Seismic strengthening of exterior RC beam-column joint: basalt vs. carbon FRCM systems

This study examines fabric-reinforced cementitious matrix (FRCM) systems, with carbon and basalt fibers, to strengthen seismically deficient, exterior reinforced concrete (RC) beam-column joints. The experimental program includes a control specimen, tested to complete failure to establish baseline performance, and two specimens subjected to an FRCM strengthening procedure, respectively one with carbon FRCM and one with basalt FRCM. Before FRCM application specimens were initially loaded up to 85% of their ultimate capacity to simulate realistic seismic damage conditions, and then tested to failure after the retrofitting intervention. All specimens were instrumented to capture the structural response throughout the loading history. Strength enhancement and energy dissipation capacity were analysed to evaluate the relative effectiveness of carbon and basalt FRCM compared to un-strengthened conditions. Results indicate that both carbon and basalt FRCM composites achieved a significant strength enhancement while providing also additional energy dissipation capability. Finally, both strengthening systems effectively modified the failure mechanism from brittle joint shear failure to a more favourable beam-joint failure mode.