Post-Fire Compressive Behavior of CFRP Stirrups Reinforced CFST Columns: Experimental Investigation and Calculation Models

This paper investigates the post-fire compressive behavior of CFST columns reinforced with CFRP strip stirrups. CFRP materials possess higher tensile strength than steel, making them promising candidates to enhance the ductility of high strength concrete when properly confined. However, direct exposure to fire leads to burning and rapid loss of tensile capacity in CFRP materials. To mitigate this, the study explores embedding CFRP stirrups in concrete to provide additional confinement besides the steel tube which prevents fire penetration through concrete cracks and protects the CFRP stirrups. Through experimental tests and comparisons with steel stirrups reinforced counterparts, it was observed that the CFRP stirrups, even after heating, still provided confinement to the concrete core as the overlapping joints of the strips remained intact. The failure mode observed in the CFRP stirrups was the rupture of FRP, rather than debonding of overlapping joints. Additionally, the use of CFRP stirrups led to reduced concrete temperatures and significantly higher unit enhancement in residual load-bearing capacity for the CFST columns compared to steel stirrups. Practical calculation models were developed to estimate the historical maximum temperatures and residual load-bearing capacity of the CFRP stirrups reinforced CFST columns, regardless of whether high strength or normal strength concrete was used. The calculated values demonstrated good agreement with experimental results. This study provides valuable insights into the performance of CFRP stirrups reinforced CFST columns under post-fire conditions, highlighting their potential as effective fire-resistant and structurally efficient solutions in civil engineering applications.