Spatial Finite Analysis Of Urban Intersection

The intersectional part of multi-ramp grade separation bridge has an irregular shape. The stress condition in this part is complicated, which causes the difficulty in the design of this kind of bridge. The conventional finite element method of plane frame can not reach proper result therefore spatial finite element method has to be applied. Taken a real grade separation bridge in Guangzhou, mechanic properties under sorts of is irregular shape beam were analyzed.The finite element model based on grillage and shell-meshed method are both established. The analytical results of stress and deflection from the two methods are closed to each other, which verify the validity of the model of geometry, mathematics and mechanics. Meanwhile it is demonstrated that the grillage method avails in engineering with trusty. It is also concluded in this thesis that the values resulted from the grillage method in the sagging moment region are slightly larger than those from the shell-meshed method. Because of its incapability in taking account of the effect of shear slag and deformity, the grillage method may be only used successfully in the overall structure analysis and should be aided by analytical, shell-meshed or 3-D finite element method for better results thorough comparison. In addition, the imposing of prestressed steel bar in spatial model is a difficulty. But cutting with curved planes model solve the problem in this thesis.The sub-model method is taken used of in the stress analysis in the irregular shape beam. The overall structure with coarse mesh is firstly adopted to calculate the boundary condition of its irregular shape beam that is granted as sub-model, and then the sub-model with the boundary condition is refined in mesh for further calculation so as to carry out an economic computer calculation. The application of the sub-model method makes the detail stress distribution illustrated obviously, which offers effective reference for the reinforcement in the irregular shape beam.The verifying method to get bearing eccentricity of single-point-support curve bridge which is another key factor in the design of overpass is discussed in this paper. By determining the optimization target and setting optimization condition, the optimization method as to bearing eccentricity based on the ANSYS is obtained and some examples is illustrated to certify it.