Elemento de Viga Baseado em Formulação de Rigidez Enriquecido com Funções de Forma Adaptativas para Garantir Equilíbrio Axial

In the framework of Performance Based Earthquake Engineering (PBEE), assessing the inelastic behaviour of structures both at the global (force-displacement) and local (stress-strain) level is of priority importance. This goal is typically achieved by advanced nonlinear analysis that rely on the use of increasing computational power. Due to a good compromise between accuracy and processing time, distributed plasticity beam elements represent the most employed finite element in nonlinear structural analysis. In particular, displacement-based elements are the simplest in terms of implementation and the most efficient from the state determination viewpoint. However, a fundamental drawback of classical displacement-based formulations is related to the assigned axial displacement field. This limitation implies that equilibrium is only verified on an average sense and, in case of material nonlinearity, it yields different values of the axial force in distinct integration sections. This results in a misevaluation of the moment capacity of the structural member and therefore in a poor local and global performance of the finite element. In this paper a new displacement-based element strictly verifying the axial equilibrium condition is introduced. The latter was implemented by the authors in an ad hoc finite element software and its performance is presented by means of two application examples. Comparisons between classical displacement-based and force-based formulations are made, both at the global and local level.