Research On The Dynamic Characteristic And Seismic Response Of Chinese High Pedestal Ancient Timber Buildings

Chinese ancient timber buildings are the outstanding representative of oriental ancient buildings, which are called a wonderful work in the architectural history of mankind. In this paper, one of the architectural forms that the high pedestal ancient timber buildings were studied. In order to study such buildings better, the Xi'an Drum-Tower was taken as an example in this paper. The corresponding finite element models about Xi'an Drum-Tower were established and through the numerical calculation to study the antiseismic performance of Drum-Tower. Through the finite element analysis of Xi'an Drum-Tower, the dynamic characteristics and the laws of seismic response for such buildings were obtained and also provided a method for analysis such buildings. That provided the theoretical basis and technical reference for protection, maintenance, reinforcement of such buildings.The distinction between the high pedestal ancient timber buildings and the general ancient timber buildings is the high pedestal. To understand this kind of architectural form better, the foundation of Chinese ancient timber buildings were described simply; the most primitive form of the high pedestal ancient timber buildings that is the high platform ancient buildings were described. On this basis, the three-dimensional finite element models of the high pedestal, the upper timber structure , the overall structure about Xi'an Drum-Tower were established by using the ANSYS finite element analysis software. The high pedestal included the high station and base. The horizontal spring element was used in the connecting form of the column bases and timber columns for realizing the sliding friction. The semi-rigid characteristic of mortise-tenon joint was considered. Dougong was considered as a damper and the approach of centralized quality was used for the heavy quality roof. The physical or mechanical parameters and spring stiffness values of the material in the models were adopted by the results of experiments. By modal analysis, the laws of dynamic characteristics were studied; the seismic waves were input to the upper timber structure and the overall structure for the time history analysis and the characteristics of seismic response were obtained. The laws of dynamic characteristics and seismic response were studied about the high pedestal influencing the the upper timber structure.By modal analysis, the frequencies of high pedestal are relatively dense; the difference in the adjacent frequencies is small and the frequencies is relatively stable. The natural frequencies of timber structure are in a fluctuation range and is easy to disperse; the frequencies are not very stable. Before the fourth natural frequency of the overall structure, the frequencies are closed to the frequencies of timber structure; the frequencies behind the fourth natural frequency of the overall structure are closed to the frequencies of high pedestal; the high pedestal mainly influences the high frequencies. The main vibration modes of high pedestal are the vibration of level and torsional; The main vibration modes of timber structure are the vibration of the slip of level and torsional; Before the fourth vibration modes of the overall structure, the vibration modes are mainly the vibration of timber structure; behind the fourth vibration modes of the overall structure, the timber structure is vibrated with the vibrating of the high pedestal and that changes the dynamic characteristics of the upper timber structure. So it must take the influence of the high pedestal into account when the high pedestal ancient timber buildings are analyzed.The results of time history analysis show that the displacement of the head of columns in the upper timber structure increases gradually with the increase of seismic excitation; the displacement of the head of columns in the overall structure are also increases gradually with the increase of seismic excitation; the displacement of the head of columns in the overall structure is growth of 20.478% or more that relative to the displacement of the head of columns in the upper timber structure. The dynamic coefficient of the timber structure is reduced with the increase of seismic excitation and the average dynamic coefficient is less than 0.779; The dynamic coefficient of the overall structure also have a decreasing trend, but the average dynamic coefficient is less than 1.386; The dynamic coefficient of the head of columns in the overall structure are 0.818 times more than the dynamic coefficient of the the head of columns in the timber structure. The high pedestal obviously amplifies the displacement and acceleration of the head of columns in the timber structure. It also shows that the head of columns are easy to damage and the high pedestal will directly affect the safety of the upper timber structure. That is detrimental for the seismic performance of the upper timber structure. Through the above analysis, the study of the buildings with high pedestal, in particular, to study the dynamic characteristics and seismic response analysis, which must consider the impact of the high pedestal and the high pedestal part must be considered in the calculation model.