Axially Equilibrated Displacement-based Beam Element: Implementation in OpenSees and Application to Dynamic Analysis of Structures

Experimental tests on the inelastic behavior of RC bridge piers have shown that, due to tension shift effects, the curvature profile above the base section of the structural member differs from the one that would develop according to a force-based or a classical displacement-based beam formulation with plane section hypothesis. Due to the inclined cracks in concrete members, it was found that the curvature distribution evolves in a bilinear shape along the member height during the inelastic phase of the response, and that the length of plastification increases with increasing ductility demands. Recently, it was shown that axially equilibrated displacement-based elements can more effectively predict the local-level response of RC members. The process of imposing the equilibrium of the axial forces along the element length allows the beam element to improve the simulation of both curvature and strain profiles. The finite element was originally implemented in the authors’ structural analysis software SAGRES, which was developed for nonlinear static analysis and is not freely available to the engineering community. This paper presents the validation of the implemented axially equilibrated displacement-based element in the open source finite element software OpenSees and provides some application examples of both nonlinear static and dynamic analyses. The results are compared against classical approaches (force-based and displacement-based), pinpointing the advantages of the axially equilibrated displacement-based beam element.