Numerical Issues in Distributed Inelasticity Modeling of RC Frame Elements for Seismic Analysis

The sustained development of computational power continues to promote the use of distributed inelasticity fiber frame models. The current article presents a comprehensive application and discussion of state-of-the-art formulations for the nonlinear material response of reinforced concrete structures. The broad character of the study is imparted by the joint analysis of the effects of the type of formulation (displacement based versus force based), sectional constitutive behavior (hardening versus softening response), and numerical integration parameters (such as quadrature method, mesh definition, or number of integration points). Global and local responses are assessed, along with a critical review of existing regularization techniques. An experimentally tested cantilever is used to conduct the study and illustrate the previous features. The example shows that the convergence of displacement-based meshes under objective response can be much slower than what preceding studies indicate, unlike their force-based counterpart. Additionally, the physical interpretation of the local response under softening behavior supports the proposal of a novel regularization scheme for displacement-based elements, validated through comparison against experimental results.