传统楼阁式木塔抗震性能研究

Study on the seismic performance of a traditional pavilion-style pagoda

考虑七度多遇至八度罕遇烈度水平,对一个缩尺比例为1/5的七层传统楼阁式木塔模型进行了模拟地震振动台试验。运用模态分析和系统识别理论,辨识了各水准地震作用后模型结构X向和Y向前四阶振型、频率和阻尼比。试验发现七度罕遇和八度罕遇水准地震作用下模型部分栌斗和散斗出现横纹劈裂裂缝,但模型结构未发现局部构件明显损坏或整体倒塌。模态识别结果表明模型结构X向和Y向一阶阻尼比均大于10%,其余模态阻尼均大于5%;震后结构X向一阶频率下降了17%,一阶模态阻尼比增加到16%。研究可为传统木结构抗震研究提供试验支撑。

This paper presented the preliminary test results of a shake table test on a 1/5 scaled Chinese traditional seven-story pavilion-style wooden pagoda. The test considered three types of earthquake waves and a seismic intensity ranging from the frequently-met 7 degree to rarely-met 8 degree as specified in Chinese seismic design code. Modal analysis and system identification were carried out to identify the mode shapes,natural frequencies and modal damping ratios of the first four modes. It was found that the model structure remained structurally sound with no structural collapse or member failure,while minor perpendicular-to-grain tensile splitting was observed in certain cap blocks and distributed blocks of the Dougong connections( also known as complex brackets). The results also indicated that the first modal damping ratio of the principal directions of the model was more than 10%,while those of the other modes were found to be more than 5%. After the exposure to the earthquake excitations,the decrease of the natural frequency and the increase of the damping ratio corresponding to the first mode of the model structure were found to be 17% and 16%,respectively.The generated knowledge can be used as reference for design and retrofitting of traditional timber structures.