Study On The Detail Structure And Mechanical Properties Of External Steel Anchor Pipe Anchoring Structure For Stay Cable

The external anchorage structure of cable-stayed bridge has the advantages of being convenient for cable system inspection,maintenance and replacement construction,but the detail structure of the anchorage structure is complex and the structural stress is concentrated,so it is necessary to pay more attention to its mechanical properties in the bridge design.This paper relies on the "Science and technology demonstration project for safe and intelligent construction of Feng jian Expressway in the Three Gorges Reservoir area" project of Ministry of Transportation.Based on the design principle of anchorage structure of cable-stayed bridge,the influence of detail structure of anchorage structure with external steel anchor pipe on the force and deformation of the structure is studied.The sensitivity analysis of structural parameters is carried out by ANSYS fine finite element model,and the optimization design of the external steel anchor pipe anchoring structure is carried out,and the static and fatigue performance of the structure is further studied,which provides technical support for the promotion and application of entity engineering.The main work and conclusions of this paper are as follows.Firstly,based on the design principle of cable-stayed bridge anchor structure and the structural characteristics of built-in anchor pipe,the preliminary design structure of external steel anchor pipe anchor structure is proposed.The sensitivity analysis of design parameters of the anchorage structure was carried out.The internal relationships between structural dip angle,thickness and chamfering radius of anchoring webs,thickness and number of stiffeners,thickness of anchor pipes and structural performance were explored.The key design parameters of dominant structural performance were determined as thickness of anchoring webs,chamfering radius and thickness of anchor pipes.In view of how to further improve the bearing capacity of the structure,five structural measures are proposed for reference.Secondly,through the sensitivity analysis of the anchorage structure of key design parameters,the mathematical model is designed on the further basis of structure optimization.Taking the anchoring web chamfering radius and anchor pipe diameter as an input parameter,and structure of the maximum equivalent stress as an output parameter,the optimize design is carried out by using of screening optimization method.The relationship of the fitting formula and the response between input parameters and output parameters is established.On the basis of that,the external type anchorage structure optimization design scheme is put forward.Thirdly,relying on science and technology demonstration project,comparative study on static performance of external anchorage structure is carried out.The MIDAS integral finite element model of the bridge,the ANSYS fine finite element model of the initial design and optimized design of the anchorage structure section beam body are established,and the stress and deformation rules of the anchorage structure are compared and analyzed.The stress concentration of anchoring structure is found in the center of arc of anchoring web.The Mises stress at the stress concentration of the anchorage structure was decreased by 12.67% with the increase of the web chambered radius by 1.5%.The stress distribution at the lower end of the anchoring webs welded with the main girder webs and steel anchor pipes is larger,and the ultimate bearing capacity of the optimized structure is increased by 3.0%.Fourthly,relying on the science and technology demonstration project,a comparative study on the fatigue performance of external anchorage structure is carried out.The ANSYS fine finite element model of the anchoring structure section beam body was established.The high cycle Fatigue analysis of the structure was carried out by Workbench Fatigue Tool.The S-N curve was carried out by the JTG D64-2015 code of China and the BS5400 code of Britain.Structural fatigue life analysis is carried out by Paris formula in fracture mechanics theory.The results show that the fatigue normal stress and the fatigue shear stress at the center of the circular arc of the anchorage web of the optimized structure are reduced by 22% and 19%.The fatigue life of the welded site between the steel anchor pipe and the anchor web is 214 years when the initial crack depth is 0.5mm,and the stress intensity factor threshold value is 40 mm.When the width of the initial crack is greater than 0.15 mm,the fatigue life of the structure is greatly affected.The research results are instructive for machining and welding of external anchoring structure.