A Low-Damage Retrofitting Solution Based on Carbon-Wrapped Steel Tubes for Beam-Column Friction Connections of Existing Precast RC Structures

The 2012 Emilia earthquakes caused significant damages to existing precast RC structures. These buildings were found being extremely vulnerable because, being designed for vertical loads only, they featured friction-based connections between structural elements, and in particular between beams and columns. Given the large diffusion of these structures as industrial buildings, and consequently the high social and economic impact of damages, their retrofit is critical. Various techniques have been proposed in the literature; in most of them friction-based connections are removed by inserting mechanical connectors that will make beam-column connections hinged. These approaches lead to a significant increase of the base shear and therefore often require strengthening of columns and foundations. The research presents dissipative devices based on carbon-wrapped steel tubes to be used as an alternative low-damage solution for the retrofit of beam-column friction connections able to minimize structural damages. Firstly, the study presents results of experimental tests on the devices and discusses their innovative energy absorption mechanism and dissipative behaviour. Then, numerical analyses carried on to investigate the effectiveness of the introduction of dissipative devices in beam-column connections of precast structures are presented. Incremental Dynamic Analyses have been performed in order to evaluate an equivalent behaviour factor for structures with dissipative devices, by comparing the seismic response of simple frame structures with dissipative connections with equivalent elastic systems. Findings of numerical investigation show how the introduction of the dissipative devices in friction-based joints provides an effective connection between structural elements and, in addition, the capability to reduce forces transmitted to the columns, improving the seismic behaviour of the entire structure. Finally, a simplified approach to evaluate an equivalent behaviour factor for a structure equipped with dissipative devices in friction-based beam-column joints is proposed.