Torsion of open and closed thin-walled laminated composite sections

Vlasov's theory is expanded to perform the linear analysis of open and closed sections made of general laminated composites. Following the guidelines of Mechanics of Laminated Beams, the transverse shear deformations are included in the formulation. To overcome the overestimation of stiffness by the often assumption of negligible tangential stress, the laminate resultant force and moment are instead set to zero in this paper. The present model accounts for all possible elastic couplings in composite sections, such as extension- and bending-torsion. Applications of the formulation to flanged and box sections are presented and guidelines are provided on how to evaluate the torsional stiffness coefficients of the beam. A general solution for a fixed composite beam under tip torsional loads is derived, and the steps can be used to derive solutions for any other boundary conditions. The effect of warping-torsion on the torsional stiffness of the beam is investigated. Composite beams were tested in torsion and the angle of twist and shear strains were measured for verification of the analytical model predictions, which agree closely with the experimental results and finite element results.