Influence of infill panels and their distribution on seismic behavior of existing reinforced concrete buildings

Infills can highly influence the seismic response of a Reinforced Concrete (RC) building: generally speaking, their presence leads to an increase in global stiffness and strength, but their brittle behavior can result in an increase of displacement demand if a certain threshold of seismic intensity is overcome. Moreover, presence of infills often leads to a change in the collapse mechanism compared with the bare structure, leading, for instance, to column-sway storey mechanisms characterized by a detrimental localization of inelastic displacement demand. In this paper, a numerical investigation of the influence of infills on the seismic behavior of a case-study existing gravity load designed RC building is carried out. Different infill configurations are considered (Bare, Uniformly infilled and Soft-storey infilled). Seismic capacity assessment is carried out by means of Static Push-Over analyses, within the N2 spectral assessment framework. A sensitivity analysis is carried out, thus evaluating the influence of main material and model parameters on seismic response at different Limit States, namely Damage Limitation and Near Collapse, mainly due to the change in parameters as effective period of vibration, base shear and displacement capacity.