抄録
Flexural deformation behavior of concrete filled steel tube beam-columns is discussed in elasto-plastic range. As the fundamentals of deformation analysis, the bending moment-curvature relationships of concrete filled steel tube beam-columns are derived analytically such as (12), (14), (16), (20) and (23) under the assumptions of the simplified mechanical properties of materials, i. e. perfectly elastic-plastic for concrete and bi-linear elastic-plastic with a gradient of μ_<stb.> E_s in plastic range for steel such as shown in Figs. 1 and 2. In these analytical expressions, it is indicated that the product of the strength ratios between concrete and steel β_s(=σ_y/F_c) and the thickness ratios of steel tube t_1(=t/r) is the main parameter. The influences of axial load level ratios N/N_y and the values of gradient μ_<stb.> upon the m-φ relationships are shown in Fig. 4 for a case of β_s・t_1=1.00. The load-deflection relationships are calculated on the bases of these moment-curvature relationships and the influences of axial load level ratios and bilinear plastic gradients upon them are shown in Fig. 6 for a case of β_s・t_1=1.00, too. Tests are carried out by a loading system such as shown in Fig. 5 on the specimens with a diameter of 139.8mm and a wall thickness of 4.5mm steel tube with a yield stress of 3800kg/cm^2 and concrete of a mean cylinder strength of 300kg/cm^2. The load-deflection relationships under various axial load level ratios of 2/3, 1/2, 1/3 and 1/6 are shown in Fig. 7 with solid lines and compared with computed values shown by dotted lines. Fig. 8 shows the tested values under constant axialload level ratio of 1/3 by solid lines and computed values are indicated by dotted lines for μ_<stb.>=0, 0.01, 0.02. The coincidence between tested (solid) and computed (dotted) values in Figs. 7 and 8 is very well, therefore, the analysis proposed here is reasonable enough.
