Parametric study on retrofit of rc framed buildings by dissipative tower

Italy is a country with high seismicity, but most of the existing buildings does not comply with current seismic standards. Indeed, they were designed before the enforcement of seismic standards or according to old seismic codes. A large number of these buildings is endowed with RC framed structure. These structures are inadequate in terms of lateral stiffness and strength to support seismic actions, cannot guarantee a ductile collapse mechanism, and thus result in safety risks to society. Therefore, these buildings need to be seismically retrofitted. In this paper, the addition of external dissipative towers (seismic-resistant steel towers equipped with Maxwell nonlinear fluid viscous dampers (FVDs)) to the existing RC building is proposed for retrofit. This technique is expected to reduce the seismic demand of the existing structure. The first goal of this study is to investigate and quantify the benefits gained by means of the dissipative towers for seismic retrofit of RC buildings. The second goal is to study, through parametric analysis, the influence of size and heightwise distribution of FVDs and of the stiffness of the steel tower, on the seismic response of the building to identify the combination of the features that lead to the best enhancement of seismic performance. To this end, a pilot building, representative of existing RC framed buildings, is designed and a numerical model of the building with and without damper-tower system is developed. Then, incremental nonlinear dynamic analyses are performed, and the results are used to determine the seismic performance in terms of fragility curves and mean annual frequency of exceedance of selected limit states. Comparing the results of systems with and without dissipative towers quantifies the achievable benefit, while the comparison of the results of systems retrofitted by different dissipative towers provides information on the influence of the design parameters.