Abstract:Fatigue damage is the main cause of the deficiency of steel structures.Traditional steel structure strengthening methods,which include steel plate welding,rivet connecting,bolting and so on,tend to cause stress concentration.CFRP has high strength and rigidity,and CFRP strengthening has unique advantage of strengthening steel structure in contrast to the traditional retrofit methods.Through fatigue tests on three groups of open-hole steel plates with CFRP strengthening,fatigue failure mode were described and related fatigue life and deformation curves were analyzed.Similarities and differences were compared in fatigue life,crack growth,cooperative working condition between three groups of steel plates and CFRP.It was found that the yielding load of the repaired specimens increases obviously,the flaws on the surface of steel plate could be repaired and crack propagation speed could be slowed with the use of CFRP strengthening. The ductility and fatigue life could also be increased.With the increase of the number of CFRP layers,the fatigue life could be improved by 4.7% and 77.8% with one layer CFRP and three layer CFRP.The results showed that the carbon fiber sheets reduce the difference between the deformability of the steel plate under different stress effectively.The difference decreased when the CFRP increased.Observation showed that the more CFRP stickup layer the steel plate had,the bigger its limit deformation against broken was.The limit deformation to steel plate with three-layer carbon fiber sheet was above 0.9 mm.