Experimental study on the flexural behaviour of notched steel beams strengthened by prestressed CFRP plate with an end plate anchorage system

Strengthening deficient steel structures using prestressed bonded Carbon Fibre Reinforced Polymer (CFRP) plate could be a promising technology, but has not been well developed yet due to the lack of a proper CFRP prestressing device. In this study, notched steel beams strengthened with prestressed CFRP plate with end anchorage systems were designed and experimentally studied. The prestress loss and flexural behaviour of the strengthened steel beams were investigated. With the aid of strain gauges and Fibre Bragg Grating (FBG) sensors, the prestress loss in specimens with prestress levels of 20% and 40% were monitored during tensioning, release and a mid-long period after release. There is almost no prestress loss for specimens after 30 days of release, which indicates that the end anchorage system can effectively impede prestress loss. From the four-point bending test results, the bearing capacity and utilization ratio of the CFRP plate, effect of prestress on the flexural performance and failure modes were discussed. The prestressed strengthening can improve the bearing capacity and ductility of deficient steel beams, and increases the utilization rate of CFRP plate, while the enhancement of the stiffness is not obvious. Additionally, the bearing capacity of the specimens and utilization rate of the CFRP increase with the prestress level. More importantly, the prestressed strengthening can delay debonding propagation of the strengthened beams, preventing premature failure.