SEISMIC RETROFIT OF EXISTING PRECAST RC BUILDINGS WITH DISSIPATIVE DEVICES BASED ON CARBON WRAPPED STEEL TUBES

The seismic vulnerability of existing precast RC buildings not designed against seismic actions is a well-known issue nowadays, as emerged from the aftermath of the seismic events that affected many productive areas in the Emilia region (north Italy) in 2012. This is a consequence of the lack of structural redundancy and the widespread adoption of friction-based connections, which can lead to collapses and significant damage to contents. Thus, the necessity of identifying suitable intervention strategies has been widely recognized by researchers, which proposed different retrofit techniques. One of the most diffused approaches is to introduce mechanical connectors between columns and roof elements, resulting in an increase of the base shear and the need to strengthen the columns. To prevent this phenomenon, dissipative devices based on Carbon-Wrapped Steel Tubes (CWST) are introduced herein for the retrofit of existing precast RC structures, aiming at reducing the forces transmitted to columns, and providing a suitable connection between columns and beams. To this regard, this paper discusses the seismic retrofit of an existing precast building equipped with CWSTs. Linear and non-linear time history analyses have been conducted on two different models of the structure, one with hinged beam-column connections, and on the one with CWSTs. The yielding and the ultimate rotations of the plastic hinges at the base of the columns as well as the cyclic shear resistance depending on the ductility demand on each element, are defined according to Eurocode 8 prescriptions. The paper discusses the effects of the introduction of the CWSTs in the connections in terms of forces and proposes equivalent behavior factor values for the two structures.