Strongback system to enhance the building seismic response of framed structures

In the present paper the behavior of a special structural system is investigated: the innovative system is composed of a vertical elastic truss, known in the literature as strongback, which acts as a mast when coupled with frame structures by imposing to the latter one a given lateral deformed shape. The rigid behavior of the strongback, designed to remain in the elastic field under strong seismic ground motion, imposes a uniform inter-storey drift along the frame height, thus avoiding undesired effects such as soft-storey and weak-storey mechanisms. Therefore, the combined structural systems can be modelled at first approximation as an equivalent Single Degree of Freedom system, thus allowing for a simple analytical description of its response. In particular, in the present work the attention is mainly focused on the mutual actions exchanged by the strongback and the frame, through infinitely rigid connections at each floor. Assuming a shear-type behavior of the frame, an analytical solution of the static equilibrium equations is found. Finally, some numerical simulations of the seismic response of the frame systems with strongback systems are developed, both considering shear-type frames and frames with flexible beams.