基于振动台测试及数值模拟的长周期设计谱评估

Evaluation of long-period seismic spectrum based on numerical simulation and shaking-table test of assembly structures

采用分层装配式多高层建筑结构缩尺模型的振动台试验以及足尺数值结构的地震反应分析,评估抗震设计谱长周期段的合理性和可靠性。以模型结构的实测振动周期和顶点加速度时程响应作为精度验证依据,构建并扩展模拟结构;剔除楼层加速度动力放大系数复合反应中二阶以上振型的分量,建立结构第一阶振型顶点和等效单自由度体系高度处的加速度动力放大系数谱以评估抗震设计谱。结果表明：基于SRSS规则求出的第一阶振型相对于楼层加速度动力放大系数的比例系数在建议设计谱的长周期段随自振周期增大而衰减,而规范设计谱对应的比例系数衰减趋势出现异常;建议设计谱的动力放大系数与第一阶振型的动力放大系数吻合较好,且谱值基本大于第一阶振型的动力放大系数谱值;规范设计谱的动力放大系数在速度敏感周期前段出现小于第一阶振型动力放大系数的情况,这表明有必要适当增大场地特征周期。建议设计谱估算的楼层加速度谱大于由规范设计谱以及基于试验与数值分析确定的楼层加速度谱,表明建议设计谱安全、可靠,且能体现长周期结构的高阶振型反应。

The shaking-table experiment data of small-scale muki-story and high-rise structural models assembled floor by floor and the numerical analysis data of seismic response of the full-scale structures were employed to evaluate the reliability and rationality of seismic design spectrum for long-period structures. Based on the experimental modal periods and the roof acceleration time history response of structural models, numerical simulation structures were modeled, validated and extended. Excluding the high-order modal components from combined floor acceleration, the dynamic amplification factor（DAF） of the first-order mode at the roof and the equivalent height of single-degree-of- freedom were established accordingly, and used to assess the long-period segment of seismic design spectrum in Chinese code and the proposed design spectrum. The results show that the proportional factor（PF） of the DAF of the first-order mode to the DAF of the floor acceleration, which is based on the SRSS method, increases with the period in the long-period segment of proposed design spectrum, while the PF corresponding to the long-period segment of seismic design spectrum in Chinese code has an abnormal attenuation trend. The DAF of proposed design spectrum has a good agreement with the DAF of the first-order mode, and greater values than those of the DAF of the first-order mode. The DAF of code design spectrum are smaller than the DAF of the first-order mode in the front section of velocity sensitive segment. It is necessary to properly increase the site characteristic period. The floor acceleration spectrum estimated by the proposed design spectrum is greater than that of code design spectrum and that of the experiment and analysis data. Therefore, it is safe for seismic design to use order mode of the long-period structures.