This work presents the theoretical aspects of a one dimensional computational approach for the determination of the cross sectional stiffness of composite rotor blades. The method is based on a vector variant of the classical lamination theory embedded into a geometrically exact large deformation-small strain thin-walled beam formulation, which is naturally oriented to multibody problems. The procedures rely on a one-dimensional discretization of the aerodynamic profile of the blade; this generates groups of finite segments of composite laminates which are assembled to find the stiffness properties of the blade cross section. The formulation accounts for warping and transverse shear; the warping problem is solved numerically by means of a one dimensional finite element formulation. The numerical tests show that the formulation gives very accurate results. (C) 2015 Elsevier Ltd. All rights reserved.