| In the steel-concrete composite deck structure,bolt is an important force transmission component,which is the key to ensure the coordinated force between steel beam and concrete,and its function is to transfer the inter layer shear force and prevent the rise of concrete slab.In recent years,UHPC has been widely used in steel-concrete structure because of its advantages,and it forms a new type of cross-section(steel UHPC composite deck structure).The change of structure form will lead to stress redistribution of composite deck.Therefore,it is of practical significance to study the mechanical characteristics of bolt and steel deck under UHPC pavement.Through the shear nail push out test and a practical bridge case of a steel UHPC composite structure,the main research contents include:(1)The influence of different concrete materials,bolt diameter and bolt length on shear capacity and load slip curve of bolt in steel UHPC composite structure is studied by launching test.(2)Based on the test,ANSYS model is established to analyze the shear performance of the bolt.The influence of four factors(concrete compressive strength,bolt diameter,ultimate tensile strength of stud and ratio of length to diameter of bolt)on the shear bearing capacity and load slip curve of the bolt is studied;the stress distribution law and difference of long and short studs are studied;the formula and load-bearing capacity calculation formula and load of shear nail are deduced The slip curve equation.(3)Through a real bridge case(orthotropic steel UHPC composite bridge deck structure),the influence of bolt spacing and diameter,concrete pavement material and thickness of UHPC pavement on the static and fatigue energy of four parts of bridge deck structure(concrete layer,steel bridge deck,steel bridge deck,steel bridge deck plate,steel bridge deck plate and bolt bolt weld joint)is studied.The main research results and conclusions are as follows:(1)The results show that,on the basis of the determination of bolt and I-steel material,the diameter of the bolt is the main factor affecting its shear capacity,the second is the concrete strength,and the length of the bolt is less affected.The calculation of the bearing capacity of the bolt in UHPC is conservative by the existing codes.The slip curve of bolt load shows that increasing the diameter of bolt can improve the bearing capacity and ductility,and the strength of concrete can improve the bearing capacity,but the ductility of the specimen decreases.(2)The results show that the concrete strength,the diameter of the bolt and the ultimate strength of the material have a great influence on the shear capacity,while the ratio of the length to diameter of the bolt has little influence.The distribution of shear stress is as follows:the stress at the root of the bolt is the largest,and it decreases rapidly in the direction of the nail cap;the diameter of the bolt increases,the slenderness ratio decreases,and the effective length of the stress distribution along the bolt increases.Based on a large number of measured data,the calculation formula and load displacement curve equation of ultimate bearing capacity of bolt are derived,which are suitable for the situations of concrete strength greater than 35 MPa,ratio of bolt length to diameter l/d>2 and shear failure of bolt.(3)A method of calculating shear force of bolt by relative displacement between layers is proposed in the segment model of steel-concrete composite beam,which is suitable for simulating bolt with spring element.The distance and diameter of the bolts have a great influence on the composite deck structure.UHPC layer has a great improvement on the local and overall stiffness of the deck,and the effect of improving the stress distribution of steel deck is better than C50.The increase of UHPC thickness is more favorable for the composite deck. |
