Study On The Shearing Behaviors Of Ultra-high Performance Concrete With Damage

As one of the most excellent new cementitious composite materials in recent years,Ultra High Performance Concrete（UHPC）is widely used in the field of civil engineering due to its excellent material properties.However,because the mechanical properties of UHPC are very different from traditional concrete,there are still great deficiencies in the research on the mechanical properties of UHPC materials and the theoretical design of components.At present,domestic and foreign scholars have carried out a lot of experimental research and theoretical analysis on the constitutive relationship of UHPC materials and the shear performance of components,but it is still far from obtaining a common understanding.Based on the UHPC constitutive relationship proposed by our research based on meso-damage mechanics,this paper explores the shear resistance of the oblique section of UHPC beams.The main research work and conclusions are as follows:（1）It is verified that the UHPC damage constitutive model proposed by our team is feasible for the study of shear behavior of UHPC beams.（2）Based on the test beam parameters in the literature,a finite element model was established,and the test results were compared and analyzed.Research shows that the finite element simulation results are close to the test results,which can reflect the shear performance of UHPC beams.The shear span ratio determines the failure mode of the beam when shear failure occurs.Thanks to the excellent mechanical properties of UHPC materials,UHPC beams still show a certain degree of ductility the diagonal tension failure that occur under larger shear span ratios.Critical oblique cracks don’t form very soon.（3）Parametric analysis on the factors affecting the shear performance of UHPC beams was carried out.Studies showed that the shear span ratio,reinforcement ratio,and stirrup ratio had an important influence on its shearing performance.The shear span ratio has the most significant effect on the shearing resistance.When the shear span ratio was increased from2.0 to 2.5 and 2.8,the shear capacity was reduced by 18.91% and 24.26% respectively.The increase in reinforcement ratio and stirrup ratio will result in a smaller increase in shear capacity.Increasing the reinforcement ratio can effectively improve the anchoring effect of the longitudinal reinforcement,thereby increasing the shearing resistance.Increasing the hooping ratio can improve the ductility of the beam,increase the shear strength,and make the component failure shape good.（4）The shearing resistance formula for UHPC members proposed by domestic and foreign codes was compared and analyzed,and it was found that the current codes are conservative and have greater dispersion in estimating shearing resistance of UHPC members.This formula takes into account the quantitative relationship of the oblique fracture inclination angle.Based on the damage constitutive relation of UHPC proposed by our team,the shear capacity calculation formula of UHPC member is proposed Based on this formula,the mean value,standard deviation,and coefficient of variation of the ratio between the calculated result and the test result are 1.00,0.06,and 0.06 respectively.The calculation method proposed in this paper is more accurate and less discrete.