This study investigated the post-fire seismic characteristics of reinforced concrete frame joints with carbon fiber-reinforced polymer (CFRP) under low-cycle reciprocating loads through numerical analysis. Finite element simulations were conducted to examine the hysteretic curve, skeleton curve, energy dissipation, and stress distribution of the reinforced joints. The findings revealed that, relative to unreinforced joints post-fire, the bearing capacity of the reinforced joints remained essentially unaltered during the elastic phase. However, their ultimate bearing capacity, energy dissipation capacity, and ductility exhibited varying degrees of enhancement. Interestingly, this augmentation did not persist as the number of reinforcement layers increased. The optimal reinforcing effect was observed with the application of two reinforcement layers, resulting in a 30.3% increase in ultimate bearing capacity and a 26.5% improvement in energy dissipation capacity. Moreover, as the axial compression ratio increased, the high-stress zones within the joint expanded, and the failure mode transitioned from plastic damage at the beam end of the joint under low axial compression ratios to column crushing failure under high axial compression ratios.
Steel was used to reinforce the joint of the frame after fire, and the joint was subjected to low cyclic loading. The seismic behaviors including hysteretic curve, skeleton curve, energy dissipation and stress distribution were analyzed using the finite element method. The results show that the bearing capacity in the elastic stage is almost unchanged comparing with the non-reinforced joint, but the ultimate bearing capacity, energy dissipation capacity and ductility are all improved in different degrees. However, the strengthening effect is not unlimited with the increase of the thickness of bonded steel. The thickness of bonded steel should not exceed 6 mm considering the ultimate bearing capacity, energy dissipation capacity and stress distribution of the structure. The area of high stress zone increases with the increase of axial compression ratio.
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