Study On Bending Performance Of Steel-FRP Composite Bar Reactive Powder Concrete Protective Frame Beam

The protective structure needs to bear huge impact load,resulting in large cross-section size of the member and occupation of the use area.It is difficult to improve the structural bearing capacity of the traditional reinforced concrete structure on the premise of ensuring the clear height of the structure and the convenience of construction.Steel-FRP Composite Bars(SFCB)and Reactive Powder Concrete(RPC)are high performance building materials with high application prospects in civil engineering field.SFCB has the characteristics of light weight,high tensile strength and stable secondary stiffness,while RPC has the characteristics of high compressive strength.Reinforced RPC with SFCB can form a new type of cementbased structure,which can improve the bearing capacity of the structure without increasing the section size and reinforcement ratio,and realize the large space of the protective engineering.In this paper,the equivalent static bending tests are carried out on the protective frame beams with different concrete types,different reinforcement types and different reinforcement ratios to study the flexural performance of SFCB-RPC protective frame beams.The stress stage analysis of SFCB-RPC protective frame beam is carried out,the calculation formula of the stiffness of the protective frame beam and the maximum crack width of the pure bending section is derived,and compared with the test results.The redistribution of plastic internal forces of SFCB-RPC frame beams is analyzed.The finite element model of the protective frame beam is established by ABAQUS,and the flexure performance is analyzed.The correctness and feasibility of the model analysis are verified by comparing with the experimental results.The influence of various factors on the bending performance of SFCBRPC frame beam is analyzed.In this paper,the main research results are as follows:(1)RPC improves the failure mode of the frame beam and remains intact when crushed.RPC improves the bearing capacity of the frame beam and significantly increases the ratio of the ultimate load to the yield load of the SFCB-RPC frame beam.RPC improves the deformation resistance of frame beam under the same load.In the limit state,the ultimate bearing capacity and deflection of SFCB-RPC frame beams are higher than those of reinforced RPC frame beams.For RPC frame beams,the bearing capacity of FRP bars RPC frame beams is the largest,for ordinary concrete frame beams,reinforced concrete frame beams is the largest.With the decrease of reinforcement ratio,the ultimate load of frame beam decreases and the deformation ability increases.Under different loads,the average strain of concrete at the end and midspan of each frame beam varies linearly along the section height,which is consistent with the assumption of flat section.When the SFCB-RPC frame beam is damaged,the tensile strain of SFCB exceeds 0.017,and the RPC reaches the ultimate compressive strain,and the material strength of SFCB and RPC is fully exerted.RPC reduces the average crack spacing,makes the cracks of frame beams thinner and denser,and reduces the influence of crack development on the strain of reinforcement.The type of reinforcement has great influence on the number and average spacing of cracks in flexural and shear section.With the decrease of reinforcement ratio,the number of cracks increases,the spacing decreases,and the maximum crack width increases under the same load.RPC significantly improves the ductility and energy dissipation of the frame beam,and with the decrease of the reinforcement rate,the ductility and energy dissipation of the frame beam are also improved.The energy dissipation capacity of SFCB-RPC frame beam is better than that of reinforced RPC frame beam.The redistribution of plastic internal forces of SFCB-RPC frame beams is analyzed.(2)Based on the constitutive model of materials and basic assumptions,the stress stage of SFCB-RPC frame beam was analyzed.The cracked steel fibers of SFCB and RPC were converted into the area of RPC material by conversion section method,and the stiffness of section was obtained by effective moment of inertia method According to the design code of concrete structure and considering the influence of steel fiber tension on the maximum crack width,the formula for calculating the maximum crack width of pure bending section is derived.The redistribution of plastic internal forces of SFCB-RPC frame beams is analyzed.(3)Concrete strength has great influence on ultimate bearing capacity,ultimate deflection,ductility,energy dissipation and curvature of SFCB and FRP reinforced concrete frame beams.The concrete strength has little effect on the ultimate load of the RC frame beam and a great effect on the ultimate deflection.With the increase of the ratio of the inner steel bar area to the full section area of SFCB,the load-mid-span deflection curve of the frame beam presents a three-fold line.When the reinforcement material changes from SFCB to reinforcement,the ultimate curvature of the frame beam changes abruptly.The increase of the yield strength of the inner steel bar improves the yield strength of the frame beam,but has little effect on the ultimate load.The influence of the elastic modulus of SFCB on the failure type of the frame beam is significant.When the elastic modulus of SFCB is less than 200GPa,the ultimate deflection,ductility,energy dissipation and curvature of the frame beam decrease with the increase of the elastic modulus of the FRP.The ratio of beam end reinforcement has a great influence on the ultimate load,and the ratio of mid-span reinforcement has a great influence on the mid-span deflection.When the reinforcement ratio of beam end section is greater than that of mid-span section,the energy dissipation capacity of frame beam is improved.With the increase of beam height,the ultimate load of the frame beam increases and the ultimate deflection decreases.When the beam height is 225mm,the ductility and energy dissipation capacity of the frame beam are optimal.When the column side length exceeds 250mm,the influence of increasing the column cross-section size on the ultimate deflection,ductility and energy dissipation capacity is not obvious.In the case of the same bearing capacity,RPC replacing ordinary concrete can not only save the section area of the frame beam but also improve the ductility and energy dissipation capacity of the frame beam.