Simplified macro-modelling strategies for the seismic assessment of non-ductile infilled frames: a critical appraisal

Reinforced concrete frames (RCFs) represent the most widespread structural typology in several high-seismic regions worldwide. Two categories of buildings can be distinguished: modern buildings designed following a specific seismic code and existing buildings designed only to resist to gravity loads. In both cases, the structural response of RCF may be positively or negatively conditioned by the non-structural masonry infills. Neglecting the infills in the analyses can produce an unsafe prediction of the seismic performance of a structure. In contrast, simplified modelling approaches are needed in current engineering practice, since rigorous modelling strategies, namely non-linear finite-element models, are generally incompatible with the standard hardware/software adopted by practitioners. In this paper two macro-modelling approaches, namely the equivalent diagonal strut model and a recently introduced 2D discrete macro-model, which are currently employed by engineers for predicting the seismic behaviour of infilled frames, are compared. The aim of this investigation is to highlight the influence of the modelling approach and calibration procedures on the seismic performance assessment of infilled frame structures. A recent experimental study on a 1-bay infill frame prototype and a multi-storey frame are considered as benchmark cases. The results obtained highlight the differences between the two approaches in terms of capacity curves and collapse mechanisms.