Mechanical Behavior Of T-shaped Composite Columns

Compared with traditional columns with square or rectangular cross-sections, special-shaped columns (T-shaped, L-shaped and cross-shaped columns) provide prominent architectural functions with more regular indoor space, variety of furniture layout and space efficiency. Engineering practices at present is the special-shaped reinforced concrete (RC) column. However, in respect to applicable building height and seismic fortification intensity, traditional special-shaped RC columns have strict limitations in seismic behavior which hampers their further generalization and application. To improve the seismic behavior of the special-shaped column, the dissertation concentrated to T-shaped cross-sections, putting forward three innovative kinds of steel-concrete composite columns: T-shaped stiffened concrete-filled steel tube (CFST) columns, T-shaped stiffened steel tube confined concrete columns and T-shaped latticed circular tubes reinforced concrete columns. In order to restrain or prevent the local buckling of T-shaped tube and enhance the constraint effect on the core concrete, the reinforcement stiffener has been put forward. Test and theoretical analysis were carried out on the axial, eccentric and combined compressive-bending mechanical behavior of the T-shaped steel-concrete composite columns. Furthermore, based on the axial behavior, association of the axial, eccentric and combined compressive-bending behavior was studied. The research work consists of the following four parts:(1) Experimental research and theoretical study on the axial mechanical behavior of square stiffened CFST stubs have been performed. Steel reinforcement/strip stiffeners were put forward to restrain the local buckling of steel tubes, to prepared being applied in the T-shaped column. Axial behavioral experiment of the reinforcement/strip stiffened and non-stiffened square CFST specimens was carried out to investigate the influence of the stiffeners on the mechanical properties of square CFST and on the local buckling of steel tubes. Experimental results show that reinforcement/strip stiffeners can restrain the tube's local buckling and improve the specimens'resistance and ductility. The distribution law of constraint concrete in square stiffened CFST was proposed on the basis of the experiments and superposition principle. Both the constraint concrete's compressive strength and the stiffened tube's buckling resistance have been studied, and the corresponding calculation suggestions were provided. The rationality and reliability of the theoretical work was verified by the experimental results, based on which, parametric analysis was conducted and simplified calculation formulas for resistance of the stiffened square CFST stub was put forward.(2) Experimental research and theoretical study on the axial mechanical behavior of T-shaped composite stubs have been conducted. Axial behavioral experiment of 8 T- shaped specimens was carried out. The category of the specimens includes the RC specimen, the non-stiffened CFST specimen, the reinforcement stiffened CFST specimen, the steel tube confined concrete specimen and the latticed circular tubes reinforced concrete specimen. The effects of specimen category and stiffener type were intensively investigated. Experimental results indicate that T-shaped composite columns gain improved strength and ductility over traditional RC columns. The distribution law of constraint concrete in stiffened T-shaped CFST was proposed on the basis of the experiments and superposition principle. The calculation methods of the constraint concrete'compressive strength and the stiffened steel plate's buckling resistance were put forward. Parametric analysis was conducted and simplified calculation formulas for the resistance of the T-shaped stiffened CFST stub was provided.(3) Experimental and theoretical research on the mechanical behavior of T-shaped composite columns subjected to eccentric loads was carried out. Eccentric loading tests were conducted on 8 T-shaped specimens includes the RC specimen, the non-stiffened CFST specimen, the reinforcement stiffened CFST specimen, and the latticed circular tubes reinforced concrete specimen. The influences of specimen category, stiffener type and eccentricity were investigated. It is shown that, compared with the eccentrically loaded RC specimen, both the enhanced resistance and ductility of the steel-concrete composite specimens can be gained. Simulation on the stiffened CFST and the latticed circular tubes reinforced concrete columns was performed based on the fiber-based model. Two loading paths have been paralleled considered in the self-developed program. The rationality and reliability of the theoretical work was verified by the experimental results and parametric analysis was conducted, based on which, the calculation method of the N-M resistance correlation curves of T-shaped stiffened CFST stubs and columns was put forward.(4) Experimental and theoretical research on the seismic behavior of T-shaped composite columns subjected to combined compression - bending cyclic loads were completed. Cyclic loading tests were carried out on 10 T-shaped specimens which included the RC specimen, the non-stiffened CFST specimen, the reinforcement stiffened CFST specimen, the steel tube confined concrete specimen, and the latticed circular tubes reinforced concrete specimen. The mechanical differences due to specimen category, stiffener type and axial compressive ratio were investigated. The experiment showed that, compared with those of the RC columns, the resistance, ductility and energy dissipation capacity of composite specimens subjected to cyclic loads can be improved. Based on the experimental research, a numerical program of T-shaped stiffened CFST columns and latticed circular tubes reinforced concrete columns subjected to combined compression - bending cyclic loads was compiled, in which the contraflexure point's movement was considered. The rationality and reliability of the theoretical work was verified by the experimental results and parametric analysis was conducted, based on which, the restoring force model for the T-shaped composite columns was put forward.