Experimental Study On In-plane Compressive And Shear Properties Of Concrete Slab Reinforced With Cfrp Grid

Carbon fiber composite materials are widely applied and researched in civil engineering.As a new type of product form,carbon fiber grid has been widely concerned.For wall-type concrete members in structure,the reinforcement is usually arranged in the form of an orthogonal grid.The carbon fiber grid is the monolithic and rigid product which is made by immersing the carbon fiber in corrosion resistant resin.Compared with the steel grid,there are many good overall performances with carbon fiber grid,such as effective construction,lightweight,high tensile strength,corrosionresistance,corrosion resistance.Therefore,it is of theoretical and practical value to study the shear mechanical properties of wall-type concrete members reinforced with carbon fiber grid when they work together.In this paper,the in-plane compression and shear mechanical properties of six concrete test slabs,including five concrete slabs reinforced with carbon fiber grid and one concrete slab reinforced with steel grid,were studied from three aspects: theoretical analysis,experimental research and programming.Firstly,in order to achieve the in-plane compression-shear loading scheme,the orthogonal grid was placed diagonally in the concrete with the angle of 45.Then the two vertical sides of the slab were compressed by four point on each side,and the two horizontal sides of the slab were pulled by four point on each side.In terms of the medium main region,it could be suffered the pure shear force or compression-shear force.According to the results of test,it was found that under the in-plane compressive and shear force or pure shear force,the main failure mode of test slabs was that the concrete between cracks in the compression shear(or pure shear)area was crushed,and then the test slabs failed.Then,according to the analysis of test data,this paper studied the effect of compression-shear ratio and reinforcement ratio on the shear performance of concrete slabs reinforced with carbon fiber grid,as well as the feature of the shear stress and shear strain curve.It was found that the greater the absolute value of the compression-shear ratio,the greater the shear capacity of the test slab.When the compression-shear ratio was-0.2,the shear capacity of the test panel was increased by about 5%.When the compression-shear ratio was-0.5,the shear capacity of the test panel was increased by about 18%.The greater the reinforcement ratio,the greater the shear capacity of the test slab.When the reinforcement ratio increased from 0.84% to 1.96%,the shear capacity of the test panel increased by about 23%.The shear stress and shear strain curve of concrete slabs reinforced with carbon fiber grid could be divided into two stages: the elastic stage before concrete cracking and the elastic stage after concrete cracking,which lacked the plastic stage compared with that of the concrete slab reinforced with steel grid.The main reason for this phenomenon was that the carbon fiber grid was linear elastic materials without the yield stage.Last,it was found that the degree of "softening",namely the degree of reduction of compressive bearing capacity of the concrete between cracks,of the concrete of the concrete slab reinforced with carbon fiber grid was greater than that of the concrete slab reinforced with steel grid.Based on this finding,this paper fitted the test data with exponential and modified the denominator constant term in the expression of the softening coefficient of the concrete compressive average stress-average strain expression in the rotating angle softened truss model(RA-STM).Thus,a variable-angle softened truss for the concrete slab reinforced with carbon fiber grid was proposed.and was calculated by MATLAB program.Compared the calculated value of the shear capacity with the test value of the shear capacity,it was found that the calculated value and the test value were in good agreement.And the coefficient of variation was only 0.034.It showed that the variable angle softened truss model for the concrete slab reinforced with carbon fiber grid proposed in this paper had good predictability.Then the MATLAB calculation program of the model was used to analyze the effect of concrete strength grade on the in-plane shear performance of the concrete slab reinforced with carbon fiber grid.The results showed that the higher the concrete strength level,the higher the shear capacity of the slab and the higher the deformability of the slab.The strength of concrete increased from 24.6MPa to 32.5MPa,and the shear bearing capacity of the slab increased by 25%.