Assessment On The Fatigue Life Of Steel Bridge By Grey Theory

With economic development, China built a large number of bridges. As one of the important factors in controlling the life of the bridge, fatigue issues is now increasingly being concerned by people. Research on the fatigue life of the bridge will not only help to extend the useful life of bridges, but also provide theoretical support for the regular maintenance.When using traditional methods to study the fatigue of bridge components, collecting a lot of stress history data is needed, which makes the low efficiency of research work.And inadequate spectral data would cause that evaluation results appear agreat deviation. At the same time, the effectiveness of the gray theory in forecasting becomes increasingly significant, it goes on little data and poor sample of the fatigue life of mechanical structures and components for effective forecasting. From this perspective, the gray theory is introduced to study the fatigue life of the steel bridge on the different components.With the help of the Midas Civil and Matlab software and building on the existing steel bridge fatigue analysis and forecasting methods, we could take a series of estimates on fatigue damage and remaining fatigue life of the new CaiShi bridge.The gray theory is introduced to establish the gray prediction model on the base of damage degree and then forecast with four different methods, the main contents are as follows:(1) A brief description of the specific steps of the remaining fatigue life assessment of steel bridges based on the linear cumulative damage theory, and so is determined the basic idea of the new CaiShi bridge fatigue damage analysis.(2) With the help of Midas software, analysis model of the bridge is established.and then affacting lines of different bars are solved; Loading the virtual vehicle load and simulating the stress processes of four kinds of rods at different times. Compiling spectrum and calculating the fatigue damage degree and the remaining life of different rods. The results show that, under the same load time,four degrees of the fatigue damage of the rods are basicly in the same level, but the4th rod is greater, and thus has a shorter fatigue life.(3) Establish the standard GM (1,1) model based on the traditional degree of the fatigue damage and then carry out assessing the degree of damage. The results show that the fitting accuracy is over90%, but the prediction error is much larger.Improving model to try to reduce the error value.the calculation and analysis shows that the GM (1.1) model based on the arccot transform, not only improves the fitting accuracy but also makes the deviation of the predicting value smaller, so the model is more effective,while the other two models cannot make the fitting accuracy and the deviation of the predicting value significantly improved. In summary, in the assessment on the degree of the fatigue damage and the remaining life of the steel bridge, the application of the gray theory can achieve better results,but improving the model helps to increase the accuracy of the prediction.