The Influence of Bearing Stiffeners to Double - Symmetrical I - Section’s Torsion Stiffness, an Analytical Approach

Abstract

Bearing Stiffeners are preventing web-local-buckling and reinforcing this section for point-loads and shear-forces. This paper discusses bearing stiffeners’ contribution in enhancing double-symmetric I-sections’ torsion capacity. Based on the Saint Venant’s formula torsion stresses are carried solemnly by the section, neglecting the stiffeners’ contribution. However, these stiffeners exhibit significant rotational deformation with the I-section in warping, indicating development of internal forces, restraining the warping. Therefore, the negligence of stiffeners’ contribution in Saint Venant’s torsion formula has to be revised. Torsions within the stiffeners are the Saint Venant’s and torsion-shear-stresses induced by bending. Assuming out-of-plane stresses neglected, normal and bending-shear torsion stresses are zero, leaving only the Saint Venant’s. From equilibrium at the stiffener –to-flange’s-joint, the stiffeners’ natural boundary conditions equation can be obtained. Their presence leads to a rotational-torsion function differentiation along the beam, between stiffeners. But since all points have identical internal torsion forces, the disturbed differential torsion warping equations are identical. Using the geometrical and natural boundary conditions equation the mathematical-rotational-torsion-solution for each field along the beam is obtained. It can be concluded that the member’s torsion stiffness increases approaching to linear while the increment will approach a hyperbola as a function of stiffeners’ number and thickness, respectively.