Public Rail Dual-purpose Bridge Boom Fatigue Analysis

Suspenders,which transfer the load from the deck to the arch rib are the key components of arch bridge. It is important to the overall life and safety of bridge whether suspenders can work well or not.With the development of economy,on one hand,more and more bridges have been designed to carry both vehicle and railway traffic; on the other hand,the traffic volume has increased dramatically. With the lighter structure and long span,Bridges may have a greater vibration and stress amplitude of the Suspenders may be large under both moving monorail trains and road vehicles. It is necessary to analyze the fatigue of suspenders.Base on the Caiyuanba bridge,suffered highway traffic and light-rail traffic,the fatigue analysis of suspenders with steel truss beam and tied arch is performed.The major work has been done in this thesis as follows:Firstly, the concept of road spectrum is introduced,and the presently domestic and international research state to fatigue load spectrum is briefly introduced.Secondly, fatigue analysis method of suspenders of arch bridge used for highway traffic and light-railway traffic is presented. The dynamic model of the bridge used for highway traffic and light-railway traffic can be built by FEM method.Fatigue load used for highway traffic and light-railway traffic can be simulated by random traffic flow,which can reflect the parameters of load spectrum. The stress time history of suspenders is obtained under the loads of traffic flow, and then the stress spectrum is computed through the reservoir method. Finally, the equivalent stress amplitude is calculated in accordance with the Palmgren-Miner linear cumulative damage theory, and the assessment of the damage is performed during the design reference period.Thirdly,assocatied programs are developed for fatigue analysis of suspenders using Fortran95.The first program which can produce random traffic flow aotuomatically is developed. The second program which can obtain the the stress time history of suspenders is developed. The third program named the reservoir method used for stress cycle of statistics is developed.Those programs can be used conveniently to perform fatigue analysis of suspenders.Fourthly, The dynamic model of Caiyuanba Bridge is established.Fifthly, Fatigue analysis of suspenders on Caiyuanba bridge is completed.The highways load spectrum and light-rail load spectrum are choosed,then the bi-dimensional multi-line road vehicle traffic flows and light-rail traffic flows are generated based on the method of random traffic flow.After that, fatigue residual life assessment is performed with the Palmgren-Miner linear cumulative damage theory and fatigue S-N curve in different conditions.Results show that suspenders on Caiyuanba bridge would be safe only taking into account both the highways load and light-rail load during the design reference period.