The influence of the web-flange junction stiffness on the mechanical behaviour of thin-walled pultruded beams

Composite thin walled members, produced by the manufacturing process of pultrusion, exhibit structural behaviour that is governed by their specific stiffness and strength properties.Although the basic knowledge about their constitutive behaviour has already been assessed in current technical literature, several relevant features are still being studied. They include the evaluation of the long term behaviour, the influence of the shear deformations, the buckling load as well as the influence of the web-flange junction stiffness.Due to the presence of unidirectional fibres along the length of the beam, the condition of a rigid connection between the flanges and web panel should be replaced by accounting for possible relative torsional rotations, which can influence the pre-buckling behaviour.In this paper, a one dimensional mechanical model with the purpose of detecting such an influence is presented. The model, which is based on many common assumptions (a linear kinematics conjugated with small strains and moderate rotations), is innovative in relation to the presence of a few additional degrees of freedom which allow to simulate the web/flange relative rotations, thus generalizing the classical assumptions concerning the generic cross-section which maintains it un-deformed.Many numerical examples obtained by using a finite element approximation with the aim of highlighting the model capabilities have been developed.