Adaptive force-based frame element for regularized softening response

The current paper presents a new proposal to obtain regularized responses with distributed plasticity force-based frame elements under strain-softening response. It is based on an automatic, computationally efficient, commutation between integrations schemes, which ensures simultaneously a high degree of accuracy for hardening behavior and an objective response during the post-peak phase(s). Additionally, the varying values of the sectional forces can be directly accounted for in the estimation of the applicable characteristic length. Finally, a number of numerical examples illustrate the regularized performance of the element.