Distributed and concentrated inelasticity beamcolumn elements: Application to reinforced concrete frames and verification

Abstract

Inelastic beam elements are widely used in the analysis of structures subjected to seismic actions. These elements are capable of describing the linear and nonlinear force-displacement and moment-rotation response of beams, columns and shear walls. However, there are numerical inaccuracies associated with these element formulations, as well as differences in computational effort. In this paper, the fundamentals of displacement-based and force-based elements are briefly presented, with emphasis on localization issues due to strain softening, and regularization procedures necessary to achieve convergence to single solutions. The modelling criteria regarding the number of integration points, the number of elements in each member and the length of the prescribed plastic hinges are also discussed. A one-story reinforced concrete frame, representing industrial buildings, has been modelled in a finite element software with the objective of studying the efficiency of three element types: displacement- and force-based distributed plasticity elements and concentrated plasticity ones. The running times of the analyses confirm that the computational demand of models with displacement-based elements is larger than that of models with force-based elements. Analysis results have then been compared to the experimental values obtained from a series of pseudo-dynamic tests performed with increasing seismic intensity. All element formulations showed very good approximation of the global response. Overall, force-based and plastic hinge models performed slightly better than the displacement-based model.