太和殿基座对上部结构抗震性能影响分析

Influence of the Taihe Palace Foundation Bed on the Seismic Performance of Its Superstructure

故宫太和殿是中国古建筑的典型代表,其基座由台基和高台组成。为有效保护古建筑,采用数值模拟方法,以故宫太和殿为例,研究古建基座对上部结构抗震性能影响。基于太和殿基座、浮搁柱底、榫卯连接、斗拱等构造特征,建立两种有限元模型:不考虑基座/考虑基座。通过模态分析,研究基座对太和殿上部结构自振特性的影响;通过Ⅷ度常遇地震作用下的谱分析,研究基座对太和殿上部结构内力、变形分布及峰值的影响;通过Ⅷ度罕遇地震作用下的时程响应分析,研究基座对太和殿上部结构加速度和位移响应的影响。结果表明:考虑基座后,太和殿结构基频减小,主振型参与系数增大;Ⅷ度常遇地震作用下,太和殿结构木构架的变形及主应力峰值略有放大,墙体所受内力减小;Ⅷ度罕遇地震作用下,太和殿典型部位的木构架加速度、位移响应有不同程度放大。因此基座对太和殿上部结构动力放大作用不可忽略。

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.