Generalized Finite Element Formulation of Fiber Beam Elements for Distributed Plasticity in Multiple Regions

A generalized fiber beam element formulation is proposed to accurately capture the formation of multiple plastic regions with a coarse mesh, which usually occurs in the process of structural collapses. The strong gradient of displacement near plastic regions in a fiber beam element can be accurately described using a special plastic enrichment function. The two types of the plastic enrichment functions are suggested for the cases where the plastic region is located fully inside an element and spread over a node, respectively. In this approach, the optimal shape of the plastic enrichment function can be updated by reflecting plastic deformation at the previous loading step. Furthermore, if plastic regions appear in multiple locations in an element, the corresponding plastic enrichment function can be adaptively reconstructed on the basis of plastic region distribution without introducing additional degrees of freedom. The effectiveness of the proposed method is investigated in terms of accuracy and computational cost through several numerical experiments.