Experimental Study On The Flexural Capacity Of Notched Steel Beams Strengthened With Prestressed CFRP Plate

Steel structure inevitably exist a variety of injuries and defects in long-term service.CFRP material has widely been used to repaire defect steel structure,which can make full use of the advantages of CFRP,including high strength、corrosion resistant,and also convenient to construction.To improve the bearing capacity of defect steel beam,the common repairing method is sticking CFRP material to the tension flange of steel beam.However,the cases of lacking CFRP end anchorage usually leads to CFRP debonding early,which reduces the utilization rate of CFRP and causes great waste.In this paper,an experimental study on notched steel beam strengthened with prestressed CFRP plate with end anchorage was conducted.The main contents and conclusions can be seen as follows:(1)Research on the pre-stress loss of notched steel beam strengthened with prestressed CFRP plate with end anchorage.By use of strain gauge and fiber bragg grating sensor,the pre-stress change of specimens with pre-stress level of 20% and 40% were monitored in the process of tensionin,releasing and a mid-long period after tensioning,releasing.The results shows that: end anchorage of CFRP plate can effectively reduce the prestress loss.At the very time of tensioning,releasing,the average ratio of prestress loss of CFRP plate are 0.91% and 0.73% respectively.After tensioning,releasing,the prestress loss of CFRP plate mainly occurs in the first 30 days,since then,there is almost no pretress loss.The total prestress loss of P-20%-3 beam and P-40%-3 beam are 1.60% and 1.43% respectively.(2)Static testing different forms of steel beams and compare their load-deflection curve,load-strain curve and analyzing their failure modes.The results shows that: the specimens strengthened with prestressed CFRP plate with end anchorage can delay the crack propagation,improve ultimate bearing capacity,stiffness,ductility and the utilization rate of CFRP plate.compare with specimen strengthened with CFRP plate with end anchorage,the ultimate bearing capacity of the specimens with prestress level of 20% and 40% improves 27.5% and 52.3% respectively,the ultimate utilization rate of CFRP plate improves 25.6% and 39% respectively.(3)Compare the load-strain curves in different location,distribution of CFRP strain under different load,the crack growing process and the failure modes,the results shows that: the damage of the specimens strengthened with pre-stressed CFRP plate with end anchorage starts from defects of the interface layer cracks and CFRP plate debonds,which is caused by the stress concentration at the crack tip.Then the damage develops to the end of CFRP plate,eventually CFRP plate broken near the end anchorage.