Flexural Behavior Of RC Beams Strengthened By BFRP Bars Reinforced With ECC Matrix

The flexural capacity of concrete beams with suitable steel bars is insufficient especially due to the cracking of concrete and the corrosion of steel bars in the coastal area under harsh service environments.In order to improve the flexural capacity and deformation of reinforced concrete beams as well as improve the durability of the concrete structures after strengthening,this paper combines fiber reinforced polymer composite(FRP)and ultra-high ductility cement-based composites(ECC)with perfect durability to strengthen reinforced concrete beams,and studied the flexural behavior of the RC beams strengthened by BFRP / high strength steel(HSS)reinforced with ECC,and the results are presented as follows.(1)The success of strengthening and repairing concrete structures is mainly depends on the interface performance between concrete and cement-based materials.In order to ensure the good interface performance between concrete and ECC,we firstly studied the shear test of the interface of ECC-concrete,and the double shear tests was used to verify the effectiveness of different interface treatment methods to improve the interface bond performance of ECC-concrete.In this experiment,four groups of ECC concrete bond shear tests were designed and including three specimens of each group.The treatment methods of concrete interface include roughing treatment,steel bolt anchorage,bonding epoxy adhesive as well as smooth interface.The ultimate shear strength and displacement of ECC-concrete interface were obtained from the discussion of the test results,with the purpose of providing possible ECC-concrete interface treatments using in flexural strengthening RC beams.(2)The flexural behavior of RC Beams Strengthened with BFRP/high strength steel bars and ultra-high ductility cement-based composite(ECC)was tested.Eight strengthened beams and one control beam were designed and tested in the four point bending test and the analysis of the results were completed.The design,fabrication process,test loading as well as the measurements of the specimens were presented in detail,and the main results include the failure modes and crack development of the specimens.Then the load-displacement behavior of each strengthened beam as well as the strain of the steel reinforcement and BFRP/HSS bars were completed in this section.In order to further explore the advantages of this method,the crack control mechanism of RC beams strengthened by BFRP ECC composite reinforcement is discussed.(3)The design idea and formula of RC beams strengthened by BFRP/HSS bars reinforced with ECC matrix was presented based on the basic assumption of plane cross-section assumption.According to the three possible failure modes and two corresponding limiting failure types of the strengthened beams,the calculation formula of flexural bearing capacity of the strengthened beams is derived,and the bearing capacity,failure mode and ultimate stress of BFRP/HSS bars are derived by theory.The rationality of the results is further analyzed based on the comparison between the experiment data and the theoretical analysis.