Shear Behavior Of Ultra High Performance Concrete Beam At Ambient Temperature

Ultra high performance concrete(UHPC)is a kind of new building material with ultra-high strength,high toughness and excellent durability.UHPC matrix with high-strength reinforcement can give full play to the material properties of UHPC.For the bearing capacity of the inclined section of UHPC beam,the cohesion of UHPC aggregate is small,but the bridging effect of fiber restricts the generation and development of inclined cracks.Due to the complex shear transfer mechanism,the research on the bearing capacity of the inclined section of UHPC beam is less;the bearing failure of the inclined section is brittle failure,and the safety prevention and control performance is poor.In view of this,this paper studies the bearing capacity of UHPC beams at room temperature,and the main work is as follows:(1)Adoption The UHPC was prepared by using river sand instead of quartz sand in the ternary cementitious material system of "cement silica fume mineral powder".The effects of standard curing,dry heat curing,steam curing and hot water curing on the mechanical properties of UHPC were studied.The test results showed that the effects of curing system on the compressive strength were: dry heat curing,steam curing,hot water curing,standard curing;dry heat curing The compressive strength of the cured cube increased with the increase of temperature.The compressive strength of 150 oC cube increased by 21.2% compared with 90 oC cube,and decreased by 8.9% in 7d-28 d age.The axial tensile strength of UHPC was greatly affected by the curing system.The dry heat curing at 150 oC increased by 33.4% compared with the standard curing.The higher the dry heat curing temperature,the greater the tensile strength;The water binder ratio is the key factor to affect the tensile strength.When the water binder ratio decreases from 0.22 to 0.18,the tensile strength increases by 24%.(2)The shear capacity tests of three UHPC simply supported beams were carried out at room temperature.The load displacement curves,strain changes of stirrups and longitudinal bars,crack distribution and development,shear capacity and other data were obtained.The influence of shear span ratio on shear capacity of UHPC beams was revealed.The test results show that the shear capacity of UHPC beam is greatly affected by the shear span ratio,and the test beam presents shear compression failure in the range of shear span ratio of 1.5 ~ 3.5;compared with the ordinary concrete beam,the non web reinforced UHPC beam does not appear cable-stayed failure in the larger shear span ratio,and the shear failure has a certain ductility;the shear capacity and ductility coefficient of UHPC beam are higher than the ordinary concrete.(3)A refined finite element model for shear performance analysis of UHPC beams is established,which is verified by the test results.The influence of shear span ratio,stirrup ratio,stirrup form,longitudinal reinforcement ratio and section size on the shear performance of UHPC beams is studied by expanding the range of parameters.The analysis shows that the shear span ratio,stirrup ratio and section size are the key factors affecting the shear performance,and the longitudinal reinforcement ratio has little influence on the shear performance of UHPC beams;the shear span ratio of UHPC beams without web reinforcement increases from 1.1 to 1.5,2.5 and 3.5,and the shear performance of UHPC beams with no web reinforcement increases from 1.1 to 1.5,2.5 and 3.5 The bearing capacity decreased by 22.2%,42.7% and 55.2% respectively,and the shear strength decreased with the increase of shear span ratio,and the decreasing range was gradually reduced;the shear strength increased with the increase of stirrup ratio,the larger the shear span ratio,the smaller the influence of stirrup ratio on the ultimate shear capacity;when the difference of reinforcement ratio was small,the reinforcement of a single reinforcement could not make up for the reinforcement pin bolt caused by the decrease of reinforcement quantity The reduction of application results in the reduction of ultimate shear capacity;the ultimate shear capacity increases with the increase of section size,and the larger section size will seriously reduce the shear ductility of UHPC beams.The section size increases from 200 mm×300 mm to 400 mm×500 mm,the shear capacity increases by 2.4 times,and the failure deflection decreases by 45%.(4)The influences of shear span ratio,longitudinal reinforcement ratio,stirrup ratio,steel fiber characteristics,section size and other factors on the shear performance of UHPC beams are systematically analyzed.By comparing the calculation methods of shear capacity of UHPC beams at home and abroad,the calculation methods of shear capacity of UHPC beams are developed.It has been verified by experiments that the multi parameter shear bearing capacity calculation method has good applicability and can provide theoretical support for the application of UHPC beam engineering.