Study On Mechanical Properties Of FRP Constrained High Performance Concrete Columns Under Axial Compression

With the rise of super high-rise buildings,long-span bridges and underground constructions,the performance requirements for the strength,durability,and workability of concrete structures have gradually increased.However,in actual projects,due to the adverse environmental impact(concrete freeze damage,Aging,etc.),concrete deterioration is inevitable,and the research of high-performance concrete has become one of the hot topics at present.The current research on the fiber reinforced composite material(FRP)confined high-strength concrete column has the problem of serious fragmentation after the FRP constrained column is damaged,and the damage of the specimen after the failure is in several parts.This paper aims at the problem of high damage degree of FRP-constrained high-strength concrete,and improves this problem by adding steel fiber.This paper first designs the mix ratio of high-strength self-compacting concrete,and designs the mix ratio of steel fiber high-strength self-compacting concrete based on this benchmark mix.Then,according to the perspective of FRP “boundary restraint” steel fiber “internal restraint”,the axial compression test of FRP restrained steel fiber high-strength self-compacting concrete column was carried out.The main conclusions are as follows:(1)According to the mixing ratio of high-strength self-compacting concrete,the mixing ratio of steel fiber high-strength self-compacting concrete is prepared.When the water-binder ratio under different steel fiber content is 0.3,its fluidity,filling property and intermittent passing performance of steel bar work performance meet the specification requirements.The basic mechanical parameters required for finite element simulation are obtained through the uniaxial tensile test of FRP sheet and the static compressive elastic modulus test of concrete.(2)From the perspective of FRP “boundary restraint” and steel fiber “internal restraint”,through the axial compression test results of FRP-constrained steel fiber high-strength concrete cylinders under different boundary constraints,the reinforcement effect of steel fibers on high-strength concrete cylinders is investigated.The test results show that with the increase of boundary confinement layers,the axial compression performance of concrete has been significantly improved.Compared with FRP "boundary confinement",steel fiber "internal confinement" is used as the reinforcing material of internal concrete,which is the secondary factor in the improvement effect of concrete axial compression performance.The "internal restraint" effect of steel fiber is mainly reflected in the improvement of the failure form of the high-strength concrete column.The damaged steel fiber concrete column almost maintains the shape of the complete column,which is convenient for the secondary reinforcement of the structure.In addition,the "internal restraint" effect of steel fibers can improve the ductility of concrete columns,improve the shortcomings of high-strength concrete brittleness,on the other hand,it can increase the strength of high-strength concrete columns to a certain extent.(3)Through the axial compression test results of the steel fiber high-strength self-compacting concrete cylinder confined by two-layer CFRP strips,the reinforcement effect of the steel fiber "internal confinement" on the concrete cylinder in the form of strip confinement is preliminarily investigated.The test results show that under the effect of steel fiber "internal restraint",the bearing capacity and ductility of the high-strength concrete column confined by two-layer CFRP strips have a certain increase compared with the unconfined column,but the lifting range is limited.It is mainly reflected in the improvement of the damage morphology.Like the fully-wrapped CFRP confined column,the steel fiber high-strength concrete column constrained by CFRP strips still maintains the shape of a complete column after failure.(4)Through the axial compression results of CFRP-constrained steel fiber high-strength self-compacting concrete square columns,under different boundary constraints,the reinforcement effect of steel fiber "internal constraints" on the concrete square columns was investigated.The test results show that,with the CFRP layers increases,the bearing performance of high-strength concrete square columns is significantly improved.Compared with plain high-strength concrete columns,the effects of "internal restraint" effect of steel in concrete square columns is better than the high-strength concrete column,indicating that the incorporation of steel fiber has a more significant lifting effect on the high-strength concrete square column.The load-displacement curve of the CFRP-constrained high-strength concrete square column shows a characteristic similar to a "yield platform",and the load increases slowly with the axial displacement.As the CFRP layers and the amount of steel fiber increase,the length of the "yield platform" section increases.(5)The axial compression test of FRP-constrained high-performance concrete is simulated by the ABAQUS finite element software.The simulation results are in good agreement with the test results,which provides a basis for the calculation of the bearing capacity of FRP-constrained high-performance concrete columns.By finite element simulation of the pressure test at different axial dimensions of FRP-constrained high-performance concrete.The simulation results show that there is almost no size effect on the compressive strength of CFRP-constrained high-strength concrete columns under different sizes.