PBO-FRCM and CFRP strengthened reinforced concrete columns: In fire and post-fire behavior

This paper experimentally investigates the thermal response and post-fire structural behavior of seven short circular reinforced concrete columns. The variables include the type of strengthening system applied polypara-phenylene-benzo-bisthiazole (PBO) fiber-reinforced polymer (FRP) and fabric-reinforced cementitious matrix (FRCM), exposures (unexposed or fire-exposed), and using a cementitious-based Spray-applied Fire Resistive Materials (SFRM) insulation. Four columns were subjected to an ASTM E119 fire without any sustained load during the fire, while the other three columns were unexposed and served as controls. Two months after the fire test, fire-exposed columns were tested under axial loading and compared with unexposed ones. The steel rebar temperature in the insulated FRCM column remained below 150 °C for three hours, while this temperature was over 700 °C for the insulated CFRP-wrapped column. The post-fire axial tests indicated that the fire-exposed, insulated PBO-FRCM wrapped column retained a residual axial capacity of 92 %, significantly higher than the 21–66 % range observed in the other three columns. Considering reduced material properties, ACI code-based predictions for axial capacity showed reasonable accuracy with predicted-to-experimental ratios ranging from 0.86 to 1.16.