Theoretical considerations of post-buckling analyses of unsymmetric thin-walled space frames

The theoretical considerations of the post-buckling analyses of thin-walled space frames with non-symmetric cross sections are presented based on the semitangential rotation and semitangential moment. The nature of the Rodriguez's rotations and semitangential rotations are discusssed, and the improved displacement field is introduced based on the second order terms of semitangential rotations. By defining all the displacement parameters at the centroid and introducing the normalized warping functions defined at the centroid and the shear center, respectively, the elastic strain energy including bending-torsion coupled terms due to the non-symmetry of cross-section is clearly derived. Also, the total potential energy consistently derived, without unreasonable assumption, based on semitangential rotations corresponds to semitangential bending and torsional moments. It is proved that the conventional potential energy due to stress resultants corresponds to the quasitangential internal bending and torsional moments, and the potential energy considering the effects of the second order terms of semitangential rotations includes the energy terms transforming quasitangential moments to semitangential moments.