Modeling masonry-infilled RC frames. A critical evaluation of NTC08 provisions

RC frames are often infilled with masonry. The masonry panels, for stiffness and strength, can modify the behavior of infilled frames and thus their modeling. NTC08, relatively, reads: "In the model definition, non-structural elements (such as infilled panels and partitions) can be represented only in terms of mass; their contribution to the structural system behavior in terms of stiffness and strength will be considered only if it has negative effects for safety purposes." The indication, generally cautionary, “let neglect stiffness and strength” is both uneconomical both shortsighted; one in fact renounces to evaluate the masonry infilled frames behavior and, more precisely, to design the masonry infills and thus to exploit usefully their features that, if properly defined, can produce significant economies. This article, after comparing critically the ways in which the masonry infill panels are modeled, suggests which model should be chosen and the correctives to adopt for it; highlights then, through a parametric analysis, the changes that masonry infill panels induce in the behavior of RC frames and how such changes may be usefully exploited for design purposes. Finally it suggests, through the results obtained, how to change NTC08 prescription.