The present work proposes two different models to estimate, with adequate approximation, the stiffening contribution of an infill panel for low stress levels (elastic phase). The need for such models arose from a comparison previously carried out by some authors between the fundamental period values calculated with the formulation of the NTC 2008 and those obtained experimentally through a dynamic identification campaign on ambient noise conducted with reinforced concrete framed structures. After defining the problem, the study proceeds with the description of the various phases of the infill panel behaviour for various levels of action in the plane and then discusses the major numerical modelling techniques of the infill panel currently available. Based on considerations deduced from the analysis of various bibliographic contributions, the proposed calculation models are tested against experimental results obtained from various studies.
