Strengthening effect of the CFRP method on fire-damaged segments

• CFRP method can improve mechanical performance of fire-damaged segments. • CFRP method promotes load-bearing behaviour but at the expense of deformation ability. • CFRP grid has a higher utilization rate of tensile properties than CFRP sheet. • CFRP-sheet method exhibits superior initial stiffness compared to CFRP-PCM method. To reveal the strengthening effect of the CFRP method on the fire-damaged segment. In this study, the fire-damaged segment was strengthened with the CFRP-PCM method and CFRP-sheet method, respectively. The crack development, deformation characteristics, failure mode, load-bearing behaviour and internal force evolution of the segment specimens were analysed. The results indicated that the CFRP-PCM method can improve the crack development of the segment, while the CFRP-sheet method can only prevent the crack initiation of the segment before tearing between the CFRP sheet and the segment. The fire-damaged segment strengthened by the CFRP-PCM method exhibited gradual deformation and failure characteristics, whereas the fire-damaged segment strengthened by the CFRP-sheet method exhibited sudden failure with no discernible damage characteristics. The CFRP-sheet method had a higher initial strengthening effect on the fire-damaged segment than the CFRP-PCM method before tearing between the CFRP sheet and the segment, while the strength utilisation rate of the CFRP grid was higher than that of the CFRP sheet. The CFRP method of strengthening the fire-damaged segment can improve the tensile strength of the tension zone, increase the sectional stiffness, and restore the load-bearing capacity; however, this comes at the expense of the deformation capacity. The study provides a reference value for the strengthening design of fire-damaged linings in shield tunnels.