Impact performance of fire-damaged hybrid steel-BFRP reinforcement concrete beams: Influence of area ratio and arrangement of BFRP bars

Abstract

Hybrid steel-BFRP reinforced concrete (HRC) beams have demonstrated their ability to meet the rigorous demands for both strength and serviceability. However, the mechanical properties of HRC beams under fire accompanied by impact loadings are not yet clear. In order to delve into the impact resistance of HRC beams under high temperatures, a three-dimensional numerical model was crafted to account for both the effects of strain rate and temperature degradation. The study aimed to examine how the impact resistance of HRC beams is influenced by varying area ratios and arrangements of BFRP bars. The model's reliability was ascertained through a comparison between its simulation outcomes and the results of physical tests. The results show that HRC beams exhibit a significant reduction in stiffness, impact and internal force under fire conditions (39 %, 38 % and 72 % for a fire duration of 45 min, respectively). Furthermore, the damage is concentrated in the mid-span. The impact performance of HRC beams at room and high temperatures is between those of pure steel-RC beams and pure-BFRP beams. The variations under the same fire conditions in the displacement and internal force of beams with different BFRP bars area ratios reach 70 %, while with different arrangements of BFRP bars do not differ much (within 20 %). The dynamic to static stiffness ratio and ultimate load ratio is reduced following the growth of BFRP bars area ratio (max. gap up to 56 % and 25 %) and fire time (max. gap up to 15 % and 20 %). Therefore, specimen design prioritizes the bar arrangement with better corrosion resistance. Additionally, the residual bearing capacity of HRC beams is only 10–40 % of the original under 45 min fire duration. The association of residual load capacity and displacement with fire time shifted from linear to nonlinear with rising temperature.