• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.2 s.48
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• pp.73-81
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• 2006

The purpose of this study is to investigate the inelastic behavior of reinforced high-strength concrete bridge columns. A computer program, named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of reinforced concrete structures was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model ol reinforcing steel. The smeared rack approach is incorporated. The increase of concrete strength due to the lateral confining reinforcement has been also taken into account to model the confined high-strength concrete. The proposed numerical method for the inelastic behavior of reinforced high-strength concrete bridge columns is verified by comparison with reliable experimental results.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.549-552
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• 2009

본 논문에서는 재료적 성능이 우수하며 경량재료로서 최근 건설구조물에 활용하고자 하는 연구가 활발히 진행되고 있는 섬유보강재료(FRP : Fiber Reinforced Polymer)를 이용한 합성구조인 CFFT(Concrete Filled FRP Tube)의 설계프로그램을 개발하여 제안하고자 하였다. 먼저, CFFT구조는 FRP관에 의해 철근콘크리트가 구속되는 구조로서 기둥과 같이 축력이 도입되는 경우 포아송효과에 의한 변형을 FRP관이 구속효과를 줌으로써 콘크리트의 역학적 거동을 개선하게 되는데 본 연구에서는 실험에 의해 검증된 식을 제시하였으며 이를 바탕으로 CFFT구조를 설계하는 알고리즘을 제안하였다. 또한 CFFT구조는 FRP관의 구속으로 인해 고강도콘크리트와 긴장재의 도입이 가능한 구조로서 이에 대한 설계도 포함하였다. 그러나 이방성재료인 FRP의 설계와 동시에 FRP관에 의한 구속효과를 고려하는 CFFT구조의 설계는 일반 실무설계자들에게는 다소 난해한 작업으로써 전산화 설계프로그램의 필요성이 대두되어 본 연구에서 CFFT구조의 설계프로그램을 개발하였다. 개발된 설계프로그램의 검증을 위해 일반 철근콘크리트기둥, CFFT기둥, 고강도콘크리트와 PS긴장재를 도입한 CFFT기둥을 설계한 결과, 매우 실용적이며 타당한 설계가 수행될 수 있음을 확인하였다.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.201-204
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• 2008

The proposed method, capable of predicting various stress-strain responses in axially loaded concrete confined with FRP (Fiber Reinforced Polymers) composites in a rational manner, is based on the fact that the volumetric expansion due to progressive microcracking in mechanically loaded concrete is an important measure of the extent of damage in the material microstructure. The elastic modulus expressed as a function of area strain and concrete porosity, the energy-balance equation relating the dilating concrete to the confining device interactively, the varying confining pressure, and an incremental calculation algorithm are included in the solution procedure. This procedure enables the evaluation of lateral strains consecutively according to the related mechanical model and the energy-balance equation, rather than using an empirically derived equation for Poisson's ratio or dilation rate as in other analytical methods.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.4
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• pp.89-98
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• 2012

This study estimates the performance of steel spirals according to the compressive strength of the concrete. A total of 24 confined concrete cylinders ($150{\times}300mm$) were cast and tested under monotonic concentric compression. The main test parameters were the yield strength of spiral reinforcements and the compressive strength of the concrete. To effectively evaluate the confinement effect according to the yield strength of steel spirals, the external diameter of steel spirals was designed to be same as the diameter of specimen. The experimental results indicated that the performance of confinement of steel spirals increased as the yield strength of spiral reinforcement increased and the compressive strength of the concrete decreased. Furthermore, existing analytical models were used for predicting the stress versus axial strain relationships of specimens tested in this study. It can be concluded that the accuracy of the analytical models deteriorated as the yield strength of steel spirals and the compressive strength of the concrete increased.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.803-810
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• 2007

An analytical method capable of predicting various stress-strain responses in axially loaded concrete confined with FRP (fiber reinforced polymers) composites in a rational manner is presented. Its underlying idea is that the volumetric expansion due to progressive microcracking in mechanically loaded concrete is an important measure of the extent of damage in the material microstructure, and can be utilized to estimate the load-carrying capacity of concrete by considering the corresponding accumulated damage. Following from this, an elastic modulus expressed as a function of area strain and concrete porosity, the energy-balance equation relating the dilating concrete to the confining device interactively, the varying confining pressure, and an incremental calculation algorithm are included in the solution procedure. The proposed method enables the evaluation of lateral strains consecutively according to the related mechanical model and the energy-balance equation, rather than using an empirically derived equation for Poisson's ratio or dilation rate as in other analytical methods. Several existing analytical methods that can predict the overall response were also examined and discussed, particularly focusing on the way of considering the volumetric expansion. The results predicted by the proposed and Samaan's bilinear equation models correlated with observed results with a reasonable degree, however it can be judged that the latter is not capable of predicting the response of lateral strains correctly due to incorporating the initial Poisson's ratio and the final converged dilation rate only. Further, the proposed method seems to have greater benefits in other applications by the use of the fundamental principles of mechanics.

• 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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• 2009.05a
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• pp.45-46
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• 2009

The main objective of this study is to suggest section design method of CFFT(Concrete Filled FRP Tube) structures which are considered of confined effect by FRP tube and using high strength concrete and PS strands for pier. It may be stated that the proposed method may be implemented as a rational and practical approach for CFFT section design.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.1
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• pp.103-111
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• 2011

This paper estimated the structural behavior of recycled aggregate concrete confined with spiral reinforcement. The main test parameter was designed to be the type of aggregates and the steel ratio of spirals. A total of 18 specimens were cast and tested in this study. All the specimens had a diameter of 150mm and a height of 300mm. The specimens can be divided into two groups, based on the type of coarse aggregate used. The ratio of spiral reinforcement was varied from 0 % to 1.75%. To measure the axial and lateral deformations of the specimens, a total of six linear variation displacement transducers (LVDTs) were installed at each specimen. Furthermore strain gauges were also attached to the steel spirals to obtain the strain of spiral reinforcements. From the experimental results, the structural performance of recycled aggregate concrete specimens confined by steel spirals was similar to that of natural aggregate concrete specimens regardless of the ratio of spiral reinforcement.

• 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 the Korea institute for structural maintenance and inspection
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• v.11 no.2
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• pp.125-133
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• 2007

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 curve is required for CFS-confined concrete. In this paper, uniaxial compression test on short RC column with circular section was performed. To evaluate the effect of confinement on the stress-strain relationship of CFS-confined concrete, CFS area ratio, spiral area ratio, and concrete compressive strength are considered as the test variables. Experiment results indicate that CFS jacketing significantly enhances strength and ductility of concrete. In addition, the CFS-jacketed specimens with the spiral steel show the lower load increasement ratio than those without the spiral steel.