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Carbon fiber reinforced polymer (CFRP) has many advantages, such as light weight, high strength, and excellent corrosion resistance. In this paper, the experimental research of the square steel tube reinforced by carbon fiber reinforced polymer was performed, and its ultimate bearing capacity formula was derived. The tests were based on the previous results of our research group. Six sets of the test are performed by altering two-layer-CFRP and the eccentricity. The test results demonstrated that CFRP improved the ultimate bearing capacity of square steel tubes. As the number of layers of CFRP increased, the growth rate of bearing capacity gradually declined, and reinforcement of CFRP on specimens of large eccentricity was significantly effective than that of small eccentricity one. After longitudinal CFRP was stuck, a circumferential layer of CFRP in the middle of the square steel tube can improve the reinforcement effect. This paper referred to the existing codes and took the idea of area substitution to derive the ultimate bearing capacity formula of the steel tube reinforced by CFRP. The calculated values of the formula were compared with those of the experiment, and the difference is within the range, which proves the rationality of the derived formula. [ABSTRACT FROM AUTHOR]

Based on the energy method, this article presents a theoretical study on the elastic local buckling of steel plates in rectangular concrete-filled steel tubular columns with binding bars subjected to eccentric compression. The formulas for elastic local buckling strength of the steel plates in eccentrically loaded rectangular concrete-filled steel tubular columns with binding bars are derived, assuming that the loaded edges are clamped and the unloaded edges of the steel plate are elastically restrained against rotation. Then, the experimental results are compared with these formulas, which exhibits good agreement. Subsequently, the formulas are used to study the elastic local buckling behavior of steel plates in rectangular concrete-filled steel tubular columns with binding bars under eccentric compression. It is found that the local buckling stress of steel plates in eccentrically loaded rectangular concrete-filled steel tubular columns with binding bars is significantly influenced by the stress gradient coefficient, width-to-thickness ratio, and the longitudinal spacing of binding bars. With the decrease of width–thickness ratios or the longitudinal spacing of binding bars or with the increase of the stress gradient coefficient, the local buckling stress increases. Furthermore, the influence of the longitudinal spacing of binding bar is more significant than the stress gradient coefficients. Finally, appropriate limitation for depth-to-thickness ratios (D / t), width-to-thickness ratios (B / t), and binding bar longitudinal spacing at various stress gradient coefficients (α 0) corresponding to different cross-sectional aspect ratios (D / B) are suggested for the design of rectangular concrete-filled steel tubular columns with binding bars under eccentric compression. [ABSTRACT FROM AUTHOR]

In this study, the mechanical properties and failure characteristics of steel reactive powder concrete columns with different strength grades were investigated through compression testing. Six steel reactive powder concrete columns were tested; three columns underwent axial compression testing and three columns underwent eccentric compression testing. The results of the axial compression testing showed that steel and reactive powder concrete could work cooperatively at the initial stage, and the final column failure mode was primarily splitting failure at the end of the column, with the formation of a main crack in the longitudinal direction extending to the middle of the column. The results of the eccentric compression testing showed that the eccentrically loaded steel reactive powder concrete columns had comparatively strong deformability. The columns presented ductile failure mode under the eccentric load with 0.2 eccentricity. The final failure of the column involved a sudden increase in the horizontal crack width on the tension side, the steel flange on the tension side reached the yield state, the reactive powder concrete in the middle of the compressive side was crushed, and the reactive powder concrete surface layer burst open and partially spalled off. According to the test results and with reference to the relevant standards, equations for calculating the approximate ultimate bearing capacities of axially and eccentrically compressed reactive powder concrete columns were proposed. [ABSTRACT FROM AUTHOR]

