Flexural behaviour of notched steel beams strengthened with a prestressed CFRP plate subjected to fatigue damage and wetting/drying cycles

Abstract Applying a prestressed Carbon Fibre Reinforced Polymer (CFRP) to strengthen deficient steel structures is a favourable approach. However, fatigue loading and hygrothermal exposure can weaken adhesive bonding. A theoretical analysis of the interfacial stress distribution at the notch location was first carried out to explain the mechanism of delay of the interfacial debonding of notched steel beams after prestressed CFRP strengthening. Then, the prestress loss and flexural behaviour of specimens (with a prestress level of 25%) subjected to fatigue damage (FD) and/or wetting/drying cycles (WDCs) with 3.5 wt% NaCl solution were further experimentally investigated. Theoretical results showed that prestressed CFRP strengthening can significantly reduce the interfacial stress at the notch site and delay interfacial debonding. The CFRP prestress loss mainly occurs in the hardening stage of the adhesive layer, and the total prestress loss is less than 2.7% for specimens subjected to WDC exposure, indicating the effectiveness of the end anchorage system. The adhesive microcracks at the notch induced by FD and adhesive bonding degradation caused by WDCs significantly affect the interfacial debonding. In addition, NaCl solution penetration accelerated by microcracks causes further degradation of interfacial bonding. Nevertheless, the end anchorage system showed promising stiffness and load-carrying capacity behaviour for the specimens subjected to FD, WDCs, and the combined effects. The mixed failure mode of CFRP fracture and CFRP extraction from the end anchorage demonstrates that the strength of the CFRP plate was thoroughly utilized for the specimens with prestressed CFRP.