Finite element modeling of open-section composite beams with warping restraint effects

A new finite element model is developed to capture spanwise torsion-related warping restraint effects in open-section composite beams, The new model features both twist and twist rate degrees of freedom, allowing for direct implementation of the kinematic boundary conditions associated with torsion-related warping restraints, A Vlasov cross-sectional model is used to determine the beam stiffness coefficients, The new model is validated against closed-form solutions for uniform composite I beams and detailed shell element solutions for more general spanwise geometries and loading conditions, A previous method of modeling spanwise torsion-related warping effects is reviewed and compared to the current model. Beams with spanwise taper, elastic couplings, and arbitrary warping boundary conditions are analyzed. Bending loads and distributed torsional loads are also investigated. Excellent correlation is observed between the current model, closed-form solutions, and finite element solutions, For beams with uniform cross-sectional and warping restraints at both ends, the global increase in torsional stiffness due to torsion-related warping effects is independent of distributed loadings. The stiffness increase was found to depend on the cross-sectional geometry in the vicinity of the restraint. For extremely slender beams, the new torsion model yields the classic St. Venant torsion solution.