Study On Flexural And Seismic Behavior Of Concrete Shear Wall Reinforced With CFRP Grids

The traditional reinforced concrete shear wall will suffer great damage and destruction under the action of moderate and large earthquakes and produce large residual deformation,resulting in a difficult and costly post-earthquake repair process.Studies have shown that the reasonable application of fiber reinforced polymer(FRP)in shear walls can effectively reduce the damage to them and improve the load-carrying capacity and repairability of specimens.As a novel form of FRP,carbon fiber reinforced polymer(CFRP)grid has the characteristics of bidirectional loading,good integrity,crack control and excellent anchoring performance,etc.In recent years,it has been applied and studied in new structures and showed good results.However,the corresponding application in shear wall structures and research is scarce.In this paper,the flexural and seismic behavior of the concrete shear walls with CFRP grids are systematically studied by means of experimental research,theoretical analysis and numerical simulation.The main research contents and results are as follows:(1)Though reversed cyclic loading tests on five concrete shear wall with CFRP grids and one reinforced concrete shear wall,the influences of different reinforcement configuration and the hybrid proportion of steel and CFRP grids on the flexural and seismic behavior of shear walls were investigated.The hysteretic behavior,stiffness characteristic,ductility,strength degradation,energy dissipation capacity,residual deformation and reinforcement strain of shear walls were analyzed comprehensively.The results showed that the hysteresis curves of shear walls with CFRP grids presented obvious secondary stiffness.The load-carrying capacity increased significantly and the residual deformation decreased evidently.The shear wall with CFRP grids placed as exterior layers exhibited more effective suppression of crack development and superior load-carrying capacity.However,the arrangement of CFRP grids in the middle of the wall was more conducive to maintaining the basic stability of the load-carrying capacity of the members,and the residual deformation was smaller.As the proportion of CFRP grids increased,the shear wall exhibited better crack control effect,greater secondary stiffness,higher load-carrying capacity and smaller residual deformation after concrete crushing,but the ductility of specimen decreased.There is an optimal value for the hybrid proportion that maximizes the energy dissipation of shear walls.When the hybrid proportion is about 1:1,the energy dissipation capacity was the same as that of reinforced concrete shear walls.Therefore,the concrete shear wall with CFRP grids arranged as exterior layers and steel bars arranged in the middle has the most ideal seismic behavior.(2)The strain of the vertical CFRP grids at the bottom of the wall was approximately linear along the section,indicating that the plane section assumption is basically true.The peak strain of the vertical CFRP grid at the edge was in the range of 0.011-0.014,and the strength utilization rate was about 65-75%.Based on the ductile failure criterion of "the outermost tensile steel bar yield-the edge concrete crushing-the outermost vertical CFRP grid bar rupture",the calculation formula of flexural capacity of concrete shear wall with CFRP grids was derived.The ultimate compressive strain of the concrete at the edge of the compression zone was calculated iteratively using the strain data of the CFRP grids tested.The calculated loadcarrying capacity was in good agreement with the test results,and the ultimate compressive strain of the concrete was recommended to be 0.006 in the design.(3)The finite element analysis model of shear wall with CFRP grids based on MTVLEM could well reflect the changing characteristics of the load-displacement relationship of specimens from yield to failure,but it underestimated the energy dissipation of shear wall specimens.The simulated results of specimen load-carrying capacity were close to the test results,with an average error of less than 3%.The average error of peak displacement simulation results was less than 1%,but the simulation accuracy was not stable.The finite element analysis model was used to parameterize the shear wall specimens with different axial compression ratios and shear span ratios.The simulation results were close to the theoretical calculation results with an average error of less than 10%.Increasing the axial compression ratio or decreasing the shear span ratio within a certain range would increase the load-carrying capacity of shear wall specimens,which was basically consistent with the variation rule of traditional reinforced concrete shear wall.