Analysis Of Shear Lag Displacement Function With Generation Algorithm And Neural Networks

With the development of material science and transportation, thin-wall box girder (including steel girder and prestressed concrete girder) is used wildly in modern engineering of bridge, but shear-lag problem is arising accordingly, the result it takes can not be ignored, especially broad and low box girder. The consequence is, when the majority of structure doesn't enter yield habitus, but the position of belly-board has been reached the ultimate habitus, it lead to material waste of the other positions, we should pay attention to the disastrous result it will bright to us. The analysis of shear lag has an important significance on safety and economy to the design of modern bridges. But there is divergence on the selection of displacement function. So what is the form of displacement function be like has been an important subject.Recent years, GA (generation algorithm) as a hot subject is wildly used all over the world. It is a very effective method of curve fitting. In this paper, the author chooses many box girder modules with different dimension justified and analysis the modules with FEM (finite element method). The result of FEM is fitted with GA, coefficient of fitted functions can be got.NN (neural networks) is a powerful tool in analysis of non-linear problems, it used in prediction, classification, pattern identity, procedure control and so on. In the paper, a BP networks is founded to show the relationship of the box girder dimensions and load's peculiarity with the parameters of fitting. So we can use the networks to identify the function parameters when a box girder module is defined. The outputs of the networks are the coefficients of the bias function to displacement function, the bias function is used to adjust displacement function. The method avoids deflection of the other displacement function aroused.In the end of the paper, two examples are analysised, the samples tell us the displacement function with adjust coefficient has advantages of high accuracy and simple. It is a new method to find the displacement function form in analysis of shear lag effect on thin-walled box girder.