Bearing Capacity Of High Strengthened Concrete Beams With Prestressed CFRP Under Freeze-Thaw Cycles

Concrete building is one of the most common buildings in China.Due to many factors such as bad environment and continuous load and aging,concrete buildings would appear structural damage during long-term service.In view of this,Strengthening and repairing these buildings is an efficient and economic way to avoid huge deficit caused by demolition and reconstruction.CFRP plays a significant role in the field of repairing concrete technology due to its light weight and convenient construction.Moreover,the utilization of CFRP has been greatly improved by using beams reinforced with prestressed CFRP.In the north of China,freeze-thaw environment is a kind of hazardous environments.The freeze-thaw cycles affect the structures strengthened with CFRP.There are not many researches on prestressed specimens and high strength concrete.Therefore,it is important to study the mechanical behavior changes of the beams strengthened with CFRP under freeze-thaw cycles.Supported by the National Natural Science Foundation of China,this paper analysis the influence of freeze-thaw cycles and prestresing on the bearing capacity of beams strengthened with prestressed CFRP.The results are as follows:(1)The effect of short-term freeze-thaw cycles on the bearing capacity of test beams strengthened with CFRP.The results revealed that bearing capacity of specimens did not change obviously after 25 cycles.With the increase of freeze-thaw cycles,the ultimate load and ultimate deflection of the specimens dropped to some extent.Shear failure and local shear failure belonging to brittle failure occurred in some prestressed specimens under short-term freeze-thaw cycles.In order to avoid brittle failure,it is important to improve the shear capacity of the beams strengthened with prestressed CFRP in practical engineering.(2)The flexural behavior of beams strengthened with different levels of prestress under freeze-thaw cycles.The results revealed that after the action of freeze-thaw cycles,the ultimate load and cracking load and ultimate deflection of the specimens decreased obviously and the ultimate strain value also decreased rapidly.The more the times of freeze-thaw cycles was,the greater the decrease was.Under the same times of freeze-thaw cycles,the higher the prestressing grade was,the more significant the flexural behavior of the specimens decrease was.The interfaical bonding performance also decreased obviously under freeze-thaw cycles.After the freeze-thaw cycles,the location of the failure surface of the specimens gradually transformed from the concrete surface to the concrete-resin interface and tend to transformed from concrete-resin interface to resin-CFRP interface.(3)The deterioration of beams strengthened with CFRP under long-term freeze-thaw cycles.The results revealed that the carrying capacity of specimens decreased seriously after 500 cycles.Under long-term freeze-thaw cycles,the ultimate load and cracking load and bending stiffness and CFRP ultimate strain value of the prestressed specimens decreased more obviously than those of the non-prestressed specimens.The interfaical bonding performance of the prestressed specimens decreased heavily.The location of the failure surface of the prestressed specimens transformed from concrete-resin interface to resin-CFRP interface under long-term freeze-thaw cycles.