A linear theory of beams with deformable cross section

T. we present a direct model of beam which takes into consideration the deformationof the section by effect of orthogonal actions. the variation of size and the distortion of thetransversal sections are taken into account as well as the usual rigid rotation-torsion-warping.we deduce the equations of motion in terms of the kinematic descriptors. a simple numericalexample is also presented to show the consistence of the proposed model.