A 3 ELEMENT MODEL FOR THE DAMAGE CONTROLLED DESIGN: THE CASE STUDY OF THE FAZZINI COLLEGE

Passive protection systems have proven to be efficient solutions for the seismic protection of both new and existing buildings. Recently an increasing attention is paid towards their use in external configurations, especially for existing structures due to their low interference with the structure and the activities within the buildings leading to a notable reduction of building downtime and impacts on users. This paper concerns a dissipative external system made of steel braced structures connected to an existing r.c. frame building, that is the Fazzini college of the University of Camerino severely damaged during the 2016 Central Italy seismic sequence. A the design method of the external passive system equipped with fluid viscous dampers has been proposed in this paper, aimed at preventing damage to both structural and non-structural components up to severe earthquakes. To achieve this target the design has been conducted by means of a three-element model representative of the structural system consisting of the existing building, the external structure, and the fluid viscous dampers. The dynamic response of such linear simplified model is governed by few parameters: (i) the mass and the stiffness of the building (ii) the stiffness of the external structure, and (iii) the damping contribution provided by the fluid viscous dampers. The efficiency of the system is strongly influenced by the ratio of the stiffness between the external structure and the building, which also influences the maximum amount of added damping exploitable. A parametric analysis has been carried out to evaluate the stiffness ratio that maximizes the efficiency of fluid viscous dampers, by monitoring a set of demand parameters like the forces and strokes of dampers, the inter-storey drift ratios and the floor absolute accelerations. Moreover, a such intervention, when applied to existing r.c. frame building designed without proper seismic details, should not disregard the important role played by infills and partition walls, that can notably affect the dynamic behaviour of the building due to their stiffness contribution. The proposed design methodology has been applied to the seismic retrofit of the Fazzini with the result that to enhance the efficiency of the retrofit all the infill walls and the partitions, both internal and external, should be replaced with drywall deformable elements.