ENRICHED BEAM FINITE ELEMENT MODELS WITH TORSION AND SHEAR WARPING FOR DYNAMIC ANALYSIS OF FRAME STRUCTURES

his work investigates the performance of the enhanced beam Finite Element (FE) formulations proposed in [20] for the dynamic response of frame structures subjected to shear and torsional actions. These formulations introduce enriched kinematic descriptions to describe the out-of-plane deformations of beam cross-sections, in addition to the standard in-plane rigid modes. First model is based on the Vlasov’s theory, enriched to include shear induced warp- ing, and is developed according to a displacement-based approach. To this end, additional degrees of freedom (DOFs) are introduced at the two element end nodes and are used to inter- polate warping along the element axis, so that the influence of warping restraints at the element boundaries are properly accounted for. Second model is based on the Benscoter’s warping the- ory, also enriched to include shear warping, and is developed according to a mixed formulation free from shear-locking. Third model is the extension of second formulation and considers a general and accurate warping description. Indeed, a variable number of additional DOFs is introduced over the element cross-section and the warping displacement field is interpolated at two levels, along the beam axis and over the cross-section plane. Numerical analyses are presented to assess the performances of the three models in de- scribing the seismic response of frame structures, when shear/torsional actions dominate the structural behavior. Results are compared with the solutions obtained from standard beam and more involving shell and brick FE models.