• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2005년도 학술발표회 논문집
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• pp.345-352
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• 2005

The purpose of this study is to analyze the stress-strain behavior of confined concrete columns with rectangular section. Uniaxial concentric loading tests of nineteen concrete columns with rectangular section ($150{\times}100$, $250{\times}100$, $350{\times}100\;mm$) were conducted. The main variables are transverse reinforcement volumetric ratio and spacing, cross tie arrangement, cross-section aspect ratio, and concrete strength. From the present experiments, it was found that the increase of transverse reinforcement ratio increases the maximum stress and ductility ratio and the reduction of the spacing of transverse reinforcement also increases the ductility and effective confinement. The increase of the aspect ratio of the cross-section does not influence much the stress-strain behavior of rectangular columns within the aspect ratio range of 3.5. The effect of concrete strength on ductility is also discussed.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.487-492
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• 2003

High-strength concrete(HSC) is a new construction material with enormous potential. Structures using high-strength concrete are to be coming more and more popular. But high-strength reinforced concrete columns show brittle behavior. It, therefore, is necessary to improve the ductility of HSC members. The purpose of this study is to investigate the ductility and strength of high-strength columns with variable lateral confinement under concentric axial load. Five HSC columns with compressive strength 68㎫ are designed with variable lateral confinements such as carbon fiber sheet(CFS), glass fiber sheet(GFS), and metal lath. Test results indicate that specimen confined by CFS show 11% higher maximum strength, 2.74 times ductility than A specimen using hoop. On comparing with the specimen A and B confined metal lath instead of hoop, strength decrease of 3%, and ductility increase of 1.21 times were observed.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.937-942
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• 2003

Three series of 36 short circular columns confined by wraps, full shells and partial shells were tested by varying the thickness of GFRP laminates. An assessment of the effectiveness of the existing models on confinement of concrete columns with FRP was made for present tests. Test results indicated significant increases in strength and deformability compared with those in unconfined concrete, particularly warp and full shell confinement. Existing predictive equations for peak strength and strain of confined concrete showed a large scatter and varied considerably, resulting from the realistic fracture strains of FRP nor considered.

• Structural Engineering and Mechanics
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• 제65권6호
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• pp.679-687
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• 2018

In composite materials technology, the fiber-reinforced polymers (FRP) have opened up new horizons in infrastructural engineering field for strengthening existing structures and components of structure. The Carbon fiber reinforced polymer (CFRP) sheets are well suited for RC columns to this application because of their high strength to weight ratio, good fatigue properties and excellent resistance to corrosion. The main focus of present experimental work is to investigate effect of shapes on axial behavior of CFRP wrapped RC columns having same cross-sectional area and slenderness ratio. The CFRP volumetric ratio and percentage of steel are also adopted constant for all the test specimens. A total of 18 RC columns with slenderness ratio four were cast. Nine columns were control and the rest of nine columns were strengthened with one layer of CFRP wrap having 35 mm of corner radius. Columns confined with CFRP wrap were designed using IS: 456:2000 and ACI 440.2R.08 provisions. All the test specimens were loaded for axial compression up to failure and failure pattern for each shaped column was investigated. All the experimental results were compared with analytical values calculated as per the ACI-440.2R-08 code. The test results clearly demonstrated that the axial behavior of CFRP confined RC columns is affected with the change in shapes. The axial deformation is higher in CFRP wrapped RC circular column as compared to square and rectangular columns. Stress-strain behaviour revealed that the yield strength gained from CFRP confinement was significant for circular columns as compare to square and rectangular columns. This behaviour may be credited due to effect of shape on lateral deformation in case of CFRP wrapped circular columns at effective confinement action.

• Computers and Concrete
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• 제25권5호
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• pp.383-400
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• 2020

Due to higher stiffness to weight, higher corrosion resistance, higher strength to weight ratios and good durability, concrete composite structures provide many advantages as compared with conventional materials. Thus, they have wide applications in the field of concrete construction. This research focuses on the structural behavior of steel-tube CFRP confined concrete (STCCC) columns under axial concentric loading. A nonlinear finite element analysis (NLFEA) model of STCCC columns was simulated using ABAQUS which was then, calibrated for different material and geometric models of concrete, steel tube and CFRP material using the experimental results from the literature. The comparative study of the NLFEA predictions and the experimental results indicated that the proposed constitutive NLFEA model can accurately predict the structural performance of STCCC columns. After the calibration of NLFEA model, an extensive parametric study was performed to examine the effects of different critical parameters of composite columns such as; (i) unconfined concrete strength, (ii) number of CFRP layers, (iii) thickness of steel tube and (iv) concrete core diameter, on the axial load capacity. Furthermore, a large database of axial strength of 700 confined concrete compression members was developed from the previous researches to give an analytical model that predicts the ultimate axial strength of composite columns accurately. The comparison of the predictions of the proposed analytical model was done with the predictions of 216 NLFEA models from the parametric study. A close agreement was represented by the predictions of the proposed constitutive NLFEA model and the analytical model.

