长周期抗震设计反应谱衰减指数与阻尼修正系数研究

对基于地震惯性力的绝对加速度谱和基于滞回恢复力的拟加速度谱进行差异解析，分析了长周期地震动拟加速度谱的衰减指数及其阻尼修正系数谱的变化规律。筛选长周期分量丰富的破坏性浅源强震数字化记录，通过弹性反应谱分析研究拟加速度动力放大系数谱的特征周期、两个下降段的衰减指数以及阻尼修正系数。分析结果表明：基于结构承载力的抗震设计谱应以基于滞回恢复力的拟加速度谱进行标定，以基于惯性力的绝对加速度谱标定对大阻尼比长周期结构的抗震设计偏于保守。拟加速度谱与绝对加速度谱在长周期段的衰减规律不同，大阻尼比长周期段拟加速度谱衰减速度较快。阻尼比0.05的标准抗震设计谱在第一和第二下降段采用形式简单的1/T和1/T²的规律衰减是合理可行的，无需通过修正衰减指数获得基于拟加速度的大阻尼比抗震设计谱。长周期地震反应谱的动力放大系数有显著的场地效应，以Ⅱ类场地为参考，Ⅰ~Ⅳ类场地效应系数分别取0.9、1.0、1.1和1.2较合适。地震动长周期分量对结构阻尼修正系数有很大的影响，基于拟加速度谱与绝对加速度谱的阻尼修正系数在长周期段有显著的差异。结构算例验证了长周期结构建议设计谱的衰减指数与阻尼修正系数取值的合理性。

Attenuation power index and damping reduction factor of seismicdesign spectrum for long-period ground motions

The difference between absolute-acceleration response spectrum (ARS) based on the earthquake inertia force and quasi-acceleration response spectrum (QRS) based on the hysteretic restoring force of the structure were explained, and the variation rule of the attenuation power index and the damping reduction factor of the QRS for long-period ground motions were studied. The digital ground motion records with rich long-period components from destructive shallow earthquake were selected, and the elastic response spectrum analysis method was employed to calculate the characteristic period, the attenuation power indexes of curvilinear decrease sections and the damping reduction factor of the dynamic amplification factor spectrum based on the QRS. The results show that the seismic design spectrum based on the bearing capacity should suitably be calibrated by the QRS based on the hysteretic restoring force of the structure, and the design spectrum calibrated by the ARS based on the earthquake inertia force might lead to rather conservative seismic design for the long-period structures with high damping ratio. The attenuation trend of curvilinear long-period section of the ARS is different from that of the QRS which attenuates comparatively fast for the structures with high damping ratio. It is rational and feasible for the standard seismic design spectrum based on the QRS with 5% damping ratio to adopt the simple attenuation rule in the first and second decrease section, namely 1/T and 1/T ² , respectively, and also the QRS with high damping ratio can be obtained and does not need to reduce the attenuation power index. The dynamic amplification factor of the long-period seismic response spectrum has significant site effects, and it is well suitable for the site class Ⅰ, site class Ⅱ, site class Ⅲ and site class Ⅳ to use