Finite Element Analysis Of Prestressed Concrete Continuous Girder Bridge’s Fatigue Strength

Due to the rapid expansion of traffic volume and severe overloading,most of the pre-stressed concrete bridges with a long service life bear the loads that exceed their design expectations,and there are serious problems such as pre-stress loss.At present,the fatigue problem of prestressed concrete bridges with a long operating life in our country has been very prominent.The fatigue calculation method based on infinite life design in the existing codes has gradually been unable to meet the needs of the society.On the other hand,with the increasing demands of environmental protection,energy saving and safety,the quantitative design of bridge fatigue life will also become an inevitable trend.Therefore,this paper applies the finite element analysis method combined with the metal fatigue theory to evaluate the fatigue life of the prestressed concrete bridge,and explores the method of quantitative analysis of the fatigue life of the bridge.The main research contents and results are as follows:(1)Comparing the advantages and disadvantages of different modeling methods and combining the characteristics of the research objects in this paper,the combination method and the solid reinforcement method are analyzed and confirmed to model the prestressed concrete bridge.Based on the results of a prestressed concrete fatigue test beam a finite element model was established.The joint displacements of concrete and steel bars were coupled through constraint equations,and the reasonable element side length of the model was determined on the basis of comparison and analysis with the experimental results.It is most reasonable when it is 2cm.(2)The finite element model was established with the certain prestressed concrete continuous beam bridge as the object,and the structural strength analysis was carried out under the three working conditions of self-weight,self-weight+lane load and self-weight+overloaded vehicle load;due to the fatigue load and other factors the actual situation that the effective prestress value of the lower prestressed steel bar will be significantly reduced,the bridge prestress loss rate is further set to 20%,40%,60%,and 80%in four typical cases,and the structural strength is analyzed.The results show that the tensile stress of the main force ordinary steel bar will become a possible dangerous part of fatigue damage as the prestress loss increases sharply,so fatigue life evaluation is required.(3)The finite element model for fatigue life evaluation is established with the main stressed ordinary steel bar as the object,and the fatigue life evaluation of the bridge is carried out by using the metal fatigue theory and method.The results show that fatigue failure will not occur when the prestress loss rate is less than 60%;when the prestress loss rate reaches80%,the fatigue life is 1.432 million times under the lane load condition,and the fatigue life is 0.754 million times under the overloaded vehicle load condition.(4)The method in the code is used to evaluate the fatigue of the main stressed ordinary steel bars,and compare the methods in the code with the fatigue evaluation results,and it can be found that the fatigue limitΔf_y~f of steel bars given by the code is more reasonable when the stress ratio is close to 0,but lacks rationality when the stress is relatively large.The theory and method of metal fatigue are suitable for the quantitative analysis of bridge fatigue life,but our country currently lacks the relevant parameters of the bridge fatigue strength design,which need to be accumulated and improved as soon as possible in the future.