残损明清古建筑木结构动力特性研究

Study on dynamic characteristics of a damaged ancient timber structure of Ming-Qing Dynasty

古建筑木结构在历经几百年的服役后存在不同程度的残损,显著降低了结构的受力性能。为研究残损古建筑木结构的动力特性,选取北京故宫内具有明清古建筑特征的井亭木结构为研究对象。通过现场检测,确定结构的残损类型并分析残损原因,同时,采用环境激励法进行现场动力测试,获得结构的前3阶自振频率和振型。基于实测结果并考虑材料老化、立柱倾斜和柱脚糟朽等损伤因素,分别建立结构的完好和残损有限元模型,对其进行模态分析和地震响应计算。研究结果表明：由于重屋顶和关键节点的半刚性构造特征,木结构的自振频率相对较低;材料、构件和节点的残损降低结构刚度和自振频率;在地震动作用下,残损结构的柱脚水平反力小于完好模型,而其加速度和位移响应明显大于完好结构。

Ancient timber buildings have experienced different degrees of damage after hundreds of years of service, which significantly reduces their structural performance. In order to study the dynamic characteristics of damaged ancient timber structures, a pavilion timber structure in the Imperial Palace with typical structural characteristics of Ming Dynasty and Qing Dynasty is considered. Through field inspection, structural damage types were determined and the reasons behind the damage were analyzed. Furthermore, the first 3 natural frequencies and modal shapes of the structure were obtained by field dynamic testing using an environmental excitation method. Based on the field measured result and considering the damaged factors including material aging, column inclination and decay of column foot, both finite-element models of undamaged and damaged structures were established, and modal analysis and seismic response calculation were conducted. The analyzed results show that because of the heavy roof and the semi-rigid feature of the key joints, the natural frequency of the timber structure is relatively low. The damage of the materials, components and joints reduces the structural stiffness and natural frequency. When under the action of earthquake, the horizontal reaction force of the column foot of the damaged structure is smaller than that of undamaged structure, while the acceleration and displacement responses of the damaged structure are significantly greater than those of the undamaged structure.