Static And Seismic Behavior Of Steel Tube Confined Concrete Short Columns

The experimental study and theoretical analysis have been conducted for the behavior of the tubed short columns in the thesis, including the axial static behavior of circular and square tubed short columns subjected to axial compressive load, as well as the seismic behavior of circular and square tubed short and ultra-short columns subjected to constant axial load and cyclic lateral load. The following is a summary of the main works finished.An experimental research was executed to investigate the behavior and farilure modes of cicular tubed concrete stub column under concentrically load. Ten circular tubed reinforced concrete (CTRC) and four circular tubed steel reinforced concrete (CTSRC) stub columns were tested. The effect of diameter to thickness ratio of the tubes, the embedded reinforcement and profile steel were studied. Vertical load vs vertical deformation (and horizontal deformation) curves and vertical load vs steel-tubestrains were experimentally measured. According to test results, mechanical model of the circular tubed concrete(CTC) columns at the maximum capacity was established. The mechanical equilibrium equations and the stress state of steel tubes were derived based on the model. A three-dimensional finite element method (FEM) model was developed by using ABAQUS software to analyze the influence of the friction coefficient to the axial bearing capacity. The equations for the prediction of the axial bearing strength of circular tubed concrete stub columns were also proposed based on the experiment, theoretical analysis and FEM analysis.The seismic behavior of circular tubed reinforced concrete (RC) short short beam-columns has been investigated by testing two short specimens and two ultra-short specimens subjected to a constant axial compression combined with a lateral cyclic loading. The seismic shear failure mode of the circular tubed RC beam-columns has been experimentally investigated for the first time. The lateral force-displacement hysteretic response and lateral force vs. steel-tube strains were experimentally measured. The hysteretic behavior, horizontal bearing capacity, plastic deformation and energy dissipation capacity were analyzed according to tests results. Elasto-plastic analysis on the steel tube was employed to study the mechanism of the beam-columns subjected to combined constant axial compression and lateral cyclic loading. The failure mechanism and the composite response of short beam-columns and super-short beam-columns with different failure modes were analyzed. A seismic shear mechanical model was proposed for circular steel tubed beam-columns. The equations for the prediction of the seismic shear strength of circular tubed concrete beam-columns were also proposed based on the experimental results, theoretical analysis and FEM analysis.An experimental program was developed to examine the behavior and farilure modes of square tubed concrete stub column under axial compressive load. Nine square tubed RC (STRC) and for square tubed SRC (STSRC) stub columns were tested. The effect of breadth to thickness ratio of the tubes, the embedded reinforcement and profile steel were studied. Vertical load vs vertical deformation (and horizontal deformation) curves and vertical load vs steel tube strains were experimentally measured. The influence of the friction coefficient and confining size effect on axial bearing capacity was investgated by FEM. According to test results, the effective section confining model of square tube concrete was developed. The equations for the prediction of the axial load strength of square tubed concrete stub columns were also proposed based on the experiments, theoretical analysis and FEM analysis.The seismic behavior of square tubed RC ultra-short beam-columns has been investigated by testing two short specimens with stiffeners and two ultra-short specimens without stiffener subjected to a constant axial compression combined lateral cyclic loading. The lateral force-displacement hysteretic response and lateral force vs steel tube strains were experimentally measured. The hysteretic behavior, horizontal bearing capacity, plastic deformation and energy dissipation capacity were analyzed according to tests results. The steel-tubes were analyzed by elasto-plastic method to study the mechanism of the beam-columns subjected to combined constant axial compression and lateral cyclic load. The failure mechanism and the composite response of short beam-columns and ultra-short beam-columns of different failure modes were analyzed. The influence of stiffeners on the composite response of steel tubes and concrete was also analyzed. The influence of friction coefficient and axial load ratio on shear behavior(shear capacity) were investigated by using finite element method. A seismic shear mechanical model was proposed for square steel tubed beam-columns. The equations for the prediction of the seismic shear strength of square tubed concrete beam-columns were also proposed based on the experiments, theoretical analysis and FEM analysis.The following is a summary of the main creative points of the thesis.1. The mechanical model of circular tubed concrete(CTC) columns at the maximum capacity was established. The mechanical equilibrium equations and the stress state of steel tubes were derived based on the model. A three-dimensional finite element method (FEM) model was developed with the ABAQUS software to analyze the influence of the friction coefficient and shear limit on axial load behavior and axial bearing capacity. The equations for the prediction of the axial load strength of circular tubed concrete stub columns were also proposed.2. The seismic shear failure mode of circular tubed RC beam-columns has been experimentally investigated for the first time. The failure mechanism and the composite response of short beam-columns and super-short beam-columns of different failure modes were analyzed. The influence of friction coefficient and axial load ratio on shear behavior(shear capacity) were investigated by using finite element method. A seismic shear mechanical model was proposed for circular steel tubed beam-columns. The equations for the prediction of the seismic shear strength of circular tubed concrete beam-columns were also proposed.3. The influence of longitudinal reinforcement buckling on the axial load behavior and axial strength was experimentally studied. The influence of the friction coefficient and confining size effect on axial bearing capacity was investigated by FEM. The effective section confining model of square tube concrete was developed. The equations with clear physical significance for the prediction of the axial load strength of square tubed concrete stub columns were also proposed.4. The steel-tubes were analyzed by elasto-plastic method to study the mechanism of the beam-columns subjected to a constant axial compression combined lateral cyclic loading. The failure mechanism and the composite response of short beam-columns and ultra-short beam-columns of different failure modes were analyzed. The influence of stiffeners on the composite response of steel tube and concrete was also analyzed. The influence of friction coefficient and axial load ratio on shear behavior was investigated by using finite element method. A seismic shear mechanical model was proposed for square steel tubed beam-columns. The equations for the prediction of the seismic shear strength of square tubed concrete beam-columns were also proposed based on the experiments, theoretical analysis and FEM analysis.