A model for the practical nonlinear analysis of reinforced-concrete frames including joint flexibility

A model is developed to simulate the nonlinear response of planar reinforced-concrete frames including all sources of flexibility. Conventional modeling approaches consider only beam and column flexibility using concentrated plasticity or springs to model this response. Although the joint may contribute the majority of the deformation, its deformability is typically not included in practice. In part, this is because few reliable, practical approaches for modeling all sources of frame nonlinearity are available. The research presented herein was undertaken to develop a practical, accurate nonlinear model for reinforced concrete frames. The model is appropriate for predicting the earthquake response of planar frames for which the nonlinearity is controlled by yielding of beams and/or non-ductile response of joints and is compatible with the ASCE/SEI Standard 41-06 nonlinear static procedure. The model was developed to facilitate implementation in commercial software packages commonly used for this type of nonlinear analysis. The nonlinearity is simulated by introducing a dual-hinge lumped-plasticity beam element to model the beams framing into the joint. The dual-hinge comprises two rotational springs in series; one spring simulates beam flexural response and one spring simulates joint response. Hinge parameters were determined using data from 45 planar frame sub-assemblage tests. Application of the model to simulate the response of these sub-assemblages shows that the model provides accurate simulation of stiffness, strength, drift capacity and response mechanism for frames with a wide range of design parameters.

► Practical pushover model for RC frames that account for joint flexibility. ► Lumped-plasticity beam elements modified to account for nonlinear joint response. ► Brittle joints: Accurate simulation of stiffness and strength. ► Ductile joints: Accurate stiffness, strength, and drift at strength loss.