Seismic retrofit of real beam-column joints using Fiber Reinforced Cement (FRC) composites

This study deals with the seismic behavior of old- type reinforced concrete (RC) beam-column joint and the effectiveness of an innovative application of Fiber Reinforced Concrete (FRC) as seismic strengthening solution. Two real joint subassemblies were extracted from an existing building damaged and demolished after the L’Aquila 2009 earthquake and tested in laboratory. The joints exhibited poor quality concrete and reinforcement details typical of old design practice, which are very difficult to reproduce in laboratory simulations. The joint tested in the as-built configuration showed a brittle failure with joint diagonal cracking, as commonly observed in the aftermath of recent devastating earthquakes. The FRC thin jacketing avoided the joint panel shear failure promoting a more favorable beam yielding. This resulted in a significant increase of the shear strength (until 50%) and energy dissipation (85%). The strengthening phases and the details of the proposed strengthening layout are described. A direct comparison between as-built and strengthened specimen in terms of global and local behavior is reported. Strain measurements on the FRC jacketing are also discussed as an effective design parameter.