Flexural Behavior Of T-Shaped UHPC Beams With Varying Longitudinal Reinforcement Ratios

Ultra-high Performance Concrete(UHPC)is a new generation of high-performance fiber reinforced cement-based composite material,which has the advantages of ultra-high strength,ultra-high toughness and ultra-high durability.It is applied to bridge deck structure in bridge engineering and can effectively reduce the cross-sectional height of the component,reduce the self-weight and prevent the bridge deck from cracking.In this thesis,the flexural performance of UHPC waffle deck slabs has studied from three aspects: static bending test,theoretical analysis of flexural bearing capacity and finite element simulation.Mainly completed the following work:(1)The basic mechanical properties of UHPC materials were tested,and the mechanical properties of UHPC under uniaxial compression and tensile load were determined respectively.The test results show that the compressive strength of UHPC is 160 MPa for cube and 136.6MPa for prism under compressive load.UHPC has a high tensile strength under tensile load,and has a strain hardening stage in the tensile process,and the ultimate tensile strength is 9MPa.(2)Using the principle of equivalent width,six full-length T-shaped beam models with different longitudinal reinforcement ratios were designed and made.On this basis,the bending resistance and failure mechanism of T-shaped UHPC beams were studied by static load tests.The results show that because UHPC has excellent tensile strength and tensile toughness,the ultimate flexural capacity and ductility of T-shaped UHPC beams will be reduced if the longitudinal reinforcement ratio is reduced,but the failure form of the beams will not be changed.In other words,the T-shaped UHPC beams still have the characteristics of ductility failure when the longitudinal reinforcement ratio is small or even zero.(3)Based on the section analysis and test results,the theoretical calculation formula of ultimate bending capacity of T-shaped section UHPC beams is derived,and the functional relationship between the reduction coefficient of tensile strength and longitudinal reinforcement ratio of UHPC beams has proposed.Based on nine T-shaped UHPC beams in the existing research,the applicability of the proposed formula for ultimate bending capacity of T-section UHPC beams was verified.The results show that the theoretical calculation formula proposed in this thesis has good applicability.(4)Based on the test results of material properties and related studies,the tensile and compressive constitutive models of UHPC were determined respectively.The finite element model of T-shaped UHPC beam is established by using ABAQUS finite element analysis software.The simulated load-deflection curve is in good agreement with the load-deflection curve obtained from the test,and the surface principal strain cloud image is close to the actual crack development.(5)Based on parameter analysis,the influence rules of UHPC compressive strength,tensile strength,tensile ductility,yield strength of tensile reinforcement and longitudinal reinforcement ratio on the flexural capacity of T-shaped UHPC beams are clarified.The results of parameter analysis show that the main parameters affecting the flexural capacity of T-shaped UHPC beams are UHPC tensile strength,yield strength of tensile reinforcement and longitudinal reinforcement ratio,and UHPC ductility mainly affects the early stiffness of Tshaped beams.