Upgrading of precast RC beam-column joints using innovative FRP/steel hybrid technique for progressive collapse prevention

Abstract

This study aims at investigating the efficacy of using an innovative hybrid strengthening technique composed of near-surface mounted (NSM) steel rebars along with fiber reinforced polymer (FRP) sheets to prevent (or diminish) the risk of progressive collapse in precast reinforced concrete (RC) beam-column joints. The study details tests involving one control specimen that is a half-scale single-story precast RC beam-column assembly having two bays. One monolithic test specimen with continuous longitudinal beam rebars was employed for comparison. The third specimen was similar to the control one, but it was retrofitted using FRP sheets combined with NSM steel rebars within the beam-column joint zone. The base of the center column was released, and a dynamic load was applied in the vertical direction on this column for simulating the column-removal scenario of progressive collapse. The proposed strengthening technique was efficient at enhancing the peak load and dissipated energy of the upgraded specimen by about 16.9 and 12.4 times, respectively, of control precast specimen. Three dimensional (3D) finite element (FE) models that consider rate-dependent material nonlinearity and bond behavior at FRP-to-concrete interface were also devised to predict the behavior of test specimens. Good agreement was obtained between the experimental and FE results with prediction errors ranging from 0% to 4%, 1% to 17%, and 3% to 10% for peak load, center column displacement at peak load, and dissipated energy at ultimate state. The validated FE models were employed for parametric studies of practical interest for investigating the impact of different strengthening parameters on the behavior of test specimen under the middle column-loss scenario.