Study On The Bending Performance Of Steel Reinforced Concrete Beams Strengthened By Prestressed And Externally Bonded BFRP Plates

Bridge reinforcement has a wonderful development prospect for the reasons that a large number of bridges have become dangerous bridges and the national highway network needs to be upgraded.Fiber Reinforced Polymer/Plastic(FRP)is high-strength and light-weighted.Taking FRP as pre-strssed material for prestrssed reinforcement method can effectively improve the performance of the sick bridges.Reinforcement method of Carbon Fiber Reinforcement Polymer/Plastic(CFRP)has been widely applied in the field of bridge reinforcement.But CFRP is a kind of material that is pricy and has low elongation.Basalt Fiber Reinforced Polymer/Plastic(BFRP)is a new kind of material with environmental protection,cost-efficiency and high economic benefits.Therefore,BFRP has good application prospects in the field of pre-stressed FRP reinforcement.However,the systematic research concering reinforcement method of pre-stressed BFRP plate is rare both at home and abroad.In this paper,the research will be implemented from the mechanical properties of BFRP plate,the tension and anchorage technology of BFRP plates and beams strengthed by pre-stressed BFRP plates: 1)to evaluate the tensile and shear properties of BFRP plates;2)to study the tension and anchorage technology of pre-stressed BFRP plates;3)to evaluate the static properties of reinforced concrete(RC)beams strengthened by pre-stressed BFRP plates,and to put forward the corresponding design and analysis methods.(1)Study on BFRP plates and its tension and anchorage technology.According to the test results of mechanical properties of BFRP plates,the tensile strength of BFRP plates with thickness of 2 mm and 5 mm both more than 1300 MPa,which exceeds 50% of the standard strength of CFRP plates(2400 MPa)stipulated by the code.The tensile elongation at break of BFRP Plate is more than 2.4%,which is larger than that of CFRP plate(1.9%).BFRP is expected to obtain larger deformation when applied in structures.The elastic modulus of BFRP plate exceeds 52.5GPa,which is about 1/3 of that of CFRP plate.The static performance of CFRP plate and BFRP plate-anchorage assemblies were tested by both the Fatigue Machine and the Fixed Support.The static load test results of Fatigue Machine BFRP plate-anchorage assemblies show that the anchorage efficiency coefficient of BFRP plate anchorage with 50mm×5mm section is 83.2%,and the plates showed blasting failure.The anchorage efficiency coefficient of CFRP plate anchorage assembly with 50mm×2mm section is 71.60%.The assembly was failed by CFRP plates sliding.The static load test results of Fixed Support BFRP plate-anchorage assemblies showed that the ultimate strength of CFRP plate-anchorage assembly with section 50mm×2mm is 2420 MPa and the efficiency coefficient of anchorage is 78.1%.The ultimate strength of BFRP plate-anchorage assembly with section 50mm×2mm is 1150 MPa and the efficiency coefficient of anchorage is 88.5%.Therefore,the anchorage can well achieve the perfromance of BFRP plates and CFRP plates.(2)Static performance test of RC beams strengthened by pre-stressed BFRP plates.The flexural behavior of RC beams strengthened by pre-stressed BFRP plates was studied through static tests of two unreinforced beams,one beam strengthened by ordinary BFRP plate and seven beams strengthened by pre-stressed FRP plates.The test results show that the mechanical properties of the beam strengthened by pre-stressed BFRP plate with thickness 5mm is similar to the beam strengthened by pre-stressed CFRP plate with thickness 2mm.As for beams strengthened by pre-stressed BFRP plates,the larger the amount of reinforcement,the higher the cracking load,yield load and ultimate load,but the the degree of prestressing loss would be higher too.Beams strengthed by greater amount of reinforcement would show more obvious brittle failure characteristics,while beams strengthed by less amount of reinforcement can still maintain a higher level of bearing capacity after deformed largely.The greater the tension control stress,the higher the yield load and ultimate load of the test beam,the strength efficiency of FRP plate and the stiffness of the test beam would be greater too.Viscose has little effect on the yield load and ultimate load of the test beam,but the cracking load of the beam without viscose is higher.Beam with lower reinforcement ratio shows higher reinforcement effect.The crack development speed of the less-reinforced beam is higher than that of the suitable-reinforced beam,and the strength efficiency of the FRP plate of the suitable-reinforced beam is higher than that of the less-reinforced beam.(3)Research on the design method of RC beams strengthened by pre-stressed BFRP plates.The cracking load,yield load and ultimate load of RC beams with rectangular section and T-section before and after strengthening are systematically calculated and analyzed.The internal forces of RC beams strengthened by pre-stressed FRP plates under the conditions of post-tensioning,decompression,cracking and ultimate bearing capacity are analyzed,and the formulas for cracking moment,yield moment and ultimate bending moment are proposed.Except for cracking moment,the calculated and experimental values of yield moment and ultimate moment are in good coincidence.The theory is applicable to the calculation for the bearing capacity of unreinforced beams and reinforced beams strengthened with pre-stressed BFRP plates,while the theoretical analysis of beams strengthened by ordinary BFRP plates and less-reinforced beam strengthed by pre-stressed BFRP plates still needs further study.In conclusion,the superior mechanical properties of BFRP plate are clarified by the research above.In addition,the static performance of the beam strengthened by pre-stressed BFRP plate with thickness 5mm is similar to or even better than the beam strengthened by pre-stressed CFRP plate with thickness 2mm.The design method of beam strengthened by pre-stressed BFRP plate has been put forward.These efforts would provide some experimental and theoretical basis for BFRP who is cost-effective,environmental friendly and has excellent mechanical properties to be used in field of bridge reinforcement.