A Method Based On Modal Analysis For The Conceptual Design Research Of Long-span Spatial Structures

The structure concept design is an overall structure scheme design conducted from a macroscopic and comprehensive perspective. Though there are some corresponding stipulations in structural design code aimed at structure concept design, they are mainly qualitative regulations. In the process of guiding structure design, they tend to be conservative and poor operation in practice. To some complex structures, design experience still plays the dominant role.Modal analysis is a kind of quantitative analysis method. It is mainly applied to the research of structural dynamic issues present. However, Structure characteristic parameters are parameters which only have reference to the structure’s mass and stiffness. So they should play more important role in wider structure field, especially in the design and analysis that related with structure’s mass and stiffness. Modal analysis method generally does not consider load combinations and not involve complicated mechanical analysis. So the modal analysis method is more suitable for guiding structure concept design.Subsidized by the National Natural Science Fund Project "A Research of Designing Method of the Structural Engineering Controlled by Characteristic Parameters"(Grant No.50978232), the stiffness characteristics and mode features of the long-span spatial structures are analyzed and summarized combined a movie theater. Then concept design method of this kind structure is studied, expecting to provide a method or idea for the stiffness design of long-span spatial structures. Meanwhile, it is also expected that this kind of method can applied to the concept design of other kind of structures.The main work of this paper is as follows:1) The stiffness characteristics and mode features of the long-span spatial structures are analyzed and summarized via three groups of models. Corresponding relations between the stiffness distributions and the mode of the long-span spatial structures are studied, expecting to use the mode features to guide the stiffness design of the long-span spatial structures. 2) A movie theater is made use of as an example of the long-span spatial structures. From the analysis, the defects of the movie theater in the structure stiffness design can be easily found out utilizing the mode analysis.3) The original revised plan, strengthened by sticking steel plate, of the movie theater is discussed and mode analysis of the original reinforcement scheme is conducted. Then conclusions that it cannot effectively improve the local stiffness of the movie theater are obtained. And then, a new kind of revised plan-revised by steel space frame is put forward. It is proved by the mode analysis conclusions that the modal response of the new kind of revised plan is good. It can solve the problem of local insufficient stiffness of the movie theater. It is proved that mode analysis method is a kind of structure concept design method that should be popularized.From the above analysis, it shows that modal analysis can continuation to the field of non-structural dynamic. And it is an effective method worth promoting in large-span spatial structure concept design, especially in stiffness design.