Research On Dynamic Responses Of Large-span Space Structures Subjected To Wind And Earthquake

Large-span spatial structures have been applied widely in many fields, with new forms and systems frequently developed by civil engineers. Till now, great acheivements have been made on static analysis of these structures, including branches such as mechanic solution, design optimization and displacement trace, etc. However, dynamic response solution is still a difficult problem, for the reliability and accuracy are not necessarily ensured. To light-weight, low-stiffness large-span sturctures, dynamic responses could be a dominant consideration in design process, thus, enough emphasis should be laid on dynamic problems such as wind or earthquake induced vibrations.In the paper, thorough review and research are put on solution of wind and earthquake induced responses for large-span spatial structures, in which some key parameters, e.g. superpostioned vibration mode number, are elaborated or specified. Furthermore, practical calculation methods for wind and earthquake induced vibration are also suggested. Related research is performed via programming on VC++ platform, and these programs are incorporated into MSTCAD structural design software.The paper summarizes methods to describe fluctuatitive wind pressure, and adopts random vibration theory in the calculation of wind-induced responses within frequency domain. Gust loading factors are defined in terms of displacements and internal forces, and "consistant loading factor" are proposed for a whole structure. Strain energy is calculated to reflect mode contribution to wind-induced vibration, on which basis, a proper number of mode-superposition order is suggested. After large-scale parametric analysis, practical formulae for gust loading factors of two typical large-span structures are proposed.The paper also put emphasis on mode superpostion response spectrum (MSRS) method for seismic response of large-span structures. "Modal attendance mass" and "modal participation factor" are defined and deduced, and further used for determination of proper mode-superposition order. A new "virtual vibration mode method" is proposed in case of unknown high order modeshape accounting for a large percentage in seismic response.Last but not least, the paper takes a serious review of time-history dynamic response calculation for large-span spatial structures. Implicit and explicit intergration scheme are studied and compared, while linear and nonlinear solution methods are both elaborated. A time-history dynamic solution program module is developed, using Newmark/Wilson-θ implicit intergration scheme. Based on that, calculations are performed to practical structures, and comparisons are made between time-history solution and MSRS results. The results show that MSRS results are not necessarily larger than that of time-history solution, hence, the latter method cannot be neglected in analysis and design of large-span structures.