The present work presents a subparametric finite element model with spline displacement functions, implemented for static, dynamic and instability analysis of folded plates, thin-walled beams, box girders, and elongated structures such as bridges and structural shapes. A drilling degree of freedom (rotation about an axis perpendicular to the plane of the element) is introduced in the formulation to allow for three-dimensional analysis. A method for determining the corresponding contribution to the stiffness matrix is presented. The examples presented evaluate the accuracy obtained using a small number of longitudinal subdivisions of the continuum, convenient in the case of analyses for preliminary design and optimization. The results obtained are compared to theoretical solutions or results of standard structural analysis programs, allowing for an appraisal of the advantages and limitations of modeling with use of spline functions. The differences in the results, observed specially in the case of thick plates, are explained by the approximations for the shear strain in the elements used for comparison. From the examples it is possible to comment results of threedimensional modeling of instability problems with different boundary conditions.