**7. Conclusion**

In this chapter, bending collapse of rectangular tubes was investigated using the FEM numerical simulation. The Kecman's method in which the post buckling strength of the flange and the effect of the flange slenderness on the cross-sectional fully plastic yielding are taken into account is effective when the aspect ratio of web to flange is not large. However, in order to predict accurately the maximum moments of rectangular tubes with large aspect ratio of web to flange, the slenderness of web has to be taken into account. Our new method in which the post buckling strength of the web under stress gradients and the effect of the web slenderness on the cross-sectional fully plastic yielding are taken into account are proposed, and the predicted maximum moment agrees with the results of FEM numerical simulations.

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