Research On Seismic Performance And Design Method Of High Pedestal Archaizing Steel Structure Buildings

The high pedestal ancient buildings are one of the outstanding representative in Chinese ancient buildings system. Up to the present, the seismic characteristics research work of the traditional high pedestal ancient buildings supported by wood frame for its upper structure is well-documented topic in the literature, and have a long research history. While the study for the same shape and the upper steel frame of the modern antique building structure and its seismic performance has been lacking. Due to the excellent seismic performance and properties of suitable for the green construction industrialization, the application of high pedestal archaizing steel structure in the antique building has been generalized gradually. Therefore, it is of great significance for ancient buildings protection and utilization with the study on the high pedestal ancient building steel frame structure and seismic performance.With the background of the Yongning Gate of Xi’an City wall embrasured watchtower rehabilitation project, choosing the steel framework as a loading bearing system for the embrasured watchtower. Two modeling methods of the complex ancient slope roof steel structure were firstly described and comparatively analyzed in details.Then the three-dimensional numerical model of the high pedestal ancient steel structure was established by using the ANSYS finite element analysis software. Furthermore, the dynamic characteristics of antique building structure and deformation characteristics and dynamic response of the structure influenced by the high pedestal were summarized.Based on the analysis of the results of the study, the reasonable simplified designed method of this type antique building is put forward in the end. And the main researchworks and results are as follows:Using ANSYS software, the element finite model of the wall high pedestal of the lower part of the watchtower and the steel frame and the whole structure were established respectively. By analyzing and comparing the corresponding dynamic modal results, it can be found that lower high pedestal changed the vibration regularity of the upper structure, especially with a significant influence on the high order frequency of the structure. The first ten order natural frequencies of the whole structure were between1.3707 Hz and 2.9033 Hz. The main frequency range of the general ground motion covers frequency region of the main mode of the whole structure. Which demonstrates that it is essential to develop the overall dynamic analysis of the lower part of the high pedestal and the upper steel frame structure.The El centro wave, Taft wave and Lanzhou wave were inputted upper part of the archaizing steel structure and overall structure respectively. Displacement and acceleration response of the upper steel frame column node of the top floor were analyzed and conducted its frequency spectrum analysis in the meantime. The results indicate that the displacement and acceleration response amplitude of top column of whole structure was increased, the acceleration average dynamic factor of top column is1.97 times of upper structure, which show that the high pedestal changes the magnitude and distribution of the acceleration Fourier spectrum. By inputting motion to high pedestal and doing history analysis, it can be concluded that acceleration amplitude of the node at the top of pedestal is increased, which indicates that the high pedestal have effect on amplification of filtering of ground motion. The acceleration Fourier spectrum of the platform top surface nodes shows that the frequency spectrum component similar to pedestal self of the frequency composition is amplified.Through suppling the upper structure and the whole structure’s time-history analysis and comparing structure’s maximum displacement on the top of column, the floor displacement, interstory drift and story shear force are all amplified when they are calculated by a whole structure model.Using the method of response spectrum, the results of earthquake force, floor displacement are conservative, Thus, it is necessary to add time-history analysis and envelope design when make the seismic analysis with ANSYS program in design work.We propose a solution: seismic force amplification coefficient method to make the seismic analysis for the building with the similar bottom structure of high pedestal in practical engineering, the upper archaizing architecture under the action of earthquake.Assume that the upper structure is fixed on rigid foundation when analyze its seismic response and we calculate the shear force of each floor according to the magnification factors confirmed by ANSYS program.