• Journal of the Korean Institute of Rural Architecture
• /
• v.6 no.3
• /
• pp.106-115
• /
• 2004

In this paper, the compressive strength and ductility enhancement of concrete by lateral confinement of carbon-fiber sheets(CFS) have been studied experimentaly with cylinder specimens and square short columns reinforced externally by CFS. Test variables were amount of lateral reinforcement by CFS and space of hoop bars. Test results showed that lateral reinforcements by carbon-fiber sheets provided lateral confinement successfully for the concrete specimens and were more effective for ductility enhancement than for strength increase, and that the lateral confinement coefficient of cabon-fiber sheets increased according to narrowing the space of hoop bars in the double lateral confinement made by CFS and hoop bars.

• Structural Engineering and Mechanics
• /
• v.3 no.6
• /
• pp.593-609
• /
• 1995

The presence of reinforcement has a significant influence on the stress-strain behaviour of reinforced concrete structures, expecially when the failure stage of the structures is approached. In the present paper, the constrained and non-constrained zones of concrete due to the presence of reinforcement is developed and the stress-stress-strain behaviour of concrete is enhanced by a reinforcement confinement coefficient, Furthermore, a flexible method for the modelling of reinforcement with arbitrary orientation and not passing the nodes of concrete element is also proposed. Numerical examples and laboratory tests have shown that the coefficient and the modelling technique proposed by the author are satisfactory.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2002.05a
• /
• pp.835-840
• /
• 2002

The purpose of this study is to analyze the reinforcement effect of the RC compressive member confined with carbon fiber sheets and to suggest better transverse confinement coefficient(k$_1$) than one's in the existing analysis equations. Showing amounts of CPS in terms of ratio of transverse reinforcement to cross-section, it comes to be possible to calculate the objective and quantitative reinforcement amounts and to estimate the overlapping length of CFS that can influence on all its confinement effect. The previous parameters were compared using the existing experimental test data, then analyzed for the merits and demerits of existing parameters through the coefficient of correlation(R). The proposed parameters were derived in such a way that established parameters and their combination were obtained from the analytical study and then determined by regression analysis using the previous test data.

• Steel and Composite Structures
• /
• v.16 no.1
• /
• pp.59-75
• /
• 2014

A new concrete confinement model is developed to predict the axial load versus displacement behavior of circular columns under concentric axial load. The new confinement model is proposed for concrete filled steel tube columns as well as circular reinforced concrete columns with steel tube jacketing. Existing confinement models were evaluated and improved using available experimental data from different sets of columns tested under similar loading conditions. The proposed model is based on commonly used confinement models with an emphasis on modifying the effective confining pressure coefficient utilizing the strength of the unconfined concrete and the steel tube, the length of the column, and the thickness of the steel tube. The proposed model predicts the ultimate axial strength and the corresponding strain with an acceptable degree of accuracy while also highlighting the importance of the manner in which the steel tube is used.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.305-308
• /
• 2008

The purpose of this study is to propose the confinement effectiveness of precast segmental concrete that binding by lateral confining steel in the method of precast segmental concrete pridge piers construction. Generally, the confinement effect of concrete that binding by lateral confining steel is defined by the confinement effectiveness coefficient and the confinement effectiveness coefficient is defined as the ratio of area of effectively confined concrete core to area of confined concrete core. The area of effectively confined concrete core is defined by Arching action occurred on a space of lateral confinement steel and The area of confined concrete core is defined by the ratio of area of longitudinal reinforcement to area of core of section. But in case of precast segmental concrete, concrete cover that exist on top and bottom of concrete segment should be considered.

• Journal of Sensor Science and Technology
• /
• v.30 no.3
• /
• pp.139-147
• /
• 2021

Numerical analysis was performed using FIMMWAVE to optimize the specifications of Si₃N₄/SiO₂ slot and ridge-slot optical waveguides based on confinement factor and effective mode area. The optimized specifications were confirmed based on sensitivity in terms of the refractive index of the analyte. The specifications of the slot optical waveguide, i.e., the width of the slot and the width and height of the rails, were optimized to 0.2 ㎛, 0.46 ㎛, and 0.5 ㎛ respectively. When the wavelength was 1.55 ㎛ and the refractive index of the slot was 1.3, the confinement factor and effective mode area of 0.2024 and 2.04 ㎛², respectively, were obtained based on the optimized specifications. The thickness of the ridge and the refractive index of the slot were set to 0.04 ㎛ and 1.1, respectively, to optimize the ridge-slot optical waveguide, and the confinement factor and effective mode area were calculated as 0.1393 and 2.90 ㎛², respectively. When the confinement coefficient and detection degree of the two structures were compared in the range of 1 to 1.3 of the analyte index, it was observed that the confinement coefficient and sensitivity were higher in the ridge-slot optical waveguide in the region with a refractive index less than 1.133, but the reverse situation occurred in the other region. Therefore, in the implementation of the integrated optical biochemical sensor, it is possible to propose a selection criterion for the two parameters depending on the value of the refractive index of the analyte.

