In this work, the first-order behavior of naturally curved thin-walled bars with circular axis, without pre-twist, is assessed with the help of the Generalized Beam Theory (GBT) formulation previously developed by the authors. With respect to the previous work, which dealt with simple cross-sections, the present paper presents a method to obtain the deformation modes for arbitrary flat-walled cross-sections. Despite the complexity involved in this generalization, the standard GBT kinematic assumptions are kept, since they are essential to (i) subdivide the modes in a meaningful way and (ii) reduce the number of DOFs necessary to obtain accurate solutions. It is shown that the curvature of the bar influences significantly the deformation mode shapes. Furthermore, a standard displacement-based finite element (FE) is employed to solve several examples that highlight the peculiar behavior of curved members. For validation and comparison purposes, results obtained using shell FE models are provided. Finally, the superiority of a mixed GBT-based FE format is demonstrated
