Global Stability Analysis Of Single Tower Cable-stayed Inverted Siphon

Based on the design ideas and experience of Long-span Cable-stayed Pipeline bridges,this paper uses the overall stability theory of cable-stayed bridges to rationally optimize the structure.The dynamic analysis of the structure is carried out by using the seismic theory.The seismic characteristics of single tower cable-stayed inverted siphon under earthquake are studied.The main research contents are as follows:(1)By reading a large number of documents on cable-stayed pipe bridges,we can understand the design characteristics of cable-stayed pipe bridges,and use Midas Civil software to establish a three-dimensional finite element model of single tower cable-stayed inverted siphon.According to the actual situation,boundary conditions and loads are applied to determine the reasonable state of completion of the bridge;(2)Three structural systems have been established.By studying the displacement of inverted siphon beam and main tower under the condition of reasonable bridge completion,it can be concluded that the deformation of inverted siphon beam will greatly affect the stability of the structure.Through linear analysis,the first five orders of modes show that the main tower participates in the deformation.Finally,the structural system I is determined to be the most reasonable;(3)Based on the design of cables,changing the area of cables,focusing on the cable forces and stresses under the condition of bridge completion,the law of increasing the stress and force of cables with the increase of area is obtained,and the reasonable interval of optimizing the area of cables is found out,and the rationality of redesigned area is proved by linear stability analysis;(4)Because the linear expansion coefficient of most materials of the structure is large and the sensitivity to temperature is great,different heating and co oling conditions are established according to local actual conditions.It is analyzed that the change of structure temperature has little effect on the cables,but it has obvious effect on the axial stress of the main girder and tower of the structure.When the structure is cooled down,the main beam is tensioned axially and the main tower is compressed vertically,so the safety and stability coefficient is large.When the structure is heated,the main beam is subjected to axial compression,the main tower is subjected to vertical tension,and the safety and stability factor is small;(5)By establishing expansion joints to reduce the influence of temperature on the structure,four boundary conditions are set up to discuss how to place expansion joints to minimize the structural stability caused by temperature reduction.It is determined that expansion joints should be set at the joints of inverted siphon beam with left and right piers and main towers;(6)The response spectrum analysis method is mainly used in the seismic analysis of structures.The eigenvalue analysis makes the dynamic response of structures meet the requirements of the code,and analyses the influence of earthquake on the displacement,internal force and stress of structures,and obtains the influence of earthquake on the seismic performance of structures.