Flexural Performance Of GFRP-steel Composite Reinforced Sea Sand Concrete Beams

Fiber reinforced polymer(FRP)has the advantages of light weight,high strength,corrosion resistance and fatigue resistance.FRP bars can replace steel bars in concrete structures,especially in sand concrete structures.However,for FRP bar,due to their small stiffness and brittle fracture mode,there are problems of insufficient stiffness and brittle failure of FRP bars flexural concrete members.In order to solve the problem that steel bars are easy to corrode in seasand concrete flexural members,while FRP bars are not enough rigidity and brittle failure,a new type of composite steel bars with glass fiber reinforced plastics(GFRP)-steel bars(inner core is steel bars,outer layer is encapsulated with GFRP,hereinafter referred to as composite steel bars)is introduced as the force bars of seasand concrete beams,and the composite steel bars with GFRP-steel bars are used as the force bars of seasand concrete beams.Condensate beams are taken as research objects,and four-point bending tests of marine sand concrete beams with different thickness of fiber wrap and different reinforcement combination are carried out.Compared with traditional reinforced concrete beams and FRP reinforced concrete beams,the failure modes and flexural properties such as deflection,crack and bearing capacity of GFRP reinforced concrete beams with marine sand are discussed.It is proposed that GFRP reinforced concrete beams with marine sand are different from those with conventional reinforced concrete and FRP reinforced concrete beams.The calculation reference of stage deflection,crack and bearing capacity.The main contents and conclusions of this paper are as follows:(1)Failure modes of GFRP reinforced concrete beams with sea sand.Four-point bending tests were carried out on concrete beams reinforced with different ratios of steel bars and GFRP materials,and the effects of the ratio of steel bars to GFRP materials on the stiffness and ductility of sea sand concrete beams were discussed.The results show that: 1)the stiffness of GFRP reinforced concrete beams with sea sand has three obvious changes,namely,before concrete cracking,concrete cracking to steel bar yield and steel bar yielding to composite bar fracture;2)Increasing the reinforcement ratio without considering the defects of steel bar corrosion is conducive to improving the stiffness and ductility of sea sand concrete beams.(2)Calculating method of deflection and crack width of GFRP reinforced concrete beams with sea sand.Deflection and crack width of sea sand concrete beams with different ratios of steel bars and GFRP materials under four-point bending are measured.The deflection and crack width of GFRP-steel composite bars are calculated by combining the calculation methods of deflection and crack width of concrete beams with steel bars and FRP bars in ACI318-05 and ACI440.1R-15 codes,and compared with the experimental results.The results show that: 1)for the deflection calculation of composite reinforced concrete beams with sea sand,the calculated value is smaller than the experimental value,and the yield deflection and ultimate deflection are 16% and 13% smaller than the theoretical value;2)for the crack width calculation of composite reinforced concrete beams with sea sand,the calculated value is smaller than the experimental value,and 25% smaller on average;3)for the calculation of the deflection and crack width of composite reinforced concrete beams with sea sand,it is necessary to consider.Consider the reduction of elastic modulus of composite tendons.(3)The calculation method of yield and ultimate bearing capacity of GFRP-Steel composite reinforced concrete beams with sea sand.Based on the calculation method of ultimate bearing capacity of FRP reinforced concrete beams in ACI440.1R-15 code,the corresponding formulas are deduced according to the deformation coordination principle and force balance principle,and the theoretical results are compared with the experimental values.The results show that: 1)For the yield load calculation of composite reinforced sea sand concrete beams,the mean value of the ratio of test value to calculated value is 1.0;2)For the ultimate bearing capacity calculation of composite reinforced sea sand concrete beams,the mean value of the ratio of test value to calculated value is 1.08;3)The theoretical model of bearing capacity of composite reinforced sea sand concrete beams established in this paper is in good agreement with the experimental results.