Research On Short-term Durability Of FRP Bar Reinforced Concrete Beams Under Salt Solution And Stress Coupling

Chloride ions are present in the marine environment,causing severe corrosion to the steel bars,damaging the concrete structure,and reducing the durability of the structure,thereby creating a safety hazard.Aiming at the serious rust problem of reinforced concrete in the marine environment,domestic and foreign experts have carried out a lot of research and adopted a series of anti-corrosion measures,such as cathodic protection method,addition of rust inhibitor method,chloride ion curing method,surface coating method,etc.Although these measures slow down the corrosion rate of steel bars,they do not completely solve the corrosion problem of steel bars.The FRP rib has the advantages of light weight,high strength and corrosion resistance,and can replace the steel bar in the marine environment,effectively solving the problem of steel corrosion.Based on this background,this paper mainly studies the performance of FRP bars,the design method of FRP reinforced concrete beams and the durability of FRP reinforced seawater sand concrete.The main research contents include:(1)The basic mechanical properties and durability data of FRP bars in the literature from 2000 to 2018 were collected.The distribution types and interval of tensile strength,elastic modulus and elongation of FRP bars and its variation with volume percentage and diameter of fibers were analyzed.Then,the statistical analysis of the factors affecting the durability and durability of FRP bars in aqueous solution,salt solution,acid solution,alkali solution,simulated seawater sand concrete solution,freeze-thaw cycles and coupling.(2)Based on the material properties of FRP bars and S-FRP bars,the design methods of flexural capacity of FRP bars and S-GFRP reinforced concrete beams under different failure modes are given.The minimum reinforcement ratio of FRP reinforced concrete beams is calculated by model method.The balance of reinforcement ratio was obtained by crushing the concrete in the compression zone while the FRP bar was broken.It was found that the minimum reinforcement ratio and the equilibrium reinforcement ratio were only related to the material properties of the FRP bars and concrete;considering the different concrete of the compression zone in the force stage,the calculation method of the creep stress of FRP bars in FRP reinforced concrete beams under elastic state and elastoplastic state is proposed.(3)The reinforced concrete sea sand concrete beam was used as the control group,and the GFRP bars and S-GFRP bars sea sand concrete beam were coupled in a concentration of 5% salt solution and 20%-25%,40%-45% stress level.The durability of 3 months was tested experimentally.The degradation law of seawater sea sand concrete beam is analyzed by failure mode,bearing capacity,mid-span deflection,crack distribution and development.The study found that after 3 months,the reinforced concrete sea sand concrete beam had slight corrosion,and the GFRP reinforced concrete beam had no obvious degradation,while the S-GFRP reinforced concrete beams are subjected to tensile failure of S-GFRPbars under 40%-45% stress level coupling.