Research On Shear Behavior Of BFRP-Reinforced Concrete Deep Beams Without Stirrups

In order to solve the problem of durability reduction of concrete structures caused by steel corrosion and improve the service life of structures,fiber reinforced polymer(FRP)is more and more widely used in civil engineering.Compared with traditional steel bars,FRP bars have the advantages of light weight,high strength,corrosion resistance and fatigue resistance,which make them very suitable for engineering structures serving in corrosive environment,such as highway,bridge,harbour engineering and other deep beam structures,and basalt fiber reinforced polymer(BFRP)bars have more stable physical and chemical properties and high cost performance.Therefore,the application of BFRP bars instead of steel bars in practical projects has good economic and social benefits,and there are engineering examples and relevant technical specifications.In recent years,fiber reinforced concrete has attracted much attention because of its excellent mechanical properties and crack resistance.Basalt fiber is a new type of inorganic fiber material,which has high tensile strength,good crack resistance,corrosion resistance,high temperature resistance,good chemical stability and high modulus of elasticity.Basalt fiber reinforced cement matrix composites made by mixing short basalt fiber into cement matrix have many excellent properties and are good substitutes for other fibers.There are few reports about the influence of basalt fibers on the shear behavior of BFRP reinforced concrete deep beams without stirrups,therefore,it is of great significance to study the shear behavior of BFRP bars basalt fiber reinforced concrete deep beams without stirrups.In order to study the influence of different shear span ratio,reinforcement ratio of BFRP bars,effective height of section,compressive strength of concrete,characteristic parameters of basalt fiber on mid-span deflection,cracking load and ultimate load,shear tests of 9 normal concrete and 4 basalt fiber reinforced concrete deep beams reinforced with BFRP bars are carried out under the action of four points,and the crack development,failure mode,the strain of longitudinal reinforcement and concrete during the test are analyzed and studied.The results show that the mid-span deflection of test beams increases with the increase of shear span ratio,decreases with the increase of reinforcement ratio of BFRP bars,effective height of section and characteristic parameters of basalt fibers under the same load,while the compressive strength of concrete has no obvious effect on the mid-span deflection of test beams;the cracking load and ultimate load of test beams decrease with the increase of shear span ratio,and increase with the increase of reinforcement ratio of BFRP bars,effective height of section,compressive strength of concrete and characteristic parameters of basalt fiber.Based on the test data,the shear capacity of BFRP reinforced concrete deep beam is calculated and analyzed according to the relevant national concrete structure design codes.The results show that the strut-and-tie model of ACI 318-11 code is more reasonable in calculating the shear capacity of BFRP reinforced ordinary concrete deep beams,and the calculated values of BFRP reinforced basalt fiber reinforced concrete deep beams based on GB 50010-2015 code are basically in agreement with the experimental values.The mid-span deflection and maximum crack width of BFRP reinforced ordinary concrete deep beam are calculated and analyzed according to the codes for design of FRP reinforced concrete structures in different countries.The results show that CSA S806-12 code is more reasonable in calculating the mid-span deflection of test beams,and GB 50608-2010 code is better than ACI 440.1R-06 code in calculating the maximum crack width of test beams.