The Critical Distance Method For Fatigue Life Prediction Of Welded Structures Of Bridge Under Random Loading

With the in-depth study of bridge engineering,it is found that most bridge accidents are related to fatigue failure of welded steel structures.In practical engineering,the fatigue caused by vehicle loads on bridges is usually random fatigue.Because the fatigue failure mechanism of welded steel structures under random loads is extremely complex,it is of great theoretical significance to study the fatigue strength and predict the fatigue life of welded steel structures under random loads.And engineering application value.In this paper,the fatigue life prediction of welded steel bridge structures under random loads is discussed.In this paper,the vehicle load model in European Highway and Bridge Fatigue Code is used to simulate the diversity of vehicle data.The Monte Carlo stochastic theory is used to analyze the vehicle random load,and the practical stochastic load spectrum is obtained.The amplitude and frequency of the random load spectrum were counted by rain-flow counting method,and the fatigue damage caused by each amplitude was accumulated by Miner damage accumulation theory.Combined with S-N curve of welded steel structure,the fatigue life prediction method of welded steel structure under random load is established.In this paper,the three-dimensional finite element theory is used to study the numerical simulation of the temperature field of welded steel structures.The,life-and-death element technology,is used to simulate the filling and solidification of solder in the actual welding process,and the internal heat rate model is used to simulate the welding heat source movement.The temperature distribution law of the whole welding process is obtained through calculation and analysis.On this basis,the welding residual stress field caused by welding process is studied.Through the three-dimensional thermo-mechanical coupling finite element analysis,the three-dimensional welding temperature field was transformed into the welding residual stress field,and the stress-strain field nephogram was obtained at all times during the welding process.In this paper,the critical distance theory is used to determine the average stress in the semi-cylindrical region near the weld as the fatigue failure control parameter,and the critical distance R in the critical distance volume method is determined.Considering the influence of welding residual stress on fatigue strength,the prediction formula of S-N curve equation of welded steel structure is given by introducing it into the prediction model of effective force concentration coefficient,and the prediction method of S-N curve based on critical distance theory is established.The fatigue life prediction of plate welded steel structures under random loads is studied by using the fatigue life prediction method established in this paper.White noise is selected as random load spectrum to simulate the residual stress field of plate butt welding steel structure.The fatigue life prediction results are obtained by critical distance theory and S-N curve of plate butt welding,combined with rain flow counting method and Miner cumulative damage theory.The results are compared with those calculated by nominal stress method and Hot-spot stress method.Taking Guiiua Bridge(Suspension Bridge)as the engineering background,this paper analyzes the traffic load near the suspension bridge and obtains the corresponding load spectrum.On this basis,the numerical simulation analysis of the local welded steel structure of the suspension bridge is carried out,and the fatigue life of the welded steel structure of the bridge is predicted by this method.