Evaluation of bond properties of degraded CFRP-strengthened double strap joints

The application of CFRP has become a popular strengthening technique for retrofitting of metallic structures. However, knowledge is very limited on the durability of CFRP composites under different environmental conditions. This paper presents the outcomes of a research program on the bond characteristics and environmental durability of degraded CFRP-strengthened steel plate double strap joints. Investigations were carried out on failure mode, ultimate load, joint strength, effective bond length and the effect of embedded GFRP layers for double strap joints. Shear stress-slip curves were developed for degraded CFRP-steel composite using the experimentally measured strain data. Results show that the failure modes and joint capacities are highly dependent on the number of CFRP layers utilised in the composite systems under environmental conditioning. The use of embedded GFRP layers can improve the long-term durability of the composite system. However, optimum structural properties could not be achieved using embedded GFRP as the innermost layer. The bond-slip responses for degraded CFRP double strap joints were shown to have an approximately bilinear relationship.