Study On Key Technologies For Computer Aided Design Of Box Girder

Prestressed concrete box beam is widely used in the bridge structure now, In structural calculations of complex bridge, use of finite element analysis unit has unique advantages, in the application of the structural finite element analysis, finite element analysis is divided into three steps:pre-processing, calculation and post-processing. Based on past experience, pre-processing is often the longest step. while finite element mesh directly affect the quality and quantity of the calculation precision and speed, so the finite element mesh generation has become a hot research. In the mesh, the more commonly used is the four-node tetrahedron element and eight-node hexahedral element. The former's high degree of automation technology is mature, and it has a wide range of applications, but on the overall performance, especially in terms of accuracy, hexahedral eight-node is more superior. There are many methods about Hexahedral mesh, such as the mapping method, scanning method, grid-based method, the extended AFT method, etc., but the automation and the quality of the hexahedral element can not be taken into account simultaneously, the fundamental reason is that some key issues of hexahedral element is still unresolved. How can it automatically generates high-quality mesh and the grid cell into hexahedral became the bottleneck in the development of finite element calculations.Concrete box beam is now widely used for the box girder bridge structure, about complex bridge structure, there is no highly efficient method of mesh generating. In this paper, on the basis of many years'development CAD software, according to the geometric characteristics of concrete box girder structure, the author proposed a way to automatically complete the concrete box girder with automatic hexahedral mesh subdivision algorithm-the vertical section method.This article uses the python language as a tool, combined with salome computer-aided modeling platform to its own functions and modules to achieve the secondary development of automatic hexahedral mesh subdivision algorithm. The main idea is as follows:1,the preparatory work before the establishment of the geometry model:the geometric model is the completion of follow-up work such as grid based triangulation, in this step we must first establish a reasonable coordinate system. We consider the existence highway horizontal alignment in the circular curve and easement curve, in order to facilitate calculations, in this paper we establish a three-dimensional coordinate system, the L-axis is along the middle line, the S-axis is along the direction of cross-section, and Z-axis is along the vertical axis. The geometry of the concrete box girder is more complex, finite element mesh automatically partition must have a geometric model of the software management capabilities. This article is used Wings edge structure, it is a center to the edge of the data structure of a boundary representation, can well describe the physical point of the relationship between line and plane. In this study, we use Salome CAE software, and the OpenCasCadeis used in geometric modeling module. The OpenCasCade is a geometric model of the open source core of CAE, it can achieve to create basic geometry, Boolean operations, geometry and spatial relationships of the calculation, analysis of geometry and many other functions.2,Construct the salome geometric model. We use the Geometry module to construct the geometric model. Concrete box girder structure in the geometric shape of a polyhedron can be regarded as abandoning the internal section. Based on this idea, first,establish the control section and use pumping concrete box extension of the algorithm to produce the three-dimensional model of external entities, and then use the same method to generate three-dimensional model of internal entities, at last, we obtain the concrete box girder geometry Model by Boolean operations.3,Hexahedral mesh division by the vertical section method:first select the box girder cross section in the reference section for analysis, in which add the node on the selected section. Then based on the reference section, insert nodes to the other sections by mapping method. Finally, connect the eight adjacent nodes to generate hexahedral mesh.While hexahedral mesh established, based on the principle of minimum potential energy, the author raised a calculation of element stiffness matrix considering the influence of reinforced concrete bridge components and the steels. The traditional calculation unit always obtained a smaller result and the improved method changed it. Now we improve the calculation precision, and provide a reliable theoretical basis for the bridge construction projects.