Fatigue Process And Life Research Of Concrete Beam Under Heavy Load

In recent years,the continuous development of traffic and transportation industry and operators' excessive pursuit of interests lead to the proportion of heavy truck load in expressway transportation increasing year by year,and the overloading phenomenon is frequent.Reinforced concrete simply-supported girder bridges take a large part in the highway bridges.Under the long-term fatigue load of heavy trucks,the problems of beam bottom cracking,exposed bar and excessive downward deflection are common in the simply-supported reinforced concrete girder bridges that have served for many years.At present,almost all the basic data of fatigue research on reinforced concrete simply-supported hollow slab beams are derived from the fatigue test of reduced scale beams,while the research based on the fatigue test results of full-scale simply-supported concrete simply-supported hollow slab beams in service is rarely seen.Based on the measured heavy load traffic data of an highway,the fatigue test of the reinforced concrete simply-supported hollow slab beam which has been in service for 23 years was carried out in this paper,and the residual fatigue life and related fatigue problems of the beam were tested and studied theoretically.The main contents are as follows:(1)The types,quantities and total weights of 2188252 heavy vehicles on the highway were obtained by statistical investigation method,and the main data such as axle load and axle base of each typical vehicle were determined.Based on these data,the equivalent fatigue load spectrum of full-scale simply supported concrete hollow slab beams in service is calculated by using the "random load converter" which is developed based on the EM-GMM model,the M-R method principle,the Matlab program and the Visual Basic language.(2)The research group carried out static load and fatigue tests on full-size RC simply supported hollow slab beams in service,obtained the ultimate static load capacity,fatigue strain,deflection and other fatigue related data of the beam,and fitted the fatigue S-N curve of full-size RC test beams in service.In this paper,based on the random fatigue test load spectrum obtained from the measured heavy traffic volume conversion,the deflection and strain data of the test beam under different cycles are analyzed,the equivalent constant amplitude fatigue stress spectrum of the test beam is calculated,and the fatigue life of the test beam under actual vehicle load is predicted according to the fatigue S-N curve.Different from the traditional traffic volume prediction,this paper predicts the long-term traffic volume of the heavy-duty fatigued vehicle on the expressway from the fatigue analysis angle of the reinforced concrete beam,and then calculates the fatigue failure time of the hollow concrete beam in service under the heavy traffic.(3)Based on the synergistic damage theory proposed in this paper,the fatigue constitutive relation of concrete materials is established.Based on Miner linear cumulative damage theory,the fatigue constitutive relation of reinforcement materials is established.Using C# language to write the concrete fatigue constitutive parameter calculation program,through which the concrete constitutive parameters after any number of times fatigue load were calculated.The finite element analysis software ABAQUS was input in the whole process numerical simulation analysis of reinforced concrete slabs with fatigue test results for validation,proved the feasibility of the cooperative damage theory.Based on the synergistic damage theory and failure judgment criterion,the numerical simulation of reinforced concrete hollow slab beams can be carried out,and the fatigue state and fatigue life of the beams can be predicted after any times of fatigue loads.(4)The fatigue stiffness of full-scale reinforced concrete hollow slab beams is studied based on damage evolution model.The damage evolution equation of fatigue plastic flow is derived on the basis of thermodynamics theory,and a two-stage damage evolution model suitable for the development characteristics of reinforced concrete hollow slab beams is derived according to the classical damage evolution equation.Based on the fatigue test results of concrete hollow slab beam,the relationship expression between the stiffness and fatigue times of reinforced concrete hollow slab beam is fitted,and then the fatigue damage degree of reinforced concrete hollow slab beam expressed by stiffness is fitted.The proposed stiffness damage evolution model can be used to infer the current fatigue damage degree and fatigue life of concrete beams from the easily measured concrete beam stiffness in practical engineering.