The Static Behavior Of Steel Tube Confined Concrete Columns Under Axial And Eccentric Loading

A steel-tube-confined concrete column (STC) is a new type of composite column based on the concepts of concrete-filled-steel-tube columns and steel-reinforced concrete column. STCs have the advantages of high bearing capacity, good ductility, good fire resistance, and convenient construction. Research on STCs began in recent years in China, with the initial focus being only on short columns under concentric loading. Research on slender STCs under eccentric loading has not previously been carried out, despite this being the more common engineering application. This paper describes an experimental study and theoretical analysis conducted on the behavior of slender STCs under eccentric loading.An experimental study was conducted to investigate the behavior of circular tube-reinforced concrete columns (CTRC). Eight circular tube-reinforced concrete specimens were tested under concentric loading, and16circular tube-reinforced concrete specimens were tested under eccentric loading. The main experimental parameters examined were the slenderness ratios of the columns, the eccentricity of the loading, and the steel tube confinement mode. The failure modes of the columns were investigated. The load–displacement curves of the columns and the load–stress curves of the steel tubes were measured experimentally. A mechanical model for the behavior of a slender CTRC under eccentric loading was developed based on the test results. A three-dimensional (3D) finite element method (FEM) model was also developed using ABAQUS to analyze the behavior of a slender CTRC under eccentric loading.A second experimental study was conducted to investigate the behavior of square tube-reinforced concrete columns (STRC). Eight square tube-reinforced concrete specimens were tested under concentric loading, and16square tube-reinforced concrete specimens were tested under eccentric loading. The main experimental parameters examined were the slenderness ratios of the columns, the eccentricity of the loading, and the steel tube confinement mode. The failure modes of the columns were investigated. The load–displacement curves of the columns and the load–stress curves of the steel tubes were measured experimentally. A mechanical model for the behavior of a slender STRC under eccentric loading was developed based on the test results. A3D FEM model was also developed using ABAQUS to analyze the behavior of a slender STRC under eccentric loading.A third experimental study was conducted to investigate the behavior of circular tubed-steel concrete columns (CTSRC). Twelve short circular tubed-steel concrete column specimens and12slender circular tubed-steel concrete column specimens were tested. The main experimental parameters examined were the slenderness ratios of the columns, the eccentricity of the loading, the steel tube confinement mode, and whether or not a shear key was present. The failure modes of the columns were investigated. The load–displacement curves of the columns and the load–stress curves of the steel tubes were measured experimentally. A mechanical model for a slender CTSRC under eccentric loading was developed based on the test results. A3D FEM model was also developed using ABAQUS to analyze the behavior of a slender CTSRC under eccentric loading.A fourth experimental study was conducted to investigate the behavior of square tubed-steel concrete columns (STSRCs). Twelve short square tubed-steel concrete column specimens and12slender square tubed-steel concrete column specimens were tested. The main experimental parameters examined were the slenderness ratios of the columns, the eccentricity of the loading, the steel tube confinement mode, and whether or not a shear key was present. The failure modes of the columns were investigated. The load–displacement curves of the columns and the load–stress curves of the steel tubes were measured experimentally. A mechanical model for the behavior of a slender STSRC under eccentric loading was developed based on the test results. A3D FEM model was also developed using ABAQUS to analyze the behavior of a slender STSRC under eccentric loading.Based on Mander’s confined concrete model, the load–displacement curves were computed using the fiber method. The calculated results agreed well with the experimental data. The equivalent rectangular stress was obtained using this model. Based on the theory of energy, the confined concrete ultimate strain was obtained. A method for calculating the section bearing capacity of a tube-reinforced concrete column under eccentric loading can be established using the equivalent rectangular stress and the confined concrete ultimate strain. The buckling factor for a slender column was obtained using the tangent modulus method. The magnifying coefficient of eccentricity can be obtained based on reinforced concrete design principles. Using the buckling factor for a slender column and the magnifying coefficient of eccentricity, we can obtain the bearing capacity of the member.Based on the hypothesis about the plastic behavior of an entire section presented in the European standard Eurocode4, the load–moment (N–M) curve of a CTSRC (STSRC) can be determined using the fiber method. A simplified method for calculating the section bearing capacity was employed, based on the four key points of the N–M curve. The N–M curve of a CTSRC (STSRC) member can be determined using the reduction bending moment method. In the same way, a simplified method for calculating the member bearing capacity was employed, based on the four key points of the N–M curve of the member.