Many gravity load designed reinforced concrete frames are nowadays located in seismic areas. Their design carried out without seismic provisions generally results in an unsatisfactory response during earthquake events. The main issues related to the behavior of such structures are outlined in Chapter 1. Then, Chapter 2 discusses strengthening strategies suggested by the main seismic guidelines; different upgrade methodologies are also summarized distinguishing those based on traditional and composite materials, respectively. A brief summary of tests on interior connections is proposed with particular attention to used test setup.

Chapters 3 and 4 deal with the proposed upgrade technique based on the use of composites. The innovative aspect of combining FRP bars and laminates is underlined and developed tests are detailed. The technique is based on using near surface mounted (NSM) FRP rods providing flexural strengthening and lay-up laminates improving the confinement of columns and the strength of the joint. Test results are discussed in Chapter 5 and the influence of the FRP strengthening on strength and/or ductility is assessed. Overall, experimental results showed that such technique could become a promising and sound methodology for the upgrade of RC connections, provided that constructability issues are also addressed. Along with the discussion on global performance, the analysis of stresses in the joint is carried out in order to define failure criteria for the design of the connection upgrade.