• 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.

• Journal of the Korea Concrete Institute
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• v.22 no.4
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• pp.481-488
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• 2010

Since existing constitutive models developed for confined normal strength concrete overestimate ductility when they are applied to confined high strength concrete, these models cannot be directly applied to confined high strength concrete. In an effort to solve this problem, an accurate stress-strain relationship of the hihg strength concrete needs to be formulated by examining the confinement effects due to increase of the concrete strength. In this study, a constitutive model is developed to express the stress-strain relationship of confined high strength concrete by carrying out regression analysis of the main parameters affection strength and ductile behavior of reinforced high strength concrete columns. Twenty-five test specimens were chosen from the reported experimental studies in the literature. The experimental results of stress-strain relationships of show a good agreement with results of the stress-strain relationships of suggested high strength concrete, covering a strength range between 60 and 124 MPa.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.1
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• pp.54-62
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• 2019

In this paper, a stress-strain model for high-strength confined concrete is proposed using compressive fracture energy. In the compression test performed by author in Reference [6], an acrylic bar with strain gauges was embedded in the center of the specimen to measure the local strain distribution. It was found from the test that the local strain measurement by this acrylic rod is very effective. The local fracture zone length was defined based on the local strain distribution measured by the acrylic rod. Specifically, it was defined as the length where the local strain increases more than twice of the strain corresponding to maximum stress. In addition, the stress-strain relationship of confined concrete with compressive fracture energy is proposed on the assumption that the amount of energy absorbed by the compressive members subjected to the given lateral confining pressure is constant regardless of the aspect ratio and size. The proposed model predicts even results from other researchers accurately.

• Journal of Korean Society of Steel Construction
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• v.22 no.4
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• pp.365-375
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• 2010

Concrete-filled steel tube columns are expected to have confined effects of the steel on the concrete and reinforced local buckling effects of the concrete. After comparing the results of existing studies with the experimental results from this study, the stress-strain relations were modified by evaluating the load-displacement with consideration of the confined effects. The effects of the parameters on the load-displacement and moment-curvature relationship according to the sectional and material properties were analyzed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.743-752
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• 2006

Confined concrete has enhanced strength and ductility compared with unconfined strength. Cause of these merits of confined concrete, many researches have been performed for confining effects of concrete and been studied in many fields. Although many researches about concrete confined by FRP sheets have been studied recently, it is difficult to apply concrete confined by FRP in real structures because FRP is a brittle material. In this study, the enhanced strength and ductility of concrete which is confined by steel tubes or steel plates were investigated. Fifty one specimens were tested and each specimen has different confining condition. Test results showed enhanced ductility and strength of confined concrete and concrete models were suggested under various confining conditions by regression of experimental data.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.578-588
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• 2002

An experimental study was conducted to investigate the effectiveness of transverse reinforcement in reinforced concrete tied columns subjected to monotonically increasing axial compression. Eighteen large-scale columns(260$\times$260$\times$1200 mm) were tested. Effects of main variables such as the concrete compressive strength, the tie configuration, the transverse reinforcement ratio, the tie spacing, and the spatting of the concrete cover were considered. High-strength concrete columns under concentric axial loads show extremely brittle behavior unless the columns are confined with transverse reinforcement that can provide sufficiently high lateral confinement pressure There is a consistent decrease in deformability of column specimen with increasing concrete strength. Test results were compared with the previous confinement model such as modified Kent-Park, Sheikh-Uzumeri, Mander, and Saatcioglu-Razvi model. The comparison indicates that many previous models for confined concrete overestimate or underestimate the ductility of confined concrete.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.3
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• pp.39-48
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• 2010

Improved seismic performances of RC bridges can be attained by sufficient ductilities of piers, which can be obtained by providing sufficient lateral confinements to the plastic hinge regions of piers. The cross sectional shape and the amount of lateral reinforcements are key parameters in the determination of effective confinements. Even though identical amounts of lateral reinforcement are provided, the effective confinement differs due to different spacing, arrangements, hook details and so on. Unlike circular sections in which confinement is exerted by mere hoop reinforcements, cross-ties are arranged in square or rectangular sections to enhance the effective confinements. The stress-strain relationship of confined concrete is varied by how to consider these cross-ties. In this study, the stress-strain relationships of confined concrete with cross-ties are investigated experimentally and their mechanical characteristics are estimated by comparison with other empirical equations.

• Journal of the Korea Concrete Institute
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• v.16 no.4 s.82
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• pp.501-509
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• 2004

The proposed model can predict the compressive behaviors of concrete confined with fiber reinforced polymer (FRP) jacket. To model confining concrete by FRP jackets, the hypoelasticity-based constitutive law of concrete In tri-axial stress states has been presented. The increment of strength of concrete has been determined by the failure surface of concrete in tri-axial states, and its corresponding peak strain is computed by the strain enhancement factor that is proposed in the present study, Therefore, the newly proposed model is a load-dependent confinement model of concrete wrapped by FRP jackets to compare the previous models which are load-independent confinement models. The behavior of FRP jackets has been modeled using the mechanics of orthotropic laminated composite materials in two-dimension. The developed model is implemented into the incremental analysis of compressive tests. The verification study with several different experiments shows that the model is able to adequately capture the behavior of the compression test by including better estimations of the axial responses as well as the lateral response of FRP-confined concrete cylinders.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.2
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• pp.207-216
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• 2005

External confinement by CFS (Carbon Fiber Sheet) is a very effective retrofit method for the reinforced concrete columns subject to either static or seismic loads. For the reliable and cost-effective design of CFS, an accurate stress-strain model is required for CFS-confined concrete. In this paper, uniaxial compression test on short RC column with square section was performed. To evaluate the effect of confinement on the stress-strain relationship of CFS-confined concrete, CFS area ratio and tie area ratio are considered. Based on the experimental results, a stress-strain model is proposed for concrete confined by CFS wraps. In the development of the model, the method to compute the actual hoop strains in CFS jackets at the rupture was examined and resolved. Overall, the results of the model agree well with test data.

• Journal of the Korean Society of Hazard Mitigation
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• v.3 no.2 s.9
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• pp.127-137
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• 2003

In locations where the cost of concrete is relatively high, or in situations where the weight of concrete members is to be kept to a minimum, it may be economical to use hollow R.C. members. The ductility of circular hollow R.C. columns with one layer of longitudinal and spiral reinforcement placed near the outside face of the section and the steel tube placed on the inside face of the section is investigated. Such hollow sections are confined through the wall thickness since the steel tube is placed. In this study, moment-curvature analyses are conducted with Mander's confined concrete stress-strain relationship. The variables influenced on the ultimate strain is the ratio and yield strength of confining reinforcement and the compression strength for confined concrete. From this ultimate strain - the transverse reinforcement ratio relationship, the transverse reinforcement ratio for circular hollow reinforced columns with confinement is proposed. The proposed transverse reinforcement ratio is confirmed by experimental results.