西安永宁门箭楼结构及抗震性能分析

为获取中国木结构古建筑保护和修缮中的技术参考依据,以西安城墙永宁门箭楼为研究对象,采用SAP2000有限元软件中摩擦摆隔振单元模拟柱脚平摆浮搁式连接、橡胶隔振单元模拟斗栱层及虚拟弹簧单元模拟榫卯连接,建立了结构空间有限元模型,并进行动力分析。通过3个模型(柱脚刚接、铰接和平摆浮搁连接)的模态对比分析,发现平摆浮搁连接方式能够延长结构的周期,其中前三阶周期变化较明显,分别比柱脚刚接、铰接时延长了约72％和24％;通过反应谱和动力时程分析,得到各个层面的动力放大系数,结果表明,木结构古建筑的隔震性能主要体现在柱脚、梁柱榫卯连接和铺作层部位;耗能分析结果表明,输入的地震能量大部分被结构自身的振型阻尼(平均74.32％)和结构的连接(11.89％)所消耗。

Analysis of structural and seismic performance of Yongning Gate embrasured watchtower of Xi' an City Wall

To gain the technical basis for the protection and restoration of the ancient Chinese timber structures, the embrasured watchtower of Yongning Gate of Xi′an City Wall was studied and simulated by the Sap 2000 software. The friction isolation element was applied to simulate the float connection between column and plinth, and the rubber isolator element was applied to simulate tou-kung layer. In addition, the finite element model of the embrasured watchtower was established and consequently a dynamic analysis was carried out by applying the spring element to simulate the mortise-tenon connection. Through the modal contrast analysis to the three models (the rigid connection, hinge, float connection between column foot and plinth), the comparative results showed that the float connection mode could lengthen structures natural periods, and the first three periods were more obvious, which were longer about 72％ and 24％ compared to rigid connection and hinge of column foot separately. By the response spectrum and the dynamic response time history analyses to the timber structure model, the dynamic magnification factors of each layer were obtained, which showed that the vibration isolation performance of ancient Chinese timber structure mainly manifested in the column foot, tenon mortise connection as well as the p’u tso layer. The structural energy dissipation analysis results showed that the majority seismic energy was consumed by the modal damping (average 74.32％) and the tenon mortise connection (average 11.89％).