Engineered cementitious composites have the characteristics of tensile strain hardening and multiple cracking. Substituting concrete with engineered cementitious composites can effectively avoid the cracking and durability problems induced by concrete brittleness. In this study, four steel-reinforced columns with various matrix types and load eccentricities were tested under eccentric compression. Test results indicated that steel-reinforced engineered cementitious composite columns exhibited a larger load-carrying capacity, higher ductility, better crack control ability, and damage tolerance, compared to reinforced concrete columns. All columns finally failed in compression as manifested by matrix crushing. However, the failure patterns between steel-reinforced engineered cementitious composite columns and reinforced concrete columns were extremely different. Significant concrete spalling appeared in the reinforced concrete columns, while no sign of engineered cementitious composite spalling was observed in the steel-reinforced engineered cementitious composite columns owing to the fiber bridging effect of engineered cementitious composite. The maximum crack width in reinforced concrete column increases almost linearly with the applied load and reaches 2 mm at most just prior to attaining the ultimate strength, while the maximum crack width in the steel-reinforced engineered cementitious composite column first increases and thereafter remains constant at approximately 60 μm with an increasing compression load. In addition to experimental work, a finite element model was proposed to predict the load–deformation response of the steel-reinforced engineered cementitious composite column. The prediction results are in close agreement with the test data. Finally, parametric studies were conducted to further illustrate the effects of matrix ductility and load eccentricity on the load–deformation curves, strain contour, and moment–load interaction curves of the columns. [ABSTRACT FROM AUTHOR]

The eccentric compressive behavior of 18 recycled aggregate concrete columns after freezing and thawing cycles were investigated. The effect of the number of freezing and thawing cycles, the replacement ratio of recycled coarse aggregate, and the eccentricity of axial loading on the eccentric compressive behavior of columns was analyzed. The results show that the strain distribution along the depth of cross section of columns was plane during the eccentric compression test after freezing and thawing cycles. With the increase in the freezing and thawing cycles and the replacement ratio of recycled coarse aggregate, the failure modes of partial specimens turned from ductile tension failure to brittle compression failure. Two existing design methods for calculating the bearing capacity of conventional concrete columns subjected to eccentric compressive loading were verified to be effective for evaluating that of recycled aggregate concrete columns after limited freezing and thawing cycles. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced polymer tubes filled with steel-reinforced high-strength concrete are proposed as glass fiber-reinforced polymer-steel-reinforced high-strength concrete composite members. Eccentric compression is a typical loading scenario for such column members in practice. Experimental investigation on eight glass fiber-reinforced polymer tubes filled with steel-reinforced highstrength concrete columns subjected to eccentric compression was conducted. The effects of fiber orientation, thickness of glass fiber-reinforced polymer tube, slenderness ratio of columns, and loading eccentricity were investigated. It was found that the compression bearing capacity of glass fiber-reinforced polymer-steel-reinforced high-strength concrete columns increased with the decrease in the fiber tangle angle and the increase in the thickness of the glass fiber-reinforced polymer tube but reduced with the increase in the eccentricity and the slenderness ratio. Corresponding formulas were developed based on the nonlinear full-process analysis theory to describe the compression behavior of glass fiber-reinforced polymer-steel-reinforced high-strength concrete under eccentric loading. Good agreement was found through the comparison between the theoretical and the experimental results. The validated modeling approach was, therefore, employed to develop a parametric analysis that can be used to provide valuable guidance for practical application and further research on such structural members. [ABSTRACT FROM AUTHOR]

FRP-Concrete-Steel Double-Skin Tubular Columns (DSTCs) are a new form of hybrid columns which effectively combines the advantages of the constituent materials. A DSTC consists of an outer fibre-reinforced polymer (FRP) tube and an inner steel tube with the gap between filled with concrete. This paper presents the first-ever large-scale tests on slender DSTCs subjected to eccentric compression. The major parameters examined include the load eccentricity and the confinement stiffness of the FRP tube. Test results show that slender DSTCs possess good ductility under eccentric compression. Larger load eccentricity results in lower axial load capacity and higher deformability; larger confinement stiffness of the FRP tube results in larger axial load capacity and deformability. The axial strain distribution of a DSTC section subjected to eccentric compression generally conforms to the plane section assumption, but the ultimate axial strain of concrete is increased as a result of eccentric compression. [ABSTRACT FROM AUTHOR]

Hybrid FRP-concrete-steel double-skin tubular columns (DSTCs) are a new form of hybrid columns recently proposed by the third author. The new column consists of an inner steel tube and an outer FRP tube, with the space between them filled with concrete. The new column possesses many advantages over existing columns including its good ductility, corrosion resistance and ease for construction. This paper presents the results of an experimental study on the behavior of the new hybrid DSTCs subject to eccentric compression as well as results from a corresponding theoretical model using the fiber element approach. A so-called 'variable confinement model' was adopted in the theoretical analysis for the concrete in the hybrid DSTCs, to account for the effect of strain gradient on the confinement effectiveness. The theoretical model was shown to provide accurate predictions of the test results, and was used in a subsequent parametric study. [ABSTRACT FROM AUTHOR]