Study On Mechanical Properties Of Reinforced Concrete Beams Strengthened With BFRP

In recent years,due to the frequent occurrence of structural damage,bearing capacity reduction and durability decline in the long-term use of concrete structures,the reinforcement technology of concrete structures has become the focus of research in the field of civil engineering in China.Basalt fiber reinforced polymer(BFRP)is a new type of light weight,high strength and corrosion resistant material.It is widely used in civil engineering structures and components,especially in reinforced concrete structures.Based on the bending tests and ABAQUS finite element analysis of four reinforced concrete beams strengthened with basalt fiber grids and basalt fiber reinforcements with different degrees of damage and one ordinary reinforced concrete beam,the failure modes and bending properties of reinforced concrete beams strengthened with different degrees of damage by different FRP materials are studied.The main work is as follows:(1)The mechanical properties of basalt fiber grids were tested,and the tensile strength and elongation at break were measured,which provided basic data for finite element simulation analysis.(2)Four reinforced specimens and one common specimens were tested.The phenomenons show that the failure modes of the specimens are basically similar.All the specimens are yielded by the tensile steel bars of the beams,and the concrete in the compression zone is crushed.(3)Comparing and analyzing the test results of five specimens,it is found that:?Two kinds of BFRP materials can effectively reduce the mid-span displacement of reinforced concrete beams in failure stage,and the reduction of mid-span displacement is more significant in yielding stage and failure stage under non-damage state.? Both kinds of BFRP materials can effectively improve the bearing capacity of reinforced concrete beams,but the surface embedded basalt fiber reinforcement(BFRP)can improve the bearing capacity more significantly;and the strengthening effect is more obvious under the condition of non-damage;? both the surface embedded BFRP and the external basalt fiber grille(BFG)have no obvious influence on the ductility of specimens;? Whether the specimens are damaged before reinforcement or not,the effect of BFRP on restraining the strain growth of steel bar is better than that of BFG.(4)The failure modes and the overall trend of load-displacement curves of the finite element simulation specimens are in good agreement with the experimental results,which verifies the correctness of the constitutive relationship and the established model.On this basis,the extended parameter analysis is carried out.The strength grade of concrete has no significant effect on the bending performance of reinforced specimens;the bending capacity of reinforced beams decreases with the increase of damage degree;the bending stiffness of reinforced beams increases with the increase of reinforcement ratio,and the bending capacity decreases with the increase of reinforcement ratio.(5)By studying the stress of reinforced concrete beams in the cracking,yielding and ultimate stages,the calculation methods of bending moment eigenvalues in each stage are given.Based on the experimental study and the formulas for calculating the bending capacity of reinforced bending components in current codes,considering the strain lag effect caused by secondary loading,the proposed formula for calculating the bending capacity of damaged concrete beams strengthened with FRP is given,which provides a theoretical basis for the design of damaged concrete structures strengthened with FRP materials.