Study On Constitutive Models Of Steel Fiber Reinforced Concrete With Two-graded Aggregate Under Uniaxial Compression And Tension

Steel fiber reinforced concrete with two-graded aggregate has the advantages of reducing cement consumption,reducing the temperature rise of insulation and reducing shrinkage.Therefore,it is widely used in hydraulic concrete structure,but its toughness and crack resistance is poor,which is limited in practical application.The random distribution of steel fiber can effectively improve the toughness and crack resistance of concrete.Therefore,it is of great significance to study the steel fiber reinforced concrete with two-graded aggregate,especially the research on constitutive models under uniaxial compression and tension can provide theoretical reference for the application of steel fiber reinforced concrete with two-graded aggregate in structural engineering.At present,the research on the two-graded aggregate concrete at home and abroad shows that the maximum size of coarse aggregate has no obvious influence on the compressive strength,tensile strength and tensile toughness of concrete,but the influence on the compressive toughness is not obvious.Therefore,when the length of steel fiber is 60mm,the uniaxial compression test of steel fiber reinforced concrete with two-graded aggregate is carried out,and the influence of the maximum size of coarse aggregate on compression toughness is studied.A statistical damage constitutive model under uniaxial compression and a modified smeared crack constitutive model under uniaxial tension which can consider the reinforcement of new steel fiber are established.The main contents include:(1)The uniaxial compression test of steel fiber reinforced concrete with twograded aggregate was carried out(5d end hook type steel fiber),and the axial compression stress-strain curves under different volume ratio of steel fiber were obtained.The influence of the maximum size of coarse aggregate on the compression toughness of concrete was studied,and the influence of volume ratio of steel fiber on Poisson’s ratio,compressive strength,peak strain and toughness(compression work,axial compression toughness ratio)was discussed.The results show that:the maximum size of coarse aggregate has no obvious effect on the stress-strain curve of concrete under axial compression;after steel fiber is added,the Poisson’s ratio and compressive strength of concrete increase slightly but not obviously,the peak strain and toughness increase significantly.It is recommended that Poisson’s ratio can be taken as 0.22 directly in practical application.(2)The statistical damage constitutive model of steel fiber reinforced concrete with two-graded aggregate under uniaxial compression is established.According to the statistical damage theory,the strain threshold and damage correction coefficient are introduced into the model,and the influence of fiber factor can be considered.The influence of the selection of elastic modulus(secant modulus and initial tangent modulus)on the accuracy of the model and the influence of steel fiber volume ratio on the model parameters and damage evolution rate are discussed.The results show that:the accuracy of the model is high,and it is recommended to use the initial tangent modulus and small strain threshold to study.Under the initial tangent modulus,the damage threshold is 0.3 times of the peak strain,and the damage correction coefficient is 0.99;when the volume fraction of steel fiber is 1.50%,the shape parameter of the model is reduced by 43%,the scale parameter is increased by 9%,the damage variable at 0.004 strain is 0.75,and the damage evolution rate is reduced by 16%.(3)A modified smeared crack constitutive model of steel fiber reinforced concrete with two-graded aggregate under uniaxial tension is established,which can reflect the effects of different steel fiber types,volume ratio,length and diameter.Based on the strain strengthening plastic model,the damage plastic parameters are calibrated,and the constitutive relationship of ordinary concrete is determined.According to the two-phase composite law and bond-slip model,different types,volume ratio and size of steel fibers are introduced into the elastic stage and post crack stage of concrete.The accuracy of the model is verified by the secondary development of UMAT subroutine interface provided by ABAQUS.(4)The uniaxial tensile simulation of steel fiber reinforced concrete with twograded aggregate is carried out,and the stress-strain curve is predicted.The effects of steel fiber type(straight,3D,4D,5D end hook type)and volume ratio(0.50%,0.75%,1.00%,1.25%,1.50%)on the tensile strength,peak strain and toughness(tensile work,axial tensile toughness ratio)of steel fiber reinforced concrete are discussed.The results show that:the strengthening and toughening effect of 1.50%volume fraction of straight steel fiber is almost the same as that of 1.00%volume fraction of 3D end hook,0.75%volume fraction of 4D end hook and 0.50%volume fraction of 5D end hook.It is suggested that 5D end hook steel fiber with volume ratio of 0.50%should be selected in practical engineering.