Fatigue Study Of Long Span Steel Truss Suspension Bridge Members Under Unsteady Pulsating Wind

Suspension bridge has simple structure and clear force,which is suitable for building in areas with large span requirements.However,the wind environment in mountainous areas is relatively complex,and the span and stiffness of bridge structures are relatively large,making their response to wind loads more sensitive.This makes wind resistance design an indispensable part of bridge design.The wind load acting on suspension bridge is mainly divided into static load and dynamic load.The dynamic load mainly refers to the buffeting force generated by fluctuating wind on the bridge structure.Under the influence of buffeting force caused by pulsating wind,the suspension bridge structure will produce alternating stress,which will reduce the life of its components,and then affect the normal use of the structure.In recent years,data on measured wind speeds have shown that fluctuating winds in mountainous areas have strong non-stationary characteristics,In previous studies,they were all simulated as stationary stochastic process,but this simulation was not suitable for mountain environment;Because of the non-stationary characteristics of fluctuating wind,the traditional stable buffeting analysis method is also not suitable for the wind vibration response analysis of suspension bridge in mountainous areas.This thesis investigates the buffeting fatigue of the main components of a long-span steel truss suspension bridge in a mountain region,as it is impacted by non-stationary wind speed.The research is based on the time domain analysis of the non-stationary buffeting response and fatigue damage theory of the bridge.The following are the primary research findings and conclusions:(1)The harmonic synthesis method simulates the stationary stochastic process,which is then modulated by evolutionary spectrum theory to acquire non-stationary wind speed samples.Subsequently,its self spectrum is compared to the corresponding specification spectrum to evaluate its rationality.Subsequently,the non-stationary nature of the data was detected through chi square testing.(2)Establishing a finite element model of a long-span steel truss suspension bridge,compiling an unsteady buffeting response analysis program,and converting the previously simulated non-stationary wind speed time history into a time-varying static wind load and non-stationary one-this is the project’s basis.Shaking force acting on the bridge,and then solve the non-stationary shaking response time history of the bridge through finite element software,laying the foundation for subsequent fatigue damage analysis.Finally,analyze the parameters of the modulation function and study the impact of changes in parameter values on non-stationary buffeting fatigue.(3)By analyzing the non-stationary buffeting response of the bridge,the results indicate that the stiffening beam is the weak point of wind induced fatigue damage,and that the stiffening beam is the most unfavorable component for wind resistance of the bridge.Combined with the rain flow counting method,by comparing the buffeting stress response time history of key nodes of suspension bridge under the influence of steady and non-stationary fluctuating wind,it is found that under the influence of time-varying average wind speed and modulation function,the number of stress cycles of the bridge in the section with relatively large stress amplitude under the action of non-stationary fluctuating wind is more,indicating that the fatigue life of the bridge under non-stationary buffeting is less than that under the steady state.Regardless of whether it is a non-stationary wind field or a stationary wind field,the fatigue life of components on bridges will show a decreasing trend with the increase of the time-varying average wind speed or average wind speed value.By changing the modulation function coefficients and only changing the parameters",it was found that when α=300,it is the most unfavorable modulation function model;As the βvalue increases,the fatigue damage value of bridge components will correspondingly increase,and as the β value decreases,the fatigue damage value of bridge components will correspondingly decrease.