Analysis Of Distortion Effect In Steel Box Girder And Its Influence Factors

Steel box girder has became more and more popular in bridge construction.Compared with the traditional concrete box girder,the wall of Steel box girder is relatively thiner and the distortion in steel box girder is more significant.The derivation and interpretation of the classical theory of distortion is conducted to figured out the basic concepts.Then,a research on the influencing factors of the distortion effect in steel box girder has been carried in this paper.Finally,the reasonable diaphragm spacing when the distortion effect can be ignored is discussed.Compared the classical theory,the solid element and the shell element of finite element with the measured value of distortion warping normal stress in experiment,it find that the ABAQUS 4-node shell element S4 R controlled by reduced integral and hourglasss is the best method to calculate the distortion effect in box girder,which can help to carry out the further study of distortion effect.Through the orthogonal experiment,the influence of the diaphragm spacing,the diaphragm stiffness,the height width ratio of the section and the thickness of the box wall on the distortion effect is compared for the first time.This study shows that the thickness of beam wall and the number of diaphragms have a more significant effect than the aspect ratio and the rigidity of diaphragms on the distortion effect in box girder.Therefore,this research points out that the most reasonable method to limit the distortion effect of steel box girder is to set several thin diaphragms inside the steel box girder.By setting different number of diaphragms in the box girder with different section height width ratio,this research finds that the distortion effect can be ignored when the ratio of the spacing of diaphragms is less than 1.5 times the maximum size of the section in the steel box girder.By constructing a large number of training samples of steel box girder to train a 4-layer ANN fully,a more accurate calculation formula for reasonable diaphragm spacing of the single box and single chamber steel box girder is obtained.When the diaphragm spacing satisfy the method proposed above,the distortion warping stress can be limited to less than 10% of the bending normal stress,and the effect of distortion can be ignored in steel box girder.