Experimental Study And Numerical Analysis Of Flexural Behavior Of Concrete Beams With Mixed Reinforcement

The corrosion of steel reinforcement has always been an important factor affecting the bearing capacity and durability of the structure.Governments of various countries spend more and more money on the corrosion prevention of the components every year,but it still cannot fundamentally solve the problem of the shortening of the life of the components caused by the corrosion of steel reinforcement.The emergence of FRP bars has brought about a way to solve the corrosion of steel bars once and for all and a higher cost performance.FRP bars themselves are not corroded in high temperature,humidity,chloride ion and other environments,and FRP bars have excellent mechanical properties,the bearing capacity of FRP bars is much greater than ordinary steel bars,Therefore,the application of FRP bars in practical engineering can not only meet the needs of preventing steel corrosion,but also effectively improve the bearing capacity of components.But the mechanical properties of FRP bars themselves determine that FRP bars are prone to brittle failure,which is not directly applicable to engineering.So,it is very important to compare the test performance of different kinds of FRP bars and find a way to make FRP bars have longer life.Therefore,this paper uses different kinds of FRP bars to carry out flexural tests.At the same time,we use the finite element software to study the mechanical properties of hybrid reinforced beams.In this paper,the properties of different kinds of FRP reinforced concrete beams and mixed reinforced concrete beams are studied as the objective,7 FRP reinforced concrete beams are tested by bending,and 5 mixed reinforced concrete beams are simulated by finite element method.The specific contents are as follows:(1)Due to the mechanical properties of FRP bars produced by different manufacturers have great differences,so the test selected different kinds of FRP bars,and the tensile test of FRP bars,the mechanical properties of different kinds of FRP bars and damage patterns,the definition of the constitutive relationship model of FRP bars.(2)The bending test of 7 FRP bars concrete beams is carried out to study the failure patterns of different kinds of FRP bars.The test results show that: for the FRP bars concrete beams,the assumption of flat section is still applicable;There is enough friction between the FRP bars and concrete with sand surface,so they can work together.Therefore,the test beam will produce multiple cracks when it is damaged,which can play a good role in energy dissipation.The load-deflection curve of FRP reinforced concrete beam is basically divided into two stages.The types of reinforcement and FRP bars of the test beam will affect the slope of the curve,but the load-deflection curve is basically a double straight line.There is not enough bonding force between FRP bars and concrete when the test beam of FRP bars is damaged,which leads to the bonding and sliding failure of the test beam,so it is not suitable to be used as tensile bars directly.(3)The finite element software ABAQUS is used to simulate the FRP reinforced concrete beam,and the failure form,bearing capacity and load deflection curve of the FRP reinforced concrete beam are obtained.The comparison and analysis with the test results verify the correctness of the model.After that,by adjusting different material parameters of the finite element model,the factors that may affect the deformation of the FRP reinforced concrete beam are modeled and analyzed.The results show that the beam section height,the type of FRP bars The reinforcement ratio of FRP bars has a greater impact on the deflection of FRP reinforced beams,while the concrete strength and loading method have a smaller impact on the deflection of FRP reinforced concrete beams.In order to meet the deflection requirements of FRP reinforced beams under normal service conditions,we can comprehensively consider ways such as increasing the beam section,adjusting the types and reinforcement ratio of FRP bars,or applying prestressed bars and reverse cambering.(4)The finite element software ABAQUS was used to test and simulate the concrete beams with mixed FRP bars and steel bars.The load-deflection curve of the beams with mixed reinforcement,the failure process of the beams with suitable reinforcement,the cracking load and ultimate load of the beams with mixed reinforcement were obtained.The results show that: The failure process of hybrid reinforced beams is similar to that of ordinary reinforced concrete beams,which shows three distinct stages: the uncracked concrete stage,the crack of concrete to the yield stage of tensile reinforcement,and the yield stage of tensile reinforcement to the failure stage of concrete beams.The load-deflection curve of the hybrid reinforced beam is located between the ordinary reinforced concrete beam and the pure FRP reinforced concrete beam,the ductility performance is better than that of the pure FRP reinforced concrete beam,and with the increase of the reinforcement rate,the load-deflection curve is more inclined to the ordinary reinforced concrete beam;The cracking moment of the test beam with different reinforcement ratio is basically the same.The cracking moment has nothing to do with the proportion of FRP bars and rebar,but only has something to do with the section size of the test beam and the tensile strength of concrete.The cracking moment of a hybrid reinforced beam can be obtained by calculating the gross moment of inertia.The ultimate bearing capacity of hybrid reinforced beams is greater than that of pure FRP reinforced concrete beams,but smaller than that of ordinary reinforced concrete beams,indicating that ordinary reinforcement can play a greater role than FRP bars when the test beam is damaged.In the case that the component size is the same and only the types of FRP bars are different,the bearing capacity of the FRP bars with large elastic modulus is greater,and the deflection deformation is smaller under the same load conditions.Therefore,in the actual project,the FRP bars with larger elastic modulus should be selected as the tension bars as far as possible.