Static Elasto-plastic Analysis Of Long-Span Rigid Spatial Structures Under Vertical Earthquake

The long-span structures are one of the most rapidly developing types of structures. It is widely used in large-scale and public buildings. Its seismic characteristics are widely concerned by the researchers. Because of the rapid development of seismic resistance researches on the long-span spatial structures, different computation methods for seismic analysis have been correspondingly used in different types of structures to predict the structural response accurately. For example, the static elasto-plastic analysis method, named Push-over method, is widely adopted in the seismic analysis of the regular tall-buildings. Whereas the fundamental vibration mode of the long-span spatial structures is vertical deformation, the Push-over method does not suit for the long-span spatial structures any more. In other ways, the great deal of time consumption makes it difficult to apply the time-history method to calculate the response and evaluate the seismic resistance of the long-span spatial structures. Therefore, a new vertical static elasto-plastic analysis method and a new seismic resistance performance evaluation method are proposed for the seismic analysis of the long-span rigid spatial structures in this paper.Based on the reading and analysis of a lot of research references and reports, response spectrum method, pseudo-dynamic method, time-history method and static elasto-plastic analysis method are compared and summarized. The research work in this thesis is listed.According to the recent researches on characteristics of the vertical earthquake, the vertical seismic response spectrum is established in the dissertation. The response spectrum can be transformed into design response spectrum. Furthermore, the long-span rigid spatial structures can be analyzed with the method of design response spectrum. The relationship between the vertical shear force of the supporting joints excited by earthquake and the displacement of the control points of the structure can be transformed into the traditional relationship between the acceleration spectrum and the displacement spectrum (elastic response spectrum). Considering the ductility coefficient, the elastic response spectrum can be transformed into elasto-plastic response spectrum.Based on the principle of push-over method adopted in FEMA273 (Federal Emergency Management Agency) and ATC-40(Applied Technology Council) for seismic resistance analysis of the tall-buildings, a new static elasto-plastic analysis method for long-span spatial structures, named "Push-down method" is proposed in this thesis, including the fundamental principle, calculating target displacement and the failure criterion. At the same time, the fundamental mode pattern of vertical load (FMPL) and the multi-mode pattern of vertical load (MMPL) used in Push-down method are established. The basic principles of these two methods and transformation formulas of vertical capacity spectrum and improved capacity spectrum are derived. Considering ductility coefficient, the vertical elastic demand spectrum and vertical elasto-plastic demand spectrum are also derived.Through modal analysis, the dynamic characters of the long-span spatial structures can be obtained, such as mode participation coefficient, mode mass coefficient. The applicability scope of the Push-down method in long-span rigid spatial structure is given.To illustrate, a simple numerical example of a beam grid floor analyzed by FMPL is presented. The vertical seismic resistance evaluation of this floor is obtained. Comparing the results of Push-down analysis with the time-history analysis, It is found that the Push-down method is much more convenient to evaluate the seismic resistance performances of the long-span spatial structures, in which the fundamental mode is mainly vertical deformation mode.Another simple numerical example of a single-layer reticulated shell structures analyzed by MMPL is presented. Through mode combination method, the response of seismic resistance of the long-span spatial structure under multi-mode pattern of vertical loads can be obtained. Also, the results of Push-down analysis are compared with the results of the time-history analysis. Considering the multi-mode effects, the results of two methods go close.In a word, the Push-down method can be easily applied to evaluate the seismic performance of the long-span rigid spatial structures, of which the vibration mode is mainly vertical deformation. Considering the combination effect of multi-mode pattern of vertical load, the results are accurate enough.