Abstract:Taihe Palace is located in the front part of the Forbidden City, Beijing, China, and is composed of foundations, a wooden frame, tou-kung (bracket sets), a roof (hip type), and filler walls. The beams and columns of the building are connected by a tenon-mortise joints. Taihe Palace represents the apotheosis of Chinese ancient timber buildings. Its foundation bed is composed of a stylobate and high platform. To effectively protect Chinese ancient timber buildings, Taihe Palace is taken as an example to study the influence of its foundation bed on the seismic performance of its superstructure. Based on its constituent characteristics such as the foundation bed, free-standing column root, tenon-mortise connection between beam and column, and bracket sets (tou-kung) on the column tops, two finite element models of the building, with and without the foundation bed, were built. Using modal analysis, the influence of the foundation bed on the natural vibration characteristics of the upper structure was studied. Using response spectrum analysis under an 8-degree intensity of frequently occurring earthquakes, the influences on the distribution of internal force and deformation of the upper structure were discussed. Using time history analysis under an 8-degree intensity of seldom-occurring earthquakes, the influences on the acceleration and displacement response of the upper structure were analyzed. Results show that when the foundation bed is considered as part of the whole structure, the basic frequency of the structure decreases and the participation coefficients of its main modes increase. Compared with the structure without a foundation bed, under the 8-degree intensity of frequently occurring earthquakes, the principle tension and compression stresses in the timber part increase separately; in the filler wall, the principle tension and compression stresses decrease and its deformation increases. The main reason is that the foundation bed itself participates in the vibration, which decreases the stiffness of the whole structure. In addition, the peak stress values of the foundation bed are all with permissible limits. Under the 8-degree intensity of seldom-occurring earthquakes, although its vertical response slightly decreases, its acceleration and displacement in the horizontal direction obviously increase. Thus, it is necessary to consider the dynamic magnification effects of the foundation bed on the upper structure of Taihe Palace.