Research On Concrete Structural Layer Flexural Static And Fatigue Mechanism Of Orthotropic Steel-High Performance Concrete Composite Bridge Deck

Orthotropic steel bridge deck is the first choice for long-span steel bridge because of its convenience for construction,wide application and lightweight high strength.However,the development and promotion of orthotropic steel bridge deck restricted by two factors which are fatigue cracking of welding details and bridge deck overlays damage.Using shear connectors to form orthotropic steel-ultra high performance concrete(UHPC)composite bridge deck is expected to solve these problem.The fatigue model changes with the introduction of UHPC layer.Thus,the basic study of steel-UHPC composite bridge deck is to make full use of UHPC mechanical performance advantage,grasp the fatigue parameters and failure mode of the structure,clarify the fatigue course of the mechanical properties,and explain the changes of the combined effect.The premise of these researches is to understand the tensile working mechanism of UHPC,clarify the strengthening mechanism of steel fiber to its mechanical properties,and accurately judge the change of the working state of UHPC under static and cyclic loads.The UHPC layer fatigue failure mechanism of the steel-UHPC composite deck system is investigated by model tests and theoretical analysis based on the research of UHPC material,composite slab component and composite bridge panel structure.The following works are performed and completed:(1)Strengthening mechanism of steel fiber to UHPC tensile propertiesBased on the existing research results,the microscopic working state of steel fiber was analyzed.The random distribution of steel fiber in cement-based colloid was described.Combined with the cement-based binding working state of steel fiber,the microscopic force model of the interaction between steel fiber and cement base was established.The strengthening mechanism of steel fiber mechanical properties against tensile UHPC was analyzed based on this theoretical model.The model reveals the fiber strengthening mechanism of tensile UHPC at each working stage.Combined with the model test data,a stress-strain hyperbolic model of tensile UHPC was established,and the damage risk of tensile UHPC under cyclic load was analyzed.(2)Static working process of bending steel-UHPC composite slabBased on the tensile UHPC hyperbolic stress-strain relationship,a section strain method was established to reflect the stress distribution of steel-UHPC composite slab.Composite slab test models were designed to verify the correctness of the theoretical analysis method.Combined with the test results and theoretical analysis,the static working process and failure mechanism of steel-UHPC slab were studied.The calculation method of static cracking strength and cracking load was put forward.The results show that reducing the thickness of the protective layer or increasing the reinforcement ratio can effectively improve the cracking load of steel-UHPC composite slab.(3)Flexural deterioration mechanism of steel-UHPC composite slab under cyclic loadingTests were designed to study the flexural deterioration of steel-UHPC composite slab under cyclic load.Based on the theoretical analysis,two types of UHPC fatigue loss processes were studied.The loss of section bending stiffness caused by fatigue loss was calculated quantitatively with neutral axis offset.The analysis shows that the fatigue damage mechanism of UHPC structural layer is related to the upper limit of fatigue load amplitude,and both fatigue damage modes are irreversible.(4)Fatigue deterioration process analysis method of composite bridge deck based on fatigue loss of UHPC layerThe fatigue tests and theoretical analysis of the transverse and longitudinal systems of the orthotropic steel-UHPC composite bridge deck were carried out and the fatigue loss influence of UHPC structural slab was investigated.Combined with the finite element numerical simulation results,the influence of deterioration of steel-UHPC composite effect was calculated.The analysis results show that the conventional test design method for fatigue welding details of steel structures is not suitable for the study of fatigue damage of UHPC layer.