角形CFT断面の累加強度と終局強度の比較

<p> 1. Introduction</p><p> The objective of this study is to present the expressions for calculating the ultimate flexural strength and to examine the relations between the superposed strength and the ultimate strength of rectangular concrete filled tubular sections. In addition to the superposed strength, a method to calculate the ultimate flexural strength is presented. Numerical calculation based on the theoretical analysis is performed taking the width-to-thickness ratio of steel tube, strengths of steel and concrete and the ultimate strain as the analytical parameters, and moment -axial load interaction relationships are shown. Comparing the ultimate strength with superposed strength, the effects of analytical parameters on the strengths are discussed.</p><p> </p><p> 2. Analytical work</p><p> The expressions to calculate the generalized superposed strength of the rectangular CFT sections shown in Fig. 1 are given as the Eqs. (8) ~ (12), together with the expressions for the simple superposed strength of Eqs. (14)~(18). In addition to the superposed strength, the expressions for calculating the ultimate strengths are shown as the Eqs. (28) ~ (32) and (34) ~ (37).</p><p> </p><p> 3. Results and discussions</p><p> As the analytical parameters, the width-to-thickness ratio, yield stress of steel tube, compressive strength of concrete and ultimate strain of concrete are selected, and they vary as follows; 1) width-to-thickness ratio 20 and 40, 2) yield stress of steel tube 325, 440 and 700N/mm², 3) compressive strength of concrete 30, 60 and 90 N/mm² and 4) ultimate strain of concrete 0.004 and 0.008.</p><p> Relationship between the non-dimensional moment and axial load are shown in Figs. 11 and 12. In these figures, group "CFT", "S" and "C" denote the strength of CFT sections, steel tubular sections and concrete sections, respectively. It is shown that the effect of the ultimate strain on CFT strength becomes large as the strengths of steel and concrete become large. Figure 13 show the relationships the ratio of simple superposed strength _S+CM_pc to generalized superposed strength _cftM_pc and the axial load ratio. It is observed that the ratio _S+CM_pc/_cftM_pc becomes large as the effect on strength by the concrete becomes small. Figures 14 and 15 show the M_u/_cftM_pc ratio, where M_u denotes ultimate flexural strength. In the case of ultimate strain is equal to 0.004, the minimum ratio M_u/_cftM_pc is about 0.7, whereas the ratio is about 0.9 when the strain is 0.008.</p><p> </p><p> 4. Conclusions</p><p> The conclusions derived from this study are as follows:</p><p> 1) The expressions for calculating the ultimate strengths are presented as the Eqs. (28) ~ (32) and (34) ~ (37).</p><p> 2) The ratio _S+CM_pc/_cftM_pc becomes large as the effect on the strength by the concrete becomes small.</p><p> 3) In the case of the ultimate strain is equal to 0.004, the minimum ratio M_u/_cftM_pc is about 0.7, whereas the ratio is about 0.9 when the strain is 0.008.</p>