• Steel and Composite Structures
• /
• v.30 no.4
• /
• pp.337-350
• /
• 2019

The objective of this paper is to investigate the confinement coefficient of concrete-filled square stainless steel tubular (CFSSST) stub columns under axial loading. A fine finite 3D solid element model was established, which utilized a constitutive model of stainless steel considering the strain-hardening characteristics and a triaxial plastic-damage constitutive model of concrete with features of the parameter certainty under axial compression. The finite element analysis results revealed that the increased ultimate bearing capacity of CFSSST stub columns compared with their carbon steel counterparts was mainly due to that the composite action of CFSSST stub columns is stronger than that of carbon steel counterparts. A further parametric study was carried out based on the verified model, and it was found that the stress contribution of the stainless steel tube is higher than the carbon steel tube. The stress nephogram was simplified reasonably in accordance with the limit state of core concrete and a theoretical formula was proposed to estimate the ultimate bearing capacity of square CFSSST stub columns using superposition method. The predicted results showed satisfactory agreement with both the experimental and FE results. Finally, the comparisons of the experimental and predicted results using the proposed formula and the existing codes were illustrated.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2003.11a
• /
• pp.351-354
• /
• 2003

Triaxial behavior of concrete cylinders wrapped with FRP material has been investigated for the increase of concrete strength by lateral confinement. Using the model by Richart et al., a modified empirical equation was proposed to estimate the strength of concrete cylinders with FRP confinement based on the linear relationship between the concrete strength and lateral confining pressure. From the experimental stress-strain result of the cylinder specimens having similar confining pressure, less ductility was observed for higher strength concrete. But the compressive strength of the specimen was linearly increased by lateral confinement. The confinement effectiveness coefficient for the strength enhancement of the cylinders by FRP wrap was obtained as 2.27 from the regression analysis.

• Steel and Composite Structures
• /
• v.29 no.4
• /
• pp.465-481
• /
• 2018

The use of external carbon-fiber-reinforced polymer (CFRP) laminates is one of the most effective techniques existing for the confinement of circular concrete specimens. Currently, several researches have been made to develop models for predicting the ultimate conditions of this type of confinement. As most of the major existing models were developed based on limited experimental database. This paper presents the development of new confinement ultimate conditions, strength and strain models, for concrete cylinders confined with CFRP composites based on a statistical analysis of a large existing experimental database of 310 cylindrical concrete specimens wrapped with CFRP. The database is used to evaluate the performance of the proposed and major existing strength and strain models. Based on the two different statistical indices, the coefficient of determination ($R^2$) and the Root Mean Square Error (RMSE), the two proposed confinement ultimate conditions presents a good performance compared to the major existing models except the models of Lam and Teng (2003) and Youssef et al. (2007) which have relatively similar performance to the proposed models.

• Steel and Composite Structures
• /
• v.31 no.1
• /
• pp.13-25
• /
• 2019

Reactive powder concrete (RPC) is a type of ultra-high strength concrete that has a relatively high brittleness. However, its ductility can be improved by confinement, and the use of RPC in composite RPC filled steel tube columns has become an important subject of research in recent years. This paper aims to present an experimental study of axial capacity calculation of RPC filled circular steel tube columns. Twenty short columns under axial compression were tested and information on their failure patterns, deformation performance, confinement mechanism and load capacity were presented. The effects of load conditions, diameter-thickness ratio and compressive strength of RPC on the axial behavior were further discussed. The experimental results show that: (1) specimens display drum-shaped failure or shear failure respectively with different confinement coefficients, and the load capacity of most specimens increases after the peak load; (2) the steel tube only provides lateral confinement in the elastic-plastic stage for fully loaded specimens, while the confinement effect from steel tube initials at the set of loading for partially loaded specimens; (3) confinement increases the load capacity of specimens by 3% to 38%, and this increase is more pronounced as the confinement coefficient becomes larger; (4) the residual capacity-to-ultimate capacity ratio is larger than 0.75 for test specimens, thus identifying the composite columns have good ductility. The working mechanism and force model of the composite columns were analyzed, and based on the twin-shear unified strength theory, calculation methods of axial capacity for columns with two load conditions were established.