AN APPROXIMATE ANALYTIC SOLUTION FOR DISTORTION OF THIN-WALLED ORTHOTROPIC BEAMS WITH SYMMETRIC CROSS-SECTIONS SUBJECTED TO TORSION

The cross-section distortion of thin-walled beams of open sections assembled of three plates subjected to torsion is considered. The transverse loads act in beam wall planes. The cross-sections with two axes of symmetry are considered. The isotropic as well as orthotropic materials with equal or approximately equal modulus of elasticity in both directions are considered. It is assumed that the stresses and displacements due to cross-section distortion have small influence on the stresses and displacements according to the classical theories of torsion of thin walled beams, where the cross sections maintain their shape, and may be ignored. It is assumed that the stresses and displacements due to cross-section distortion are proportional to the additional angle of torsion due to shear according to the theory of torsion of thin-walled beams of open section with influence of shear. The results are compared to the results of the finite element method using shell finite elements.