Study On Solid Modeling Technology In Bridge Three-Dimension CAD

With the rapid development of economic construction and transport services in our country, construction of highway is in good unprecedented opportunity, road and bridge construction has entered a peak period; the beginning of this century is the golden opportunity of railway construction, and is also period of rapid progress of high-speed railway bridge in our country. Since the 21st century, the bridges have been made their target on long span, high-strength and light-type structure. With the incessant increasing of the bridges span, load and design speed, it has more important realistic meaning to make more precise modeling of the bridges, and analyze the force they bear. In the process of bridge design, the contradiction between heavy design tasks and lack of design resources will become more prominent, the vigorous expansion of CAD technology is an important way to improve the design method, improve design efficiency and design quality.Now, Chinese bridge CAD technology is going ahead all over the world through decades of development and innovation. But now as far as bridge CAD technology is concerned, analysis program and drawing program is independent basically, which can take on main part design work, but it is necessary to finish other work through manual calculation and manual drawing. In the course of structure analysis, beam element is mainly used,though solid element are used, which is immature. It directly produces two-dimension plane working drawing at the aspect of drawing. Automatic graph system is poor interactive and the lack of correlation exist between the graphics.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.In bridge three-dimension CAD technology, solid model technology is strong tool of express bridge geometric shape. Solid model data can completely express data suck as bridge's geometric information and construction information. The research domain of using solid model technology to express accurate and integrated civil engineering data is blank. 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.Now there is a large software Salome with more than one functions can be used to model or modify kinds of bridge CAD models, and make meshing, analyze the force they bear and calculate how mach reinforcing steel they need. Salome do a very good performance for finite element analysis,but it do a poor performance for edit graphics and drawing graphics, in this text, object-oriented programming language (Python) as a tool is used during the secondary development of Salome, it is an opportunity to enhance the edit graphics capacity and the ability of solid modeling of Salome.The paper is divided into five parts, research and analysis are showed about CAD solid modeling of the bridge through combining theory and practice.In the first part it introduced the significance of study on bridge CAD technology and researched status at home and abroad, analyzed and summarized the lack of bridge CAD, described the main content in this paper.In the second part it introduced parametric drawing and geometric modeling, narrated the contents about parametric drawing, such as definition, condition, design steps, design technology and thought. Efficiency and correctness of the design will be improve if parametric design technology is introduced to the three-dimension solid modeling. It introduced the definition of geometric modeling, the express way of body, the basic coordinate system, topological structure of three-dimension geometry solid, the geometric information and topology information is a complete expression of solid, the express method of solid model and data structure.In the third part of the paper introduced the technical support of modeling: the superiority of Linux operating system; the application characteristics of object-oriented Python programming language; the function and the general structure of the platform about Salome, the function of geometry module.The forth part is the main body of the full text. The author will use scripting language (Python) to compile documents in the Linux operating system, and then import these documents into Salome, the model will be set up and showed in the display window when the procedure is totally right by detect and run (the system will be point these errors if there exist some errors). The detailed analysis and study about set up solid model of T-girder bridge box-girder bridge are introduced, axonometric drawing, and cross-sectional view and elevation view are on display.At the last part, through the analysis of the four parts above, the results of the research are summarized. It summarized that ideas and advantages of three-dimension geometry solid by use this method, this method makes up for defects of presently bridge CAD. Raised questions for further research through the prospects of develop this system.