Effects of FRP Repair on Fatigue Strength

Figure 5 shows the fatigue life vs. load range for flexural and bond specimens. The life-load range variation of bond-beams is presented in Figure 5a. In set B-CD (with a 5% mass loss due to corrosion) the fatigue bond strength decreased by 23% and 15% compared to the control (uncorroded) beams at 3,000 cycles and 50,000 cycles respectively. The decrease was less at low load ranges (high fatigue lives) than at higher load ranges (lower fatigue lives). When CFRP sheets were added to strengthen the beams an increase of 15 % in fatigue bond strength compared to the fatigue strength of the cor­roded unstrengthened beams was achieved. This increase was about the same at all fatigue lives. It should be noted that CFRP sheets at long fatigue lives were able to restore the original uncorroded fa­tigue strength of the beams.

The variation of the fatigue life with the load range applied on flexure-beams in Figure 5b. The fa­tigue strength in set F-CD flexural beams was reduced by approximately 10% compared to those of set F-C. Repairing the 5% corroded beams with CFRP (set F-CR) increased the fatigue strength of the beams by 10% at 100,000 cycles and by 18% at 750,000 cycles compared to the corroded unrepaired beams (set F-CD). It should be noted that repairing with CFRP sheets restored the fatigue flexural strength of the corroded beams to a level equal to that of the original uncorroded beams.


Figure 5. Variation of the fatigue life with load ranges: a) bond beams, b) flexure beams