| At present, Chinese bridge CAD technology is going ahead all over the world because of strong technology research organized by the department of transportation in a great way during the seventh-five planning and the ninth-five planning. But now as far as bridge CAD technology is concerned, in the course of structure analysis, beam element is mainly used,though three-dimension shell element and solid element are partly used, which is immature. It directly produces two-dimension plane working drawing at the aspect of drawing. Analysis program and drawing program is independent basically, which can take on main part design work, but it is necessary to finish some work through manual calculation and manual drawing as auxiliary way. In the course of project design, aiming at important project, it often need use some three-dimension software such as 3DMAX to draw romance picture in order to watch whole effective map. In the course of structure analysis, bridge's superstructure and substructure often need not only use different program but also prepare different data, and it is difficulty in analyzing relatively. And in the course of drawing, it also uses different program to analyze bridge's superstructure and substructure. And it often need prepare a suit of data for drawing of some components such as walkway. So taking a project of bridge design must prepare many repetitious data, which brings large data redundancy and results in possibility of error and wastes much working time. And design process is the continually optimized process, which need modify parameter such as component's size and material's property many times. So every modification will lead to modify large amount of data file, which badly influences the improvement of design efficiency and design quality. Based on the deficiencies mentioned above in bridge CAD system, at present, people doesn't satisfied with the CAD system whose object is only as drawing or analyzing, and expects new CAD system that can assist the whole bridge design process. On the basis of analyzing the question about properties and methods of bridge engineering design, this paper makes approach about integration CAD technology to bridge design. Aiming at the question mention above, we conclude that bridge design is run around a concept model in the brain of bridge engineer. In design process, it continually perfects this concept model through structure analysis, finally choose an optimal project under many constrained conditions such as usage function and criterion and norm and natural condition and project investment. In order to actualize thinking mentioned above, it must solve: ①concept model's express in computer and the method of building model; ②conversion method from concept model to analysis model; ③computational method about analysis model; ④modification method about concept model; ⑤automatic conversion method from concept model to construction drawing. Bridge structure's whole concept model should consist of geometric model data and material model data and constructional method data, in which geometric model data is the most difficult to be managed and expressed. In this paper, it takes solid model technology to manage bridge's geometric model data. Up to now, the research domain of using solid model technology to express accurate and integrated civil engineering data is blank. Obvious character of geometric model of civil engineering structure in its topological model is that construction boundary surface and material boundary surface exist in structure interior. After possessing construction boundary surface and material boundary surface, topological model of bridge structure becomes unpopular structure's radial-edge model, which can prescribe unpopular structure. But radial-edge structure lacks a layer structure of expressing construction paragraph, when structure constructs along different paragraphs, building model will encounter difficulty. So we makes modification to radial-edge structure in research, which is adding a layer Paragraph information on its shell structure and solid structure. But the relationship between Paragraph and Shell isn't inclusive completely. A box beam possesses possibly one internal Shell and one external Shell, when it is divided into many construction paragraphs, if relationship between Paragraph and Shell is defined as up layer and down layer, a box beam's internal shell and external shell will be divided into many other type's shell because of Paragraph, which will result in the loss of structure's original geometric meaning and add working time to structure modification. Based on above thinking, this paper makes modification to topological model of structure, which is setting up parallel relation between Paragraph and Shell. The solid model for bridge involves many curves and surfaces. When bridge includes transition curves, the curves must involve transition curves and the parallel curves of transition curves. The surfaces that are made up of these curves are very complicated. We deduce the equations of the transition curves'parallelcurves and describe the surface with limited plate one linear surface in the system of solid model for bridge. It is important for solid model to modeling, and editing and inputting whose work decides whether the technique of solid model is worth to designing work. Previous methods of modeling, editing and inputting for solid model are the generation of basic body elements and scanning, the set operations and the surface sculpturing etc, which are convenient to the numerous modifications of model. It provides an operator for adding nodal lines, which can modify the topological data inside the solid modeling system directly without any sophisticate set operation. In addition, it provides an algorithm for scanning curved bridges with variable width, which can produce topological and geometrical data directly from bridge transects and road center line data. The new algorithm is suggested in engineering practice, whose practicability is strong. Structure analysis is important in bridge design, at present, all complicated bridges'structure analysis depends on the FE software. Solid model data can completely express data suck as bridge's geometric information and construction information, if it could directly produce FE meshes from solid model data, working efficiency would be improved. In bridge engineering, concrete component is of a certain degree thickness, so it is suitable to analyze with body element, whose element mesh can meet complex geometric shape and has higher precision. Hexahedron element is superior to tetrahedron element in lots of aspects and computational precision. But the preparation for the mesh data of body element will spend much time. Though many research working, the problem of the completely automatic hexahedron mesh generation for complex three-dimension entity could not get the solution on genuine meaning all along. In the research, we try two methods to generate hexahedron in bridge structure. Those two methods bases on the same concepts: ①Concrete bridge's superstructure is composed of thin wainscot components, nodes except some special nodes would be allot on component's surface. ②In bridge design, the phenomenon of stress concentration is avoid appearing, high stress gradient region is little, so it uses comparatively homogeneous meshes according to geometric shape in computation. Aiming at those two characters, we suggest the first algorithm: ①Dispose nodes in every shell surface with same size and establish connective pointer between nodes. ②Two parallel surfaces in thin wainscot components are named as correspondingsurfaces. We suggest five kinds of topological and analytic conditions to establish connective pointers between nodes in corresponding surfaces. ③Suggest two conditions to judge redundant nodes and delete them. ④Judge nodes according to Boolean computation in connective pointer and comparative position relation, and generate meshes. It uses iterative methods for solving the shortest way in Boolean Computation. Because it will take too much time to establish node connective relation in corresponding surfaces and solve the shortest way and make Boolean Computation. We suggest the second algorithm: ①Dispose nodes in interior and exterior shell surfaces with the mapping and interpolation's method according to topological relationship and geometric position. ②Allot relative number for every node according to the nodes' relative position and the topological relationship. ③Assemble all shells as a whole with the dynamic plan's method according to shells'relative topological and geometric relation. ④Generate hexahedral elements according to the nodes'three-dimension number. The FE technology is strong method to make structure analysis, in order to establish intimate relationship with CAD technology and enhance the FE software code's quality, it chooses the object oriented programming technique to develop a FE module. This module includes nine kinds of element, those elements can basically meet the demand of structure static analysis. In bridge structure, prestress component plays an important role. Prestress is converted normally into equivalent loads in the FE analysis. All present research papers about equivalent load of prestress aims at beam element,and reinforcing steel bar's linearis is straight line and circle line, which cannot cover all prestress bar's linearis. Aiming at concrete bridge's analysis with body element, this paper suggests a kind of mathematical computation method to compute equivalent load of prestress. As to curve bar: ①Compute equivalent loads of prestress converted to Gauss point with one-dimension Gauss integral. ②Get bar's Gauss coordinate point in natural coordinate system to body element. Computation course is concerned with solution for three times nonlinear equation group, solve it with Newton iterative algorithm. ③Allot stress in Gauss points to correlative nodes with the use of interpolation function in natural coordinate system. As to anchored end's load: ①Anchored end's load acts on one surface of element, view four nodes...
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