A new mathematical model for three-dimensional thin-walled curved beam element of closed
section with seven degree-of-freedom per node is derived using the finite element procedure. The
seventh degree-of-freedom is to account for warning restraint effects in thin-walled closed sections.
These effects may become significant and should be fully considered in such sections for which
warping deformations are relatively large. This model considers the coupled action due to the
curved geometry of the element using its exact static behavior in the derivation of the displacement
field. Also, the modei considers the non-uniform torsional behavior of closed thin-walled sections
in cases where additional axial direct stresses and complementary shear stresses are formed. The
developed warping function of this model considers the interaction between the normal warping
stresses and the accompanying warping shear stresses as well as the coupled action between the
torsion and bending.In addition to the ordinary axial and flexural deformations, the strain energy, which is used to
obtain the stiffness matrix of the developed curved beam element fully, considers the additional
axial, primary and secondary shear deformations due to warping restraint. The validity of this
element is investigated by comparing the developed program analysis results with some available
analytical solutions.