Study On Mechanical Behavior And Application Of Steel-Ultra-High Performance Concrete Composite Box Girder Deck System

This dissertation investigates the mechanical behavior of the steel-ultra-high performance concrete(UHPC)composite box girder deck system.Theoretical analysis,experimental research and numerical simulation were conducted.Design methods and optimization suggestions were proposed.The main results and achievements of the research are as follows:(1)The force and deformation in the process of axial tension of UHPC were measured accurately by using the optimized dog-bone axial tensile test method.Based on the test,the uniaxial tensile constitutive model of UHPC suitable for different steel fiber content was proposed.Through the axial compressive test,the influence of steel fiber content and curing method on the compressive properties of UHPC was studied.Based on the comparison of the existing literature results and specifications,suggestion was proposed for the uniaxial compressive constitutive model of UHPC,and unknown parameters were calibrated.(2)11 UHPC slabs and 1 ordinary concrete(C50)slab tests were designed and completed,with static midspan single-point loading.The effects of slab thickness,cover thickness,reinforcement ratio,loading area and concrete type on punching shear and bending performance of the test slabs were studied.The failure mode,bearing capacity and strain distribution of the test slabs were obtained.The stress and deformation characteristics of different failure modes were analyzed.(3)The mechanism of punching shear failure of UHPC slab was analyzed.With the plastic limit analysis,the punching shear failure mechanical model of UHPC slab is established,and the semi-theoretical and semi-empirical calculation formula of punching shear capacity was put forward.Based on the bending failure mechanism,the theoretical calculation formula of bending capacity was proposed.The one-dimensional fiber model considering the whole process of bending failure of UHPC slab was established,and the accuracy of bending capacity calculation of the model was verified based on the test results.Through the analysis of the bearing capacity parameters,the design suggestions of UHPC bridge deck were proposed.(4)Steel-UHPC composite box girder tests were designed and completed.The development law of deformation and strain of the composite box girder under elastic conditions and the bearing capacity,deformation and crack under plastic condition were analyzed.The failure characteristics of the composite box girder with different thickness of UHPC slab were revealed.The elastic analysis model of composite box girder was established,which can consider the shear lag,interfacial slip and shear deformation of steel web simultaneously,and the analytical solution is derived.(5)The fine finite element model of steel-UHPC composite box girder deck system was established,and the local mechanical performance analysis was carried out.The key parameters,such as the thickness of the bridge deck,the spacing between diaphragms and the spacing between small longitudinal beams,were optimized.And the design suggestions for the steel-UHPC composite box girder deck system were proposed.