Seismic Performance Of 800 Meters Span Reticulated Mega Structures

The progress of the technology and scientific innovations as well as the growing needs of the human society have paved the way for the construction of larger spanned structures.The super large spanned reticulated mega structures are key subject of this research.While few studies have been conducted on the static and stability research of such structures,little has been done on the evaluation of the seismic performance.Earthquakes are inevitable and pose a serious threat to the safety of the human lives and properties.Detailed research is required for the seismic performance evaluation of the structures under frequent earthquakes,which is covered in this thesis.The research involves two configurations of the super large span reticulated structures of 800 m span.The Kiewitt type and the Geodesic type structures are considered and the influence of the support system on the Geodesic type structure is also investigated.The research was mainly centered on the following aspects.1)The dynamic characteristics of the structures including the natural vibration properties were analyzed.The damping characteristics of the structures were computed considering multi-mode references using the least square method.Three different actual ground motion records were selected after screening which comply with the selection criterion defined in the seismic code.A system for data extraction and handling was developed and the displacement and the internal force response of the structures under the selected ground motions were analyzed.The applied earthquake direction had influence on its orthogonal direction displacements.The horizontal earthquake played the controlling role in the seismic response of the structure.The static and dynamic displacement responses under the three groups of selected ground motion were similar.The magnification factor of the displacements of major control points of the structures were 1.16,1.07 and 1.24 for the Kiewitt,Geodesic Type I and Type II structures respectively.The magnification factor of the dynamic stress was under 1.2 for all types of structure.The responses were similar for different earthquake intensities and were within reasonable limits for 9 degrees earthquake.2)The influence of the support system was analyzed in the Geodesic structure.The support system was found to have an immense contribution in the vertical stiffness of the structure,with the support Type I showing localized massive displacements and stresses.Of the studied structural models,Geodesic Type was found to have the best seismic performance.3)The results of the time history method were compared with the results obtained from the modal decomposition response spectrum method.The response spectrum method can be used within reasonable error limit for the Kiewitt models,but the error limit in the Geodesic models was higher.4)The influence of the substructure on the seismic performance of the structure was studied.The results showed that the presence of the substructure improved the overall stiffness of the structure.The magnification factor of the displacement under the earthquake for control points was not more than 1.28 and for the internal stresses it was not more than 1.25.