THE RESPONSE OF STRONGBACK SYSTEM WITH DIFFERENT VISOCUS DAMPERS PLACEMENTS

In the present paper the seismic behavior of structural systems obtained by connecting a moment resisting frame structure with a vertical elastic truss, known in the literature as strongback, which acts as a mast by imposing to the structure a given lateral deformed shape, is investigated when coupled with viscous dampers. The presence of the strongback, which has to be designed in order to remain in the elastic field under strong seismic ground motion, linearizes the lateral displacement profile of the adjacent frame through an exchange of mutual horizontal actions. The presence of the strongback should thus help in limiting undesired effects such as soft-storey and weak-storey mechanisms since a uniform distribution of inter-storey drifts along the height of the frame structure is achieved. A frame structure equipped with dissipative devices and characterized by a known (e.g. linear) lateral deformed shape can be, at first approximation, reduced to an Equivalent Single Degree Of Freedom (ESDOF) system, characterized by an equivalent lateral stiffness, mass and damping coefficient. This simplification allows therefore to obtain an analytical relationship between the damping coefficient of each single device and the damping ratio of the entire system that can be used to size the damping system in the preliminary design phase. The work presents the results of numerical simulations to verify the effectiveness of the ESDOF procedure for different dampers configurations. In detail, inter-storey (IS) dampers placement is studied, either considering a uniform distribution of dampers at all inter-stories along the height of the frame or dampers allocated at one or few inter-storey.