Study On Bending Performance Of New Steel-FRP Composite Bar Ultra-High Performance Concrete Beam

Reinforced concrete structures are widely used in the civil engineering industry and have many advantages.However,with socio-economic development,China’s civil engineering construction is gradually moving from the inland to the sea,resulting in huge changes in the use environment of reinforced concrete structures.At the same time,due to the characteristics of both reinforcement and concrete,the traditional reinforced concrete structure is prone to insufficient load-bearing capacity and durability problems due to corrosion of reinforcement and poor crack resistance of concrete,leading to the destruction of concrete structures.The durability problems of traditional structural forms have promoted the development of FRP concrete structures.However,FRP materials are linearly elastic and lack a yield plateau,so brittle damage with poor ductility usually occurs in FRP concrete structures.Steel-FRP Composite Bar(SFCB)formed on this basis has the characteristics of high strength,high ductility,higher elastic modulus,stable secondary stiffness,and superior durability performance.Therefore,the combination of SFCB and Ultra-High Performance Concrete(UHPC),which has high compressive and tensile strength,good ductility and superior durability,is considered to form a new type of concrete structure,which can improve the dilemma of inadequate load-bearing capacity and durability of conventional structures.In order to study the flexural performance of the new steel-FRP composite reinforced ultra-high performance concrete beams,this paper investigates the following four aspects,and the research results will provide some reference for the application of UHPC,SFCB and SFCBUHPC beams in practical projects.The main research contents are as follows:(1)The reasonable and cost-effective UHPC ratio was selected by drawing on the existing UHPC ratio of the subject group.Conduct material property tests on UHPC to obtain the mechanical properties of UHPC;conduct standard pull-out tests on the bonding performance of UHPC and SFCB,analyze the bond-slip curve of SFCB and UHPC,and obtain the principal structure model of bonding and anchoring of SFCB and UHPC.(2)The SFCB-UHPC beams were tested in static bending performance and compared with steel reinforced UHPC beams and BFRP reinforced UHPC beams to verify the superiority of SFCB-UHPC beams in bending performance;the effects of three parameters,namely concrete strength,SFCB type and reinforcement rate,on the damage pattern,bearing capacity,stiffness,cracking and ductility of SFCB-UHPC beams were investigated.The results show that the ultimate bearing capacity of the test beam increases with the increase of concrete strength,and the ultimate bearing capacity of the UHPC beam is 3.2 times and 2.0 times of that of the normal concrete beam and the high-strength concrete beam respectively,and the flexural bearing capacity of the UHPC beam with fine aggregate of machine-made sand is increased by 14.6%because the strength of UHPC is higher than that of UHPC with fine aggregate of quartz sand.When the reinforcement rate was increased from 1.30%to 2.16%,the ultimate bearing capacity of the test beam was increased by 27%,indicating that increasing the reinforcement rate can improve the ultimate bearing capacity of SFCB-UHPC beam when the SFCB type is the same;comparing the UHPC beams with different longitudinal reinforcement types,the results show that the ultimate bearing capacity of BFRP reinforced UHPC beam is higher than that of SFCB-UHPC beam,while the ultimate bearing capacity of steel reinforced UHPC beam is the lowest.The ultimate bearing capacity of SFCB-UHPC beam is 27%higher than that of steel UHPC beam;when the reinforcement ratio of each test beam is 1.30%,the stiffness of BFRP UHPC beam is the smallest and the deflection is the largest under the same level of load,while the steel UHPC beam is the opposite,and the SFCBUHPC beam is between the two.The SFCB-UHPC beam has both high loads carrying capacity and good deformation performance.(3)The full process analysis of SFCB-UHPC beams subjected to bending performance,based on the simplified SFCB and UHPC principal structure models and basic assumptions,the discriminative method of SFCB-UHPC beam damage morphology,the derivation of the calculation formulae of cracking,yielding and ultimate load of SFCB-UHPC beams and the calculation methods of stiffness and crack width.(4)The use of finite element software ABAQUS to the bending performance of SFCBUHPC beams simulated using the finite element software ABAQUS,and the outer clad fiber modulus of elasticity,inner core reinforcement to SFCB area ratio and core steel bar strength grade was selected for analysis to explore the effects of each parameter on the load carrying capacity and deformation performance of the bending beams.The results show that the yield and ultimate loads of the specimens increase with the increase of the modulus of elasticity of the clad fiber,energy dissipation and ductility decrease with increasing modulus of elasticity of the outer wrapped fibers;the larger the area ratio as of the inner core reinforcement to SFCB,the higher the yield load of the specimens,while the ultimate load decreases with the increase of as,energy consumption and ductility decrease with the increase of as;the higher the strength grade of the inner core reinforcement of SFCB,the higher the yield and ultimate loads of the specimens,energy consumption increases with the strength grade of the inner core reinforcement and the ductility inversely.(5)Based on the compressive and tensile principal structure of UHPC and the uniaxial tensile SFCB principal structure under the action of freeze-thaw cycles,the bending capacity analysis of SFCB-UHPC beams under the action of freeze-thaw cycles was carried out by using the finite element software ABAQUS.The results show that the concrete strength has a great influence on the durability performance of SFCB-UHPC beams,and the higher the concrete strength is,the more times the specimen can withstand freeze-thaw cycles;the ultimate bearing capacity of each specimen after 800 freeze-thaw cycles is from high to low,in the order of BFRP reinforced UHPC beams,SFCB-UHPC beams and steel reinforced UHPC beams;the ultimate bearing capacity and deflection of each specimen decrease with the increase of concrete;the greater the thickness of the protective layer of concrete,the lower the attenuation of the specimen after freeze-thaw cycles;the ultimate bearing capacity and deflection of each specimen decreased with the increase of the number of freeze-thaw cycles.