A modeling approach for plane frames with deformable beam-column joints

A simple but effective modelling approach for reinforced concrete (R/C) plane frames is here proposed, to account for the deformability of beam-column joints. In this procedure, kinematic assumptions, previously derived for the behaviour of a steel joint, establish a relation among the twelve lagrangian coordinates of beams and columns framing into the joint and the eight coordinates - encompassing three rigid body and five deformation modes - of the joint element. The second set of coordinates is compatible with an isoparametric 4-node finite element, where longitudinal and transverse reinforcements can be introduced as embedded bar elements. In this way, the usual modelling of plane frames is retained, at the expenses of an increase in the number of degrees of freedom associated to the node. The effect of the adoption of the proposed model on the lateral deformability of structures at the serviceability limit state is evaluated by comparison with other modelling approaches widely used. In the linear range, the model is validated against a few experimental data in the literature.