On the fibre modelling of beams in RC framed buildings with rigid diaphragm

The development of an accurate numerical model plays a key role for the proper assessment of structures. To this end, fibre modelling is widely considered as one of the most rigorous tool for an accurate evaluation of the seismic response of RC framed buildings. However, it has been noted that the interaction between fibre modelled RC beams and the rigid diaphragm adopted to simulate the concrete slab, typical of RC buildings, may cause the development of unintended fictitious axial forces in beams. These axial forces may lead to an overestimation of the resisting bending moment of beams cross section, thus altering the distribution of yielding in the structural members and the collapse mechanism. The goal of this paper is to overcome this drawback by introducing at one end of each beam a simple additional element, named axial buffer element. This element allows the axial deformation of the beam, prevents the development of fictitious axial force and does not invalidate the transmission of shear force and bending moment. The paper investigates the influence of the presence/lack of the axial buffer element on the seismic response of a set of RC buildings representative of real structures. For this purpose, incremental nonlinear dynamic analysis and nonlinear static analysis were conducted.