| Space grid is a sort of preferable roof type for long span buildings. It has many advantages, for example forces are transferred in a 3D manner, save steel material, large rigidity, small building highness, industrialized, beauty sculpt ect. There are tremendous buildings adopt space grid structure as roof domestic and abroad, including big gymnasium, airdrome, middle training house, exhibition hall, club , showplace, dinning hall and industry workshop. However, how to perform seismic design of space grids is still an important problem concerned, because disaster as earthquake happen very frequently in recent years.The rule of free vibration and vertical seismic action of pyrimid space grid(PSG) roof structures are studied in this paper.Part 1. Finite element theory, functions of ANSYS software and typical analysis process are introduce in this part. Principals of how to ensure geometry parameter of space grids finite element model are given and F90 program to calculate member force and chord section is developed according <> (SGDC code) so as to determine the real constant ANSYS needed. To create finite element model of PSGs, program to create node, element number and restriction information is compiled also. Comparison between <> method and ANSYS is carried out, and results show that the method to create PSG finite element model by ANSYS is correct and the simplified method given by <> to calculate chord force is of high accuracy in precision.Part 2. Equivalent sandwich plate and ANSYS modal analysis are used in the calculation of free vibration. The process of modal analysis and the subspace alternate theory are introduced. Comparison results show that as a simplified method equivalent sandwich plate method is accurate in precision. It also proved the study of free vibration property of space grids adopt ANSYS software is reliable. The dynamic property of PSG is studied through free vibration analysis. Through free vibration frequencies analysis of 44 PSGs, the general rule of PSGs is achieved and influence factors for PSGs are determined.Part 3. Vertical seismic action of PSG is studied in this part and calculation method of seismic action are introduced. The method of how to determine vertical seismic spectrum by horizontal seismic spectrum is introduced also in this part. Vertical seismic spectrum curve values are transformed so that it can be adopted by ANSYS spectrum analysis. The procedures of spectrum analysis are given. Through the seismic action analysis of PSGs on II ground, we achieve the distribution rule of seismic internal force coefficients. Part 4 . The inherent relationship between vertical seismic internal force coefficient max and the first vertical frequency is found by researching seismicinternal force coefficients of 15 kinds of PSGs, then practical calculation methods for pyramid space grids is determined, and testifying is also carried out.
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