On the role of equivalent strut models in the seismic assessment of infilled RC buildings

The participation of masonry infill panel to the overall seismic resistance of a framed building has a significant variation according to the specific mechanical characteristics of the infill, the geometrical distribution within the building and the local interaction among the panel and the surrounding primary RC elements. Especially in the case of structure designed only for vertical loads, essence of the infill can be decisive under an unexpected earthquake, providing an additional contribution to the strength and to the stiffness. On the other side, this beneficial role is often accompanied by the modification of the global collapse mechanisms, with the appearance of brittle failure modes. In the present paper, an existing RC framed building for which a good level of knowledge was available, including a wide experimental database, was chosen as a case study. A reference frame was considered for performing nonlinear static analyses aimed at investigating some significant aspects about the modelling of the infill and the relapse induced by the related computational choices on the structural response. In particular, it is faced the sensitivity analysis about specific parameters involved in the definition of the equivalent strut models: the width bW of the strut; the constitutive Force–Displacement law of the panel; the number of struts adopted to simulate the panel.