Study On Static And Dynamic Characteristics Of Concrete-filled Steel Tube Rigid Frame With Arch-steel Box Continuous Beam Bridge

The concrete-filled steel tube rigid frame tied arch bridge has greatly reduced the bearing capacity requirement of foundation because of the tie bar,so it has been developed rapidly and appears more in plain area,urban areas and special geological areas.The concrete-filled steel tube rigid frame tied arch bridge has many statically indeterminate times and the force of the arch bridge is complicated,so it is of great significance to study the influence of basic design parameters on its mechanical behaviors,dynamic characteristics and stability.In this dissertation,based on the an Expressway Bridge,the spatial finite element model is established by using finite element software Midas/civil,and the static characteristics,the dynamic characteristics and stability of the bridge are analyzed.Then by changing the design parameters of the structure,the influence of the design parameters of the concrete-filled steel tube rigid frame tied arch bridge on the structural characteristics is analyzed,the stress distribution of joint of arch and pier is analyzed by finite element software Ansys,and some main conclusions are obtained as follows:(1)According to the static analysis of the bridge,under different load conditions,the concrete in the upper steel tube the abdominal cavity of the arch rib at the joint of the arch and pier have greater tensile stress,which is greater than their tensile strength.The stress of the other parts of the bridge is within the strength range of the material and the stiffness of the bridge meets the requirements.(2)With the decrease of the ratio of rise to span,the axial force of the arch rib increases gradually under the action of dead load and live load,respectively.The mid-span deflection of the main arch rib and the mid-span deflection of the bridge deck system gradually increase with the decrease of the ratio of rise to span,and the increase of the middle span deflection of the main arch rib is much larger than that of the main arch rib.(3)The arch axis coefficient has little effect on the axial force of the arch rib,but has a great influence on the bending moment of the arch rib;the tensile sequence of the tie bar has little effect on the axial force of the arch rib,but has a great influence on the bending moment of the arch rib and the horizontal reaction of the pier bottom.In the course of construction,In the course of construction,it should be avoided to reduce the tension times of tie rod as far as possible.(4)The vibration mode order of concrete-filled steel tube rigid frame tied arch bridge will vary with the rise-span ratio,and the vibration frequencies of various vibration modes will increase with the decrease of the rise-span ratio.(5)The vibration fundamental frequency of the structure is maximum when the "ж" type horizontal brace is adopted.Compared with the "one" type horizontal brace,the transverse bending fundamental frequency of arch rib increases by 163.97% when the "meter" type transverse brace is adopted.The vibration fundamental frequency of concrete-filled steel tube rigid frame tied arch bridge increases with the increase of the number of transverse braces.(6)With the decrease of the rise-span ratio,the load safety factors of the buckling modes of the bridge structure decrease continuously.The load safety factor of the first-order buckling mode is reduced by 26.68% when the ratio of rise-to-rise to span decreases from 1/3.5 to 1/5.5;(7)The load safety factor of concrete-filled steel tube rigid frame tied arch bridge with "米" type transverse brace is the largest.The buckling instability fundamental frequency of concrete-filled steel tube rigid-frame tied arch bridge increases with the increase of the number of transverse braces.The overall stability of arch bridge can be improved by raising the grade of concrete in arch ribbed steel tube or increasing the thickness of arch rib steel tube.(8)Most of the piers are in the state of compression.The tensile stress at the bottom of the pier is concentrated on the outside and the maximum tensile stress reaches 13.86 MPa,so in the design process,relevant measures should be taken to reduce the tensile stress here.At the joint of arch and pier,the concrete in the upper steel tube is under tension and the tensile stress is large,the concrete in the lower steel tube is compressed and the compressive stress is small,and the upper and lower steel tubes are in the tensile state,and the tensile stress meets the strength requirement.