Study On Shear Behavior Of Prestressed UHPC Beam

Ultra-high performance concrete(UHPC)is a new type of water conservancy matrix composite.Compared with ordinary concrete,it has many excellent properties,such as ultra-high strength,high toughness,small creep,good durability and so on.At present,UHPC materials are widely used in civil engineering.There are about 400 UHPC bridges built all over the world.Perfecting the design theory and method of UHPC structure is the prerequisite to popularize the appli cation of UHPC engineering,and the research on shear capacity of reinforced concrete structure is one of the key points in the design of concrete structure.Because there are many factors affecting shear failure and the study of shear mechanism is not eno ugh,the shear bearing capacity has not set up a complete theoretical system at present.In order to facilitate the engineering application of shear design,most of the countries adopt empirical formula as the design basis.Because the code is an empirical formula based on the experimental data of ordinary concrete beams,it is not fully applicable to the calculation of shear capacity of reinforced UHPC beams.Therefore,the study of shear capacity of UHPC members needs to be continuously studied.It is of great significance to provide the corresponding design parameters and calculation theory for the engineering application of bridge design by studying the shear resistance of UHPC.In order to study the shear behavior of prestressed UHPC beams,the shear tests of three prestressed UHPC beams have been designed in this paper.Combined with the experimental results,the modified pressure field theory and the finite element model are used to study the experimental beam.The main work is as follows:(1)on the basis of the shear test of three test beams,the load is recorded separately.Based on the data of displacement and strain,the mechanical properties,crack distribution,failure form and web stress state of the test beam are analyzed.The shear-span ratio is the main parameter of the test beam.(2)based on the modified pressure field theory(MCFT),the constitutive relation of UHPC under pure bending condition is modified,and the analytical model of shear capacity of UHPC beam under bending-shear composite action is established.The experimental results are in good agreement with the calculated r esults,which indicates that the MCFT theory can be used to calculate the shear capacity of UHPC members.(3)the finite element model of prestressed UHPC beam is established based on ABAQUS software,and several factors affecting shear resistance are ana lyzed.The tensile stress,longitudinal reinforcement ratio and stirrups ratio are mainly studied.Effects of pre-stressed tendons and UHPC tensile strength on shear properties of test beams.(4)on the basis of shear theory and other experimental data of UHPC beam,considering the factors of shear span ratio,stirrups ratio,prestress and UHPC strength,the proposed formula of shear bearing capacity is put forward,which can be used as a reference for the design of UHPC shear strength in practical engineer ing.