Experimental Research Of RC Special-shaped Columns Under Axial Force

Research has been conducted on members and frames with special-shaped columns with lots of achievements being made concerning flexural strength, shear strength, axial-compression ratio, ductility, joints and anti-seismic behavior. In order to determine the effect of stirrup character values on the confined concrete of special-shaped columns, 30 specimens, including十, T and L-shaped sections, were produced to do axial compression experiment.1. It is shown that the failure of those columns can be divided into two categories: axial compression failure and compression-shear failure. With the increase of stirrup ratio, the angle between failure section and horizontal section will gradually decrease, and the failure mode will turn into axial compression failure from compression-shear mode. Most of the bars will yield with no stirrups being destroyed.2. The ultimate strength and deformation will increase with better confinement of the concrete. the equations are established between stirrup character values and strain ductility coefficients of L,十and T-shaped columns . When the stirrup character values are between 0.5 and 2.5, The strain ductility coefficients of L,十and T-shaped columns are respectively 1.0~1.8,1.1~1.9 and 1.0~1.5.3. Based on the experimental data, the equation is established between increased value of peak strength or peak strain and stirrup ratio of L,十,T-shaped & rectangular columns. The increase for L and T-shaped columns is relatively small. For十-shaped columns, it is a moderate increase; While for rectangular ones, the increase is most remarkable.4. A formula between typical strainε0.85,ε0.5 and the stirrup character values under the condition of 0.85 f cc and 0.5 f cc is also set up. The formula for ductility coefficient of confined special-shaped columns is acquired with general agreement between calculated results and experimental data. The coefficients of十-shaped columns are higher than those of L and T shaped ones.5. To describe the stress-strain curve of confined concrete, a gray-optimum method is introduced for the upward section of the curves. The downward section is transferred into upward one through mathematical transition.6. A unified formula is applied to develop the stress-strain curves of various special-shaped columns so that it can really reflect the property of confined concrete. The general trend shows the best ductility of rectangular sections followed by十-shaped one and L&T sections.7. The bearing capacity formulas are established for L,T and十-shaped columns under axial loads. It is rather safe when the calculated values are relatively lower than the experimental ones.