Parameter Study On Fatigue Performance Of Prestressed Reinforced Concrete Beams

Prestressed concrete structure is widely used in modern engineering structure because of its lighter self-weight and good crack resistance.Many reinforced concrete engineering structures,such as crane beams,road bridges and large marine protection projects,will be subject to long-term repeated load effect.Under the effect of long-term repeated loads,the damage of the internal materials of the structure is constantly accumulating,and the fatigue resistance of the components gradually declines,even leading to the fatigue failure of the entire structure.Therefore,the fatigue performance analysis of reinforced concrete structure has become an important research direction in structural engineering.In this paper,the fatigue failure mechanism of concrete beam structure is studied,a new fatigue evolution equation based on residual strain of concrete is derived,a new fatigue life forecast method of prestressed concrete beam is established,and the influence of different parameters on fatigue performance of members is analyzed.The proposed new model and method have certain reference value for the fatigue state evaluation of prestressed concrete beam structure.The main research contents of this paper are:(1)The fatigue performance of reinforced concrete flexural members is summarized,and the fatigue performance of concrete,steel bar and prestressed steel strand is discussed.On this basis,the appropriate damage model and fatigue criterion are selected to analyze the fatigue of the material and determine its fatigue strength.(2)Considering the damage mechanism and evolution process of the material,an improved fatigue evolution equation with residual strain of concrete as the damage amount is proposed.Based on the development law of fatigue failure of concrete materials and the explicit expression of the influence of classical fatigue load stress ratio and stress amplitude on fatigue,the material coefficient in the fatigue damage evolution equation is redefined.The validity of the fatigue damage model is verified.(3)A new method to determine the initial residual strain is proposed,and a new method to forecast the fatigue life of members is proposed by analyzing the normal section stress of prestressed concrete beams and combining the fatigue failure criteria of materials.Based on the principle of "consistency" of cyclic load loading and unloading in Mander model,the initial residual strain value of concrete is obtained,and the fatigue damage model represented by initial residual strain of concrete is obtained.The initial residual strain obtained by this method has high accuracy and can greatly save the loading time of fatigue test and avoid the large errors caused by excessive termination and restart loading in the test process.The fatigue life forecasting method proposed in this paper is used to carry out a batch of prestressed concrete beam fatigue life forecasting.The simulation results are compared with the existing test results.It is found that the fatigue life forecasting is in good agreement with the existing test results.It shows that the proposed method is feasible.(4)According to the pre-stressed concrete beam fatigue life forecast method proposed in this paper,many uncertainty parameters in structural resistance analysis were selected,and the effect of different parameters on component fatigue performance was studied.Among them,it mainly includes material performance parameters(such as concrete elastic modulus,reinforced yield strength)and geometric parameters(such as the thickness of concrete protective layer,the position of prestressed ribs).Changes in these parameters can affect the fatigue performance of prestressed concrete beam structures.The effect on fatigue life was most obvious with concrete elastic modulus and the height of prestressed ribs from the bottom of the beam.For prestressed concrete beams designed according to the specification,with other parameters remaining unchanged,only when the initial elastic modulus of concrete increases by 10%,the fatigue life forecasting decreases by about 4.2%,and when the initial elastic modulus of concrete decreases by 10%,the fatigue life forecasting increases by about 8.3%.