考虑高台基影响的西安安定门城楼动力特性及地震响应分析

Analysis on dynamic characteristics and seismic response of the Anding Gate Tower in Xi’an considering high stylobate

为了准确评估西安安定门城楼的结构特性及抗震性能,采用原位动力特性测试与有限元数值模拟相结合的方法,对城楼进行考虑及不考虑高台基(瓮城东城墙)影响的动力特性及地震响应分析。首先对城楼上部木结构进行原位动力特性测试,获得其自振频率和振型;然后分别建立城楼上部木结构、高台基及整体结构(高台基+木结构)的三维有限元模型,采用模态分析方法获得了各计算模型的自振频率和振型,将上部木结构自振频率和振型的模拟结果与原位测试结果进行对比以验证模型的正确性,并进行上部木结构计算模型与整体结构计算模型动力特性的对比分析;最后分别对上部木结构和整体结构模型输入不同幅值的El Centro波、Taft波及兰州人工波三种地震激励,将两种计算模型的动力响应进行对比。结果表明:高台基对城楼5阶以上的高阶频率和结构振型影响较大,并使上部木结构的位移响应、层间位移角、加速度响应及楼层剪力均有较大程度的增大,对结构的抗震性能产生不利影响。

In order to accurately evaluate the structural characteristics and seismic performance of the Anding Gate Tower in Xi’an, a combination method of in-site dynamic characteristics test and finite element simulation was used with and without considering the influence of high stylobate(east wall of Wengcheng). Firstly, the in-site dynamic characteristics test of the upper timber structure of the gate tower was carried out. The natural frequencies and vibration modes were obtained. Then, the three-dimensional finite element models of the upper timber structure, the high stylobate and the whole structure(high stylobate and timber structure) were established, respectively. The natural frequencies and vibration modes were obtained by modal analysis. The numerical results of the natural frequencies and vibration modes of the upper timber structure were compared with the in-site test results to verify the accuracy of the models. Additionally, the comparative analysis of the simulated dynamic characteristics between the upper timber structure and the whole structure model was carried out. Finally, three kinds of seismic excitations including El Centro wave, Taft wave and Lanzhou wave with different amplitudes were input to the models of the upper timber structure and the whole structure respectively. The dynamic responses of the two models were compared. The results show that, for the fifth-order and higher frequencies and vibration modes, the high stylobate increases the displacement response, the interlayer displacement rotation, the acceleration response and the story shear of the upper timber structure to a large extent, which is unfavorable for the seismic performance of the timber structure.