Seismic modelling of a strategic building: influence of infill walls

When analysing an existing structure, the accurate prediction of its natural frequencies is of utmost importance for the estimation of shear forces exerted at the ground level, and hence internal forces/moments acting within the structural elements. This aspect is relevant especially for tall buildings, whose fundamental period is higher than Tc* and an underestimation of the base shear force can be obtained if the stiffness is not properly accounted. For this reason, the influence of infill walls on the global stiff-ness should be considered. In the paper, a 14-storey reinforced concrete strategic building, 50 m tall, built in the sixties and located in Northern Italy is investigated. Dynamic tests were conducted to ascertain the free vibration frequencies of the structure and its mode shapes. The influence of infill walls is evaluated through a finite element model developed with a commercial software; once validated, the model will be used to perform pushover analysis that accounts for material non-linearity