Research On Flexural Stiffness Reduction Factor Of RC Column With Special-shaped Section

Special-shaped columns are generally referred to RC columns with T, L,十and Z special-shaped section. Frame structure with special-shaped columns is a special structure form in China. This structure especially fits the urban multistored buildings and small tall buildings with the characteristics of no indoor edges and light weight. More and more frame structure with special-shaped columns are applied in Chinese residential building.The reduced stiffness method had been adopted to consider nonlinear characteristics of reinforced concrete structure in concrete structure standards of the United States (ACI318-08) and Canada (CSA-A23.3-04). Concrete structure design code of China (GB 50010-2002) also accepted the reduced stiffness method as a supplementary method of considering the second-order effects problem when necessary. It shall be permitted to use the following properties for the members in the structure: 0.4 Ec I for beams, 0.6 Ec I for columns, and 0.45 Ec I for walls(uncracked and cracked). However, the concrete structure with specially shaped columns code of China still use amplified coefficients of eccentricity to consider nonlinearity characteristics of reinforced concrete sturcture with specially shaped columns.In order to simulate the nonlinear full response analysis of RC column with special-shaped section under biaxial bending and compression, the computer program ( M -Φprogram) is compiled by a numerical integral method using FORTRAN language. Based on the M -Φprogram, a load and lateral displacement relationship program ( P -Δprogram) is programmed by a numerical integral method, and it is verified by the existed test. It is concluded that the theoretical values of the lateral displacement are consistent with the test values of the lateral displacement, and the method is reliable and can be safely used for the analysis of RC column with special-shaped section. Furthermore, the calculating flexural stiffness reduction factor program is also compiled by a numerical integral method.Based on the M -Φprogram and P -Δprogram, equal RC columns with T-shaped section are analyzed under loading angle of 90°and 270°, and RC column with equal十-shaped section is analyzed under loading angle of 0°( 90°, 180°, 270°) and 45°(135°, 225°, 315°), and RC column with unequal十-shaped section is analyzed under loading angle of 0°( 180°), and 90°( 270°). The influence regularity of concrete strength, axial load level, reinforcement ratio, slenderness ratio, limb thickness, hoop spacing, and concrete cover thickness on flexural stiffness reduction factors are analyzed. It is concluded that the loading angles have influence on the flexural stiffness reduction factors, the flexural stiffness reduction factors increase as the concrete strength and reinforcement ratio improve, the flexural stiffness reduction factors decrease as the axial load level and slenderness ratio improve, and the limb thickness, hoop spacing and concrete cover thickness have a little influence on flexural stiffness reduction factors.As a result, flexural stiffness reduction factors are proposed to consider characteristics of material nonlinearity and geometrical nonlinearity of RC column with special-shaped section.