

Steel-confined reinforced concrete (SCRC) columns feature highly complex and invisible mechanisms that make damage evaluation and pattern recognition difficult. In the present article, the prevailing acoustic emission (AE) technique was applied to monitor and evaluate the damage process of steel-confined RC columns in a quasi-static test. AE energy-based indicators, such as index of damage and relax ratio, were proposed to trace the damage progress and quantitatively evaluate the damage state. The fuzzy C-means algorithm successfully discriminated the AE data of different patterns, validity analysis guaranteed cluster accuracy, and principal component analysis simplified the datasets. A detailed statistical investigation on typical AE features was conducted to relate the clustered AE signals to micro mechanisms and the observed damage patterns, and differences between steel-confined and unconfined RC columns were compared and illustrated.

• International conference on construction engineering and project management
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• 2009.05a
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• pp.978-982
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• 2009

In recent years, due to some excellent properties of fiber reinforced polymer (FRP) composites, the use of FRP sheets for strengthening the weak concrete columns have become increasingly popular. Axial loading is the basic assumption in most of the models that are presented for estimating the compression strength of confined concrete columns. However a large number of weak concrete columns in the bending frames are under the combination of both axial and flexural loads. This paper presents the results of an experimental study on the effects of eccentricity of load on the compressive strength of concrete columns confined by FRP sheets. This research shows that the eccentricity of compression load affects decreasingly the performance of confining FRP jacket in confined columns.

• Advances in concrete construction
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• v.2 no.3
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• pp.177-192
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• 2014

One of the main applications of FRP composites is confining concrete columns. Hence identifying the cyclic and monotonic stress-strain behavior of confined concrete columns and the parameters influencing this behavior is inevitable. Two significant parameters affecting the stress-strain behavior are aspect ratio and corner radius. The present study aims to scrutinize the effects of corner radius and aspect ratio on different aspects of stress-strain behavior of FRP confined concrete specimens (rectangular, square and circular). Hence 44 FRP confined concrete specimens were tested and the results of the tests were investigated. The findings indicated that for specimens with different aspect ratios, the relationship between the ultimate stress and the corner radius is linear and the variations of the ultimate stress versus the corner radius decreases as a result of an increase in aspect ratio. It was also observed that increase of the corner radius results in increase of the compressive strength and ultimate axial strain and increase of the aspect ratio causes an increase of the ultimate axial strain but a decrease of the compressive strength. Investigation of the ultimate condition showed that the FRP hoop rupture strain is smaller in comparison with the one obtained from the tensile coupon test and also the ultimate axial strain and confined concrete strength are smaller when a prism is under monotonic loading. Other important results of this study were, an increase in the axial strain during the early stage of unloading paths and increase of the confining effect of FRP jacket with the increase and decrease of the corner radius and aspect ratio respectively, a decrease in the slope of reloading branches with cycle repetitions and the independence of this trend from the variations of the aspect ratio and corner radius and also quadric relationship between the number of each cycle and the plastic strain of the same cycle as well as the independence of this relationship from the aspect ratio and corner radius.

• Journal of Korean Society of Steel Construction
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• v.21 no.5
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• pp.461-470
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• 2009

A column resisting axial load and seismic load is one of the main members in a structural system. The heated column by event of a fire can lose its strength and it may damage its structural system or cause the collapse of the entire structural system. In this study, the fire resistance capacity of internally confined hollow concrete filled tube (ICH CFT) column was investigated. In an ICH CFT column, the yield strength of the external tube is important as a concrete filled tube (CFT) column because the external tube confines the filled concrete and the strength of the column depends on the confined effect. A study was performed by finite element analyses considering the confined effect and material nonlinearity as the temperature changes by the fire. The hollow ratio, the thickness of the external tube, and the strength of concrete were selected as the parameters for the analyses. The analyses were performed by using a commercial FEA program (ABAQUS) and nonlinear concrete model program. The analysis results showed that the hollow ratio and the strength of concrete mainly affect the fire resisting capacity of an ICH CFT column.

• Journal of the Korea Concrete Institute
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• v.19 no.3
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• pp.253-263
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• 2007

Previous researches showed that confined concrete with Fiber-Reinforced Plastic (FRP) sheets significantly improves the strength and ductility of concrete compared with unconfined concrete. However, the retrofit design of concrete with FRP materials requires an accurate estimate of the performance enhancement due to the confinement mechanism. The object of this research is to predict the compressive strength and strain of concrete confined with FRP wraps. For the purpose of this research, 102 test specimens were fabricated and loaded statically under uniaxial compression. Axial load, axial and lateral strains were investigated to predict the ultimate stress and strain. Also, to achieve reliability of proposed strength and strain models for FRP-confined concrete, another series of uniaxial compression test results were used. This paper presents strength and strain models for FRP-confined concrete. The proposed models to estimate the ultimate stresses and failure strains produce satisfactory predictions as compared to current design equations. In conclusion, it is proposed that the modified stress-strain model of concrete cylinders could be effectively used for the repair and retrofit of concrete columns.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.9
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• pp.1159-1164
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• 2018

Recently, Internet use is increasing in various fields. Especially in the sudden disaster area, the role of Internet of things that can continuously monitor is getting bigger. In this study, the characteristics of the confined space and the environmental hazards are examined, and the Internet of the object which is being commercialized will be reviewed. Accidents in confined spaces are very high compared to other places, and it is very difficult to predict accidents. Recently, various attempts have been made to prevent accidents in confined spaces using the Internet of things. Especially, it detects the various gases that can occur in the closed space using sensors and sends them to the workers in real time, so that the risk can be detected in advance to minimize the risk. In this paper, we propose an effective disaster prevention plan using the Internet of things through the case study of the Internet for the prevention of accidents in a confined space.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.29 no.4
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• pp.590-602
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• 2019

Objectives: This study was conducted to prevent asphyxiation of firefighters during confined space rescue. The specific purpose was to identify the magnitude of the problem, identify the cause of the accidents, and suggest measures to ensure safety of confined space rescues. Methods: We collected data from National Fallen Firefighters Memorial, press releases, and other sources In order to identify the current situation of asphyxiation incidents among firefighters from 1945 to 2019. In addition, an incident investigation was conducted for each case, and the processes, causes, and control measures of the incidents were described as a narrative data entry. Results: Over the past 73 years, eight incidents involving firefighter in Korea have occurred. In these incidents, five firefighters were killed, and eight were injured. The confined spaces incidents occurred were water supply tanks, wastewater treatment tanks, pickling pits, septic tanks, and more. The causes were three cases of hydrogen sulfide poisoning, one of oxygen deficiency, one of carbon monoxide poisoning, and three unclassifiable asphyxiations. The people in need were all workers in various industries. Conclusions: The number of firefighters' deaths and injuries during rescues in confined spaces was severe and the risks have not been completely eliminated. By establishing and implementing a precise incident investigation system, according control measures should be initiatedin order to prevent a recurrence of the same type of disaster and reflected in the SOP. In particular, due to the high risk of occurrence at workplaces, cooperation between fire and rescue authority and relevant agencies such as the Ministry of Employment and Labor and the KOSHA should be strengthened.