Stress Response And Fatigue Damage Induced By The Buffeting Of The Central Buckle Anchorage Area In A Long-span Suspension Bridge Based On Multi-scale Model Method

The construction of modern suspension bridge is going to be developed towards the direction of super-large span and extreme flexibility,which makes the wind-induced vibrations of long-span suspension bridges more and more prominent.The central buckle can suppress the wind-induced vibration response of long-span suspension bridges to a certain extent and has been widely used.At present,most studies on the central buckle focus on its effects on the natural modal frequency,the wind-resistant and seismic performance of long-span suspension bridges.However,there are few studies on the stress responses and fatigue performance of the long-span suspension bridge under wind-induced vibration.Moreover,the structure and force of the central buckle at the anchorage of cable and main beam are relatively complex,and fatigue failure is easy to occur under long-term wind-induced vibration,which will affect the safe operation of the long-span suspension bridge.Therefore,in this paper,the stress response and fatigue damage of local details in the anchorage area of central buckle under wind-induced buffeting were studied based on the multi-scale model of the long-span suspension bridge established by the parallel uniform multi-scale method.The main work is as follows:(1)Firstly,it briefly introduces the research background and significance of this paper.Then,the status quo is reviewed about the research on the buffeting analysis method of the long-span bridges.The central buckle,multi-scale structure,multi-scale interface coupling method are reviewed,too.Finally,summarize and find the shortcomings of the existing research,and make clear the main content of this study.(2)According to the existing multi-scale modeling methods,a parallel consistent multiscale modeling method was proposed based on the combination of substructure method and multi-scale interface coupling method using the interface virtual work balance principle.The numerical examples of plane beam-plate connection model and 3D beam-shell connection model are developed to verify the advantages of the proposed multi-scale modeling method in terms of decreasing degree of freedom,high computational accuracy and applicability to the analysis of local detail dynamic stress responses of long-span suspension bridges.(3)Taking Aizhai Super Large Bridge as the engineering background,a parallel and consistent multi-scale finite element model of the bridge was established based on the proposed method in this paper,which can consider the local details of the anchorage area of the cable and beam of the central buckle.Then,based on the traditional linear buffeting analysis theory and considering the static wind effect and the aerodynamic force of the main cable,the time-domain analysis of three-dimensional nonlinear buffeting of the bridge is realized through the secondary development using ANSYS APDL language.Finally,the displacement responses of the bridge and the stress response of the local area under the design wind speed are calculated and analyzed,and several key parts in the local area are determined.The stress response time histories of the key position are analyzed.The results show that under the designed wind speed,the anchorage system of the central cable girder located in the downwind side is subjected to complex force and serious tension.The stress amplitude in the anchoring plate(below),the curved cut in the integral joint plate and the web of the vertical belly bar of the main truss are very large,thus,the fatigue failure is easy to occur.(4)Based on the parallel uniform multi-scale finite element model of the long-span suspension bridge,the buffeting analysis in time domain at different wind speeds was carried out.The stress time histories of the key parts under different wind speeds were extracted to evaluate the fatigue life of the structure,and the evolution characteristics of the fatigue performance of the key parts with the wind speed were studied.The results show that:the fatigue life of the key parts decreases rapidly with the increase of wind speed.The detail of the lower anchor plate is more dangerous,and the failure of the central buckle due to fatigue failure is more likely to occur due to the multiple stress cycles under long time wind-induced vibration.Under the wind speed of 44m/s,the details at the arc incision of the vertical web bar of the main truss can only last 0.07 years before fatigue failure.In addition,the maximum stress exceeds the yield strength of the steel.Thus,under high wind speed,strength fracture is very likely to occur in this area before fatigue failure.