Research On Bearing Capacity Of Inclined Section Of Ultra High Performance Concrete Beams Without Web Reinforcement Under Fire

Ultra high performance concrete（UHPC）has the characteristics of ultra-high strength,high ductility and low permeability,which is widely used in the field of civil engineering.Compared with ordinary concrete and high-strength concrete,UHPC has less internal voids and micro cracks,compact microstructure and low permeability.Therefore,high temperature has more severe effect on the reduction of inclined section bearing capacity of UHPC beam.At present,there is no systematic report on the bearing capacity of UHPC beams under fire.Based on the test results,the refined finite element model of UHPC beam under fire is established for parameter analysis.The main research contents are as follows:（1）The experimental study on the bearing capacity of UHPC simply supported beams without web reinforcement was carried out under eight conditions.The influence of longitudinal reinforcement ratio and shear span ratio on the bearing capacity of the test beam was investigated.The shear bearing capacity,stress-strain law,load displacement curve,crack distribution and development of the test beam are obtained,and the damage evolution process and failure mechanism of the test beam are explored.The results show that the longitudinal reinforcement ratio and shear span ratio are the key factors affecting the bearing capacity of UHPC beams without web reinforcement at room temperature.The larger the shear span ratio is,the more dangerous it is for the test beams.When the longitudinal reinforcement ratio is 6.2%,the inclined section bearing capacity of the test beam is the best.（2）The experimental study on the bearing capacity and residual shear capacity of UHPC simply supported beams without web reinforcement under six conditions of ISO834 fire was carried out.The effects of temperature field,longitudinal reinforcement ratio,shear span ratio and load level on the failure mechanism and damage evolution of the inclined section of the test beam under fire were investigated.The temperature field distribution and load displacement curve of the test beam,the bursting and crack development of the shear compression zone and the residual value of the shear capacity of the test beam under fire are obtained.The results show that the failure ductility of UHPC beams under fire is better than that under normal temperature.Shear span ratio and load level are important factors affecting the fire resistance of UHPC beams without web reinforcement.The fire resistance of the beam decreases with the increase of shear span ratio and load level.The results show that the spalling seriously reduces the bearing capacity of the test beam.（3）The thermal mechanical coupling refined finite element model is established by using ABAQUS,and the extended parameter analysis is carried out to study the influence of load level and shear span ratio on the failure mechanism of inclined section under fire.The results show that the fire resistance of UHPC beam decreases significantly with the increase of load level.The fire resistance of UHPC beams decreases with the increase of shear span ratio.（4）The thermal mechanical coupling refined finite element model is established by using ABAQUS,and the extended parameter analysis is carried out to study the influence of load level and shear span ratio on the failure mechanism of inclined section under fire.The results show that the fire resistance of UHPC beam decreases significantly with the increase of load level.The fire resistance of UHPC beams decreases with the increase of shear span ratio.Based on the comprehensive analysis of the influence of various parameters on the failure mechanism of the inclined section of UHPC beams without web reinforcement under fire,the fire resistance design suggestions and high temperature burst prevention and control measures of the inclined section of UHPC beams are put forward.