Calculation Method Of Shear Capacity Of R-UHPC Beam Based On Variable-Angle Truss Model

The shear behavior of ultra-high performance concrete(UHPC)beams is a hot research topic due to many influencing factors and calculation theories.The shear capacity of reinforced ultra-high performance concrete(R-UHPC)beams is calculated by truss model,and the axial angle between the truss strut and the beam is fixed,so the calculation results are inaccurate.Therefore,this paper combines the shear failure test of six R-UHPC beams,verifies the finite element model according to the test,and obtains the variation law of the axial angle between the truss diagonal compression bar and the beam through the finite element parameter analysis,and puts forward the calculation method of shear capacity based on the variable angle truss model.At the same time,330 R-UHPC shear test beams at home and abroad were collected,and the contribution of different influence parameters to the shear capacity of RUHPC beams was systematically analyzed.The calculation method of shear capacity in multi-national codes is introduced,and the calculated value of shear capacity is compared with the database test value.The main contents and conclusions are as follows:(1)The load deflection curve,load strain curve and crack distribution of six test beams were verified by finite element analysis.Combined with the verified finite element model,the main influence parameters were analyzed.The results show that the increase of UHPC compressive strength can significantly improve the ultimate load of the beam;With the increase of UHPC tensile strength,the cracking load and ultimate load increase approximately linearly,and the increase of cracking load is approximately equal to the increase of tensile strength;The greater the stirrup ratio is,the greater the stiffness and ultimate load of the beam are,and the yield strength of the stirrup increases,which improves the deformation capacity of the beam.(2)The shear span ratio is the main factor affecting the shear capacity of R-UHPC beams,and the UHPC steel fiber content and stirrup ratio are also important factors affecting the shear capacity;The shear capacity of R-UHPC beams with steel fiber content of 0.5%and more than 1%is significantly different.After the parameter expansion analysis of the test beam,the dip angle of the main inclined crack ranges from 33° to 53°;The shear span ratio is the main influence on the inclination of the main inclined crack,followed by the stirrup ratio and steel fiber content.With the increase of shear span ratio,the inclination of main inclined crack of most R-UHPC beams decreases first and then increases;The dip angle of main inclined fracture increases with the increase of stirrup ratio;When the shear span ratio is above 1.6,the inclination angle of the main inclined crack decreases with the increase of steel fiber content.(3)330 R-UHPC shear test beams were collected,and the main parameters affecting the shear performance of beams were analyzed.The results show that the increase of UHPC compressive strength can make the neutral axis of the beam section move down,make the concrete in the shear compression zone play more shear resistance role,and increase the arch effect of R-UHPC beam.The R-UHPC beam with small shear span ratio is greatly affected by the arch,and the beam with large shear span ratio is greatly affected by the truss composed of stirrups.(4)The calculation results of shear capacity of R-UHPC beams in Chinese concrete and Bridge codes are too conservative.The prediction effect of French code for beams with web reinforcement is better,and the calculation of beams without web reinforcement is conservative.The prediction effect of Japanese code for beams with and without web reinforcement is similar,but it is conservative on the whole.The calculation results of Korean code and Swiss code are conservative,and the prediction effect of beams with web reinforcement is better than that of beams without web reinforcement.Based on the calculation method of variable angle truss model,the calculated value is close to the experimental value,which can better predict the shear capacity of R-UHPC beam.