Distortion of thin-walled beams of open section assembled of three plates

The cross-section distortion of thin-walled beams of open section assembled of three plates with two axis of symmetry is considered analytically. The consideration is based on the assumption that stresses and displacements due to the cross-section distortion have small influence on stresses and displacements according to the classical theories of thin-walled beams of open sections, where the cross-section contour maintains its shape, and may be ignored. It is assumed that stresses and displacements due to the cross-section distortion are proportional to the angle of torsion due to shear, according to the theory of torsion of thin-walled beams of open cross-sections with influence of shear. The results are compared with the finite element method, by using shell elements. Several examples are examined by both methods.