• Structural Engineering and Mechanics
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• 제77권2호
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• pp.179-196
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• 2021

Experimental investigations on the seismic behaviors of the PVC-FRP Confined Reinforced Concrete (PFCRC) columns under low cyclic loading are carried out and two variable parameters including CFRP strips spacing and axial compression ratio are considered. The PFCRC column finally fails by bending and is characterized by the crushing of concrete and yielding of the longitudinal reinforcement, and the column with a high axial compression ratio is also accompanied by the cracking of the PVC tube and the fracture of CFRP strips. The hysteretic curves and skeleton curves of the columns are obtained from the experimental data. With the increase of axial compression ratio, the stiffness degradation rate accelerates and the ductility decreases. With the decrease of CFRP strips spacing, the unloading sections of the skeleton curves become steep and the ductility reduces significantly. On the basis of fiber model method, a numerical analysis approach for predicting the skeleton curves of the PFCRC columns is developed. Additionally, a simplified skeleton curve including the elastic stage, strengthening stage and unloading stage is suggested depending on the geometric drawing method. Moreover, the loading and unloading rules of the PFCRC columns are revealed by analyzing the features of the skeleton curves. The quantitative expressions that are used to predict the unloading stiffness of the specimens in each stage are proposed. Eventually, an analytical model for the PFCRC columns under low cyclic loading is established and it agrees well with test data.

• Earthquakes and Structures
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• 제7권4호
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• pp.527-552
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• 2014

The development of modern concrete technology makes it much easier to produce high-strength concrete (HSC) or ultra-high-strength concrete (UHSC) with high workability. However, the application of this concrete is limited in practical construction of traditional reinforced concrete (RC) structures due to low-ductility performance. To further push up the limit of the design concrete strength, concrete-filled-steel-tube (CFST) columns have been recommended considering its superior strength and ductility performance. However, the beneficial composite action cannot be fully developed at early elastic stage as steel dilates more than concrete and thereby reducing the elastic strength and stiffness of the CFST columns. To resolve this problem, external confinement in the form of steel rings is proposed in this study to restrict the lateral dilation of concrete and steel. In this paper, a total of 29 high-strength CFST (HSCFST) columns of various dimensions cast with concrete strength of 75 to 120 MPa concrete and installed with external steel rings were tested under uni-axial compression. From the results, it can be concluded that the proposed ring installation can further improve both strength and ductility of HSCFST columns by restricting the column dilation. Lastly, an analytical model calculating the uni-axial strength of ring-confined HSCFST columns is proposed and verified based on the Von-Mises and Mohr-Coulomb failure criteria for steel tube and in-filled concrete, respectively.

• Steel and Composite Structures
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• 제23권2호
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• pp.229-238
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• 2017

This paper presents a combined numerical and theoretical study on the composite action between steel and concrete of circular steel tube confined concrete (STCC) stub columns under axial compressive loading with a full theoretical elasto-plastic model and finite element (FE) model in comparison with experimental results. Based on continuum mechanics, the elasto-plastic model for STCC stub columns was established and the analysis was realized by a FORTRAN program and the three dimensional FE model was developed using ABAQUS. The steel ratio of the circular STCC columns were defined in range of 0.5% to 2% to analyze the composite action between steel tube and concrete, and make a further study on the advantages of the circular STCC columns. By comparing the results using the elasto-plastic methods with the parametric analysis result of FE model, the appropriate friction coefficient between the steel tube and core concrete was defined as 0.4 to 0.6. Based on ultimate balance theory, the formula of ultimate load capacity applying to the circular STCC stub columns was developed.

• Steel and Composite Structures
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• 제45권1호
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• pp.51-66
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• 2022

This paper presents the axial compression behavior of partially encased composite (PEC) columns using H-shaped structural steel. In the experimental program, a total of eight PEC columns with H-shaped steel sections of different flange and web slenderness ratios were tested to investigate the interactive mechanism between steel and concrete. The test results showed that the PEC columns could sustain the load well beyond the peak load provided that the flange slenderness ratio was not greater than five. In addition, the previous analytical model was extended to predict the axial load-strain relationships of the PEC columns with H-shaped steel sections. A good agreement between the predicted load-strain relationships and test data was observed. Using the analytical model, the effects of compressive strength of concrete (21 to 69 MPa), yield strength of steel (245 to 525 MPa), slenderness ratio of flange (4 to 10), and slenderness ratio of web (10 to 25) on the interactive mechanism (K_h = confinement factor for highly confined concrete and K_w = reduction factor for steel web) and ductility index (DI = ratio between strain at peak load and strain at proportional load) were assessed. The numerical results showed that the slenderness of steel flange and yield strength of steel significantly influenced the compression behavior of the PEC columns.

• 한국지진공학회논문집
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• 제7권1호
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• pp.1-7
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• 2003

탄소섬유튜브는 기존의 콘크리트 기둥에 강도와 연성을 제공하여 길이방향 및 횡방향 철근을 대신할 수 있다. 본 연구에서는 탄소섬유튜브에 의해 구속된 각형 콘크리트의 축하중에 대한 실험 및 해석적 연구를 수행하였다. 탄소섬유튜브는 길이방향에 대하여 90$^{\circ}$$\pm$30$^{\circ}$, 90$^{\circ}$$\pm$45$^{\circ}$로 섬유의 방향을 조합하여 필라멘트 와인딩 방법으로 제작하였다. 10,000kN UTM을 이용하여 단조축하중을 재하하였다. 섬유의 방향, 튜브의 두께에 따른 횡구속된 콘크리트 기둥의 응력-변형률 관계를 고찰하였다. 탄소섬유튜브에 의해 횡구속된 콘크리트의 압축강도와 연성을 예측하기 위하여 제안된 실험식은 실험결과를 적절히 예측하는 것으로 나타났다.