Corner Beam-Column Joints Seismic Retrofitting With High Performance Fiber-Reinforced Concrete Jacketing C. Beschi & P. Riva Department of Design and Technologies, University of Bergamo v.le Marconi 5, 24044 Dalmine (BG), Italy. E-mail: paolo.riva@unibg.it A.Meda Civil Engineering Department, University of Rome “Tor Vergata”, via del Politecnico 1, 00133 Rome, Italy. E-mail: alberto.meda@uniroma2.it SUMMARY: The experimental results on full-scale corner beam-column joints tests are presented herein, with the aim of studying the effectiveness in strengthening existing RC existing structures of the application of a HPFRC jacket. The specimens subassemblies have been designed with structural deficiencies typical of the Italian construction practice of the 60’s-70’s: absence of any capacity design principle, use of smooth bars, inadequate reinforcement detailing, such as total lack of stirrups in the joint panel and hook-ended anchorage. Both unretrofitted and retrofitted specimens have been tested under simulated seismic loads. The results underline the significant vulnerability of the joint panel region and the critical role of the slippage phenomena related to the use of smooth bars and show that, with the application of a HPFRC jacket, it is possible to increase the bearing capacity of the columns, reaching also an adequate level of ductility and strength of the beam column joints. Keywords: existing RC structures, seismic retrofitting, HPFRC jacketing, beam-column joint. 1. INTRODUCTION The Abruzzo earthquake (6th April 2009) dramatically demonstrated that a large amount of the Italian existing RC structures, designed only for gravity loads, was not able to sustain the earthquake actions, mainly due to structural deficiencies related to scarce material properties, usually low-strength concrete; absence of capacity design principles; inadequate confinement in the potential plastic regions, typically no transverse reinforcement in the joint regions; poor reinforcement detailing, such as insufficient amount of column longitudinal reinforcement, inadequate anchorage detailing, lapped splices of column reinforcement just above the floor level, use of smooth bars for both longitudinal and transverse reinforcement. From the observation of the effects of past earthquakes, it is widely recognized that beam-column joints represent a critical region in frame buildings subjected to seismic loads of high intensity. At the global level, a weak-column/strong-beam system results, with the risk to develop soft-storey mechanisms. At the local level, inadequate protection of the panel zone region within beam-column joint subassemblies is expected as well as brittle failure mechanisms of structural elements. The strengthening of existing RC structures and the evaluation of the seismic response of existing RC buildings designed before the introduction of adequate seismic code provisions have thus become an urgent issue in Italy. During the last decades, several techniques have been proposed for the seismic retrofitting of RC elements (Fib Bullettin 24 2003, Fib Bullettin 35, 2006, Fib Report 1991). Concerning the strengthening of existing columns, the possibility of using RC jackets is usually considered, in particular when the elements are made of low strength concrete. Traditional jacketing presents some inconvenience, due to the jacket thickness being governed by the steel cover, which often leads to a jacket thickness higher than 70-100 mm, with a consequent increase of both mass and stiffness,