Experimental Study On Fatigue Behavior Of UHPC Layer Of UHPC-Steel Orthotropic Bridge Deck

In order to solve the problems of damage and fatigue cracking of orthotropic steel deck pavement(OSD)based on the requirements of the development of composite bridge structure,scholars at home and abroad proposed to use UHPC instead of NC and steel deck to form a new type of concrete-steel composite structure,namely UHPC-steel orthotropic bridge deck structure.Taking FA auxiliary road of Foping Road overpass as engineering background,in order to explore the flexural-tensile fatigue performance of UHPC layer of UHPC-steel orthotropic deck structure under different reinforcement ratios and the experimental phenomena of orthotropic steel deck under fatigue load,the fatigue test of UHPC-steel composite deck was made.In the second chapter,the material properties and mechanical properties of UHPC layer,orthotropic steel deck and reinforcing bar in UHPC-steel orthotropic deck are introduced respectively.UHPC-steel orthotropic bridge deck fatigue test adopts UHPC formulation developed by our team,in which steel fiber type is 16mm end hook type and volume content is 3.5%.The raw materials,preparation process,maintenance process and material properties of UHPC mixture developed by our team are introduced emphatically.In this paper,the expansion,compression and four-point bending tests are used to obtain the configuration in fatigue test.The flexural toughness index and energy absorption value of UHPC specimens are calculated by using the expansion,compressive strength,flexural strength and bending stress-deflection curves of UHPC mix ratio,and combining with the stress-deflection curves and relevant codes.The above material performance index is excellent,which is far beyond the design and construction requirements of Foping Road overpass.The cracking area of UHPC layer was identified by finite element model simulation.All the preparations before fatigue test are briefly described,including the specific size of components,the pouring scheme of UHPC layer,the layout of measuring points,the formulation and loading scheme of fatigue load,the fatigue loading process,etc.It lays a foundation for the analysis of fatigue test results of UHPC-steel composite bridge deck in Chapter 4.Through the fatigue test of UHPC-steel orthotropic bridge deck structure,it is concluded that compared with the lower reinforcement,the average strain of high reinforcement is smaller after each cycle.With the increase of cycle number,the loss of stiffness is smaller and the related fatigue performance index is better.The surface fatigue crack of UHPC begins at the pure bend section of UHPC layer with low reinforcement ratio near the root of cantilever end.With the increase of fatigue cycle number,other parts of the pure bend section begin to produce.The transverse penetrating cracks eventually appear near the center of the crack.The depth of the crack is 20.33 mm and the width of the crack is 0.08 mm.Using S-N curve calculation,it is concluded that UHPC-steel orthotropic bridge deck in Foping Road overpass can also meet the engineering requirements by using UHPC layer with low reinforcement(steel bar spacing is 80mm)in combination with the material prepared by our team.