TECNICHE INNOVATIVE PER IL MONITORAGGIO E IL RINFORZO DI STRUTTURE ESISTENTI Confinamento mediante compositi FRCM di strutture in cemento armato

For the last 100 years, concrete has been the most used material in constructions. However, reinforced concrete (RC) structures are subject to aging, environmental deterioration and possible damage due to excessive loading during their service life. In addition, poor detailing, lack of seismic design and evolution of standards and building codes urge for retrofitting interventions on these structures today. Innovative materials and techniques to monitor and strengthen existing structures have been the focus of research in recent years. Among these, rehabilitation of RC elements through the use of external jacketing technique has become a common practice in order to meet increasing performance requirements both for damaged or under-designed elements. Traditionally confinement was obtained through the installation of external steel plates bolted or welded together. The technique evolved to the use of external reinforced concrete and later to composite jackets. The latter includes mainly two materials: the more traditional and well-known FRPs (Fiber Reinforced Polymers) jackets and the more recent FRCM (Fiber Reinforced Cementitious Matrix) ones, also known as TRM (Textile Reinforced Mortar), obtained by replacing the organic matrix of the FRPs with an inorganic, generally cementitious, one. In the first part of this work, the state of the art was investigated analyzing existing literature for both FRP and FRCM confinement. Particular attention was paid to past experimental campaigns, existing analytical models, standard codes and guidelines, to evidence research gaps and inconsistent results. As a result, a comprehensive database was created for both FRP- and FRCM-confined specimens. Existing models for FRP and FRCM concrete confinement were analyzed to assess their ability to predict the axial behavior of confined elements. This stage of the work highlighted that FRP confinement models are more accurate than FRCM confinement ones, which, due to their more recent introduction, are generally based on a limited number of small-scale tested specimens. The predictive accuracy for both confinement systems varies significantly based on the cross-section geometry of confined elements and on the presence or not of internal transversal steel reinforcement (TSR). According to the above-mentioned research context, four experimental campaigns were carried out, aimed at investigating the behavior of FRCM-confined concrete, in terms of: i. Confinement effectiveness of RC columns through FRCM composites; ii. FRCM confinement as a repair technique for damaged RC columns through excessive axial loading; iii. Axial cyclic behavior of FRCM-confined concrete; iv. Behavior of FRCM-confined RC column under cyclic horizontal loading. The results of such experimental activity are summarized in the second part of this thesis. In the third part of this research work, the experimental results were used to develop an axial stress-strain design-based model for FRCM-confined concrete that meets the requirements of simplicity and ability to predict the axial behavior of confined concrete as accurately as possible. Finally, a framework on how to use and schedule FRCM confinement as a seismic retrofitting strategy for existing RC bridges, through time-variant seismic reliability profiles, is introduced.