• Computers and Concrete
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• v.8 no.5
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• pp.597-616
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• 2011

With respect to rehabilitation, strengthening and retrofitting of existing and deteriorated columns in buildings and bridges, CFRP sheets have been found effective in enhancing the performance of existing RC columns by wrapping and bonding CFRP sheets externally around the concrete. Concrete columns and piers that are confined by both lateral steel reinforcement and CFRP are sometimes referred to as "hybrid" concrete columns. With the availability of experimental data on concrete columns confined by steel reinforcement and/or CFRP, the study presents modeling using artificial neural networks (ANNs) to predict the compressive strength of hybrid circular RC columns. The prediction of the ultimate confined compressive strength of RC columns is very important especially when this value is used in estimating the capacity of structures. The present ANN model used as parameters for the confining materials the lateral steel ratio (${\rho}_s$) and the FRP volumetric ratio (${\rho}_{FRP}$). The model gave good predictions for three types of confined columns: (a) columns confined with steel reinforcement only, (b) CFRP confined columns, and (c) hybrid columns confined by both steel and CFRP. The model may be used for predicting the compressive strength of existing circular RC columns confined with steel only that will be strengthened or retrofitted using CFRP.

• Steel and Composite Structures
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• v.21 no.2
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• pp.411-427
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• 2016

While the cyclic behaviour of fiber-reinforced polymer (FRP)-confined columns is studied rather extensively, the cyclic response especially the energy dissipation of FRP-confined damaged and undamaged square RC columns is not yet fully understood. In this paper, an experimental and numerical investigation was conducted to study the cyclic behavior of two different types of Carbon FRP (CFRP)-confined square RC columns: strengthened and repaired. The main variables investigated are initial damage, confinement of CFRP, longitudinal steel reinforcement ratio. The experimental results show that lower initial damage, added confinement with CFRP and longitudinal reinforcement enhance the ductility, energy dissipation capacity and strength of the columns, decrease the stiffness and strength degradation rates of all CFRP-confined square RC columns. Two hysteretic constitutive models were developed for confined damaged and undamaged concrete and cast into the non-linear beam-column fiber-based models in the software Open System for Earthquake Engineering Simulation (OpenSees) to analyze the cyclic behavior of CFRP-confined damaged and undamaged columns. The results of the numerical models are in good agreement with the experiments.

• Steel and Composite Structures
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• v.17 no.4
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• pp.431-452
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• 2014

The present study focuses on the mechanical behaviour of concrete filled double skin steel tubular (CFDST) stub columns confined by fiber reinforced polymer (FRP). A series of axial compression tests have been conducted on two CFDST stub columns, eight CFDST stub columns confined by FRP and a concrete-filled steel tubular (CFST) stub column confined by FRP, respectively. The influences of hollow section ratio, FRP wall thickness and fibre longitudinal-circumferential proportion on the load-strain curve and the concrete stress-strain curve for stub columns with annular section were discussed. The test results displayed that the FRP jacket can obviously enhance the carrying capacity of stub columns. Based on the test results, a new model which includes the effects of confinement factor, hollow section ratio and lateral confining pressure of the outer steel tube was proposed to calculate the compressive strength of confined concrete. Using the present concrete strength model, the formula to predict the carrying capacity of CFDST stub columns confined by FRP was derived. The theoretically predicted results agree well with those obtained from the experiments and FE analysis. The present method is also adapted to calculate the carrying capacity of CFST stub columns confined by FRP.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1997.04a
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• pp.182-190
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• 1997

A new method to prevent reinforced concrete columns from brittle failure. The method is called transversely reinforcing method in which only the critical regions are confined in steel tube. The steel tubes can change the failure mode of the latter columns from the shear to the flexure. The steel tubes also increase the compressive strength, shear strength and deformation capacity of the infilled concrete. The following conclusions are reached on bases of the study on the seismic performance of the high-strength RC rectangualr short columns confined in steel tube with shear span tho depth ratio of 2.0 The brittle shear failure of high-strength reinforced concrete short columns with large amount of longitudinal bars, which cannot prevented by using the maximum amount of welded hoops, can be prevented by using the steel tube which confines all the maximum amount of welded hoops, can be prevented by using the steel tube which confines all the concrete inclusive of cover concrete. High-strength RC short columns confined in rectangular steel tube provided excellent enhancement of seismic performance but, found that plastic buckling of the steel tube in the hinge regions tended to occur when the columns were subjected to large cyclic lateral displacements. In order to prevent the plastic buckling when the columns lies on large on cyclic lateral displacements, the steel ribs were used for columns. Tests have established that the columns provide excellent enhancement of seismic performance of inadequately confined columns.

• Advances in concrete construction
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• v.9 no.2
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• pp.125-137
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• 2020

As confining materials for concrete, steel and fibre-reinforced polymer (FRP) composites have important applications in both the seismic retrofit of existing reinforced concrete columns and in the new construction of composite structures. We present a comprehensive review of the axial stress-strain behaviour of the FRP-confined concrete column. Next, the mechanical performance of the hybrid FRP-confined concrete-steel composite columns are comprehensively reviewed. Furthermore, the results of FRP-confined concrete column experiments and FRP-confined circular concrete-filled steel tube experiments are presented to study the interaction relationship between various material sections. Finally, the combinations of material sections are discussed. Based on these observations, recommendations regarding future research directions for composite columns are also outlined.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.493-499
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• 1997

Objectives of this study is to investigate the behaviors of the confined concrete columns having different core sizes, lateral reinforcement ratios and spacing ratios by using the 3-dimensional analysis of confined concrete columns. In this paper, analyses are done by 3-D nonlinear finite element analysis considering continuum fracture and plasticity and then analysis results are compared with those of model tests. From the comparison, it is shown that the technique in this paper can be used effectively for the analysis of confined concrete columns.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.561-568
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• 1997

Conventional confinement reinforcement for rectangular columns consist of closely spaced perimeter hoops, overlapping hoops, and crossties. One of the potential alternatives to conventional reinforcement is a welded reinforcement grid, prefabricated to required size and volumetric ratio of transverse reinforcement. An experimental investigation was carried out to investigate the strength and deformability of reinforced concrete columns confined with welded reinforcement grids. The comparisons of the envelopes of experimental force-displacement hysteric relationships for columns confined by welded grids with analytically generated force-displacement curves for columns confined with conventional ties. In general, inelastic deformability beyond the peak, as indicate by the slope of the cuvers, was similar to those indicated by columns with conventional ties. The superior performance of columns with welded grids may be attributed to the improved confinement characteristics of grids associated with increased rigidity of welded ties.

• KCI Concrete Journal
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• v.12 no.1
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• pp.23-34
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• 2000

Experiments were carried out to investigate the seismic behaviors, such as lateral strength, ductility and energy-dissipation capacity. of high-strength concrete (HSC) square short column confined in thin steel shell. The primary objective of the study was to investigate the suitability of using HSC square columns confined in thin steel shell in region of moderate-to-high seismic risk. A total of six columns, consisting of two ordinarily reinforced concrete square short columns and four reinforced concrete square short columns confined in thin steel shell was tested. Column specimens, short columns in a moment resisting frame with girder. were tested under a constant axial and reversed cyclic lateral loads. To design the specimens. transverse reinforcing methods, level of axial load applied, and the steel tube width-thickness ratio (D/t) were chosen as main parameters. Test results were also discussed and compared in the light of improvements in general behaviors, ductility, and energy-absorption capacities. Compared to conventionally reinforced concrete columns, the HSC columns confined in thin steel shell had similar load-displacement hysteretic behavior but exhibited greater energy-dissipation characteristics . It is concluded that, in strong earthquake areas, the transverse reinforcing method by using a thin steel shell (D/t=125) is quite effective to make HSC short columns with very strong and ductile.

• Steel and Composite Structures
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• v.10 no.6
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• pp.501-516
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• 2010

This paper is aiming to study the performances of reinforced high-strength concrete (HSC) short columns confined with aramid fibre-reinforced polymer (AFRP) sheets. An experimental program, which involved 45 confined columns and nine unconfined columns, was carried out in this study. All the columns were circular in cross section and tested under axial compressive load. The considered parameters included the concrete strength, amount of AFRP layers, and ratio of hoop reinforcements. Based on the experimental results, a prediction model for the axial stress-strain curves of the confined columns was proposed. It was observed from the experiment that there was a great increment in the compressive strength of the columns when the amount of AFRP layers increases, similar as the ultimate strain. However, these increments were reduced as the concrete strength increasing. Comparisons with other existing prediction models present that the proposed model can provide more accurate predictions.

• Steel and Composite Structures
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• v.23 no.6
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• pp.669-682
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• 2017

The use of ultra high performance concrete (UHPC) in composite columns offers numerous structural benefits, and has received recent research attention. However, the information regarding the behavior of steel tube confined concrete (STCC) columns employing UHPC has been extremely limited. Thus, this paper presents an overview of previous experimental studies on circular STCC columns with taking into account various concrete strengths to point out their distinctive features. The effect of the confinement factor and the diameter to thickness ratio on both strength and ductility in circular STCC columns employing UHPC was investigated. The applicability of current design codes such as EC4, AISC, AIJ and some available analytical models for concrete confined by steel tube was also validated by the comparison of ultimate loads between the prediction and the test results of Schneider (2006) and Xiong (2012). To predict the stress-strain curves for confined UHPC in circular STCC stub columns, a simplified model was proposed and verified by the comparison with experimental stress-strain curves.