Study On Nonlinear Stability Of Long-span Continuous Rigid Frame Bridge With High Piers In Mountainous Areas During Construction

In recent years,the development of bridge industry in China has achieved a qualitative leap.Most of the world's famous bridges are designed and constructed by our country.However,with the development of construction technology,the bridge gradually presents the situation that the larger the span,the higher the pier height,and the worse the construction environment.High pier and long span continuous rigid frame bridges are often used in mountainous areas and gorges because of their strong spanning capacity and high pier height,and the structural form is becoming lighter and thinner,which also leads to the stability problem of this type of bridges more prominent.In this paper,the main span of Lingxianhe Bridge(85+160+85)m is selected as the research object,and the stability of Long-span Continuous Rigid Frame Bridge in mountainous area is studied.Based on the first kind of stability theory,the bare pier,cantilever construction,maximum cantilever stage and the stability of the whole bridge are analyzed and studied by using the finite element software MIDAS.At the same time,the factors affecting the stability of pier structure,such as tied beams,pier thickness,spacing between limbs and piers of different structural forms,are analyzed and studied,and the minimum limit of single factor satisfying the stability factor requirements is obtained.The dynamic analysis of the maximum cantilever stage is carried out,and the expressions of different order vibration modes and their natural frequencies are obtained.When using ANSYS simulation software to study the non-linear stability of Lingxianhe Bridge,the selection of element,constitutive relation(constitutive relation,ultimate compressive strain)and load combination is analyzed and studied.The initial geometric defects in different directions under the highest bare pier state are analyzed and studied.It is found that the deformation state of the structure is not consistent with the initial geometric defects of each pier in different directions.Compatible with mechanical properties.The research results of initial geometry and initial material defects in the maximum cantilever stage show that the ultimate bearing capacity of the structure is the worst when the initial material defects appear in the middle and lower stages,and the larger the initial geometric defects,the worse the stability performance of the structure.The influence of transverse wind load on structural stability(ultimate bearing capacity)is greater than that in other directions.The ultimate bearing capacity of concrete increases by 33.3% for every strength grade.Increasing the number of transverse beams has little effect on increasing the ultimate load.The ultimate load of Lingxianhe Bridge increases by only about 1% for every additional transverse beam.When the tie beam reaches three,the ultimate load of Lingxianhe Bridge increases at the maximum cantilever stage.The change of load coefficient is not obvious.How to select the ultimate compressive stress in the constitutive relationship of concrete has a great influence on the ultimate bearing capacity of the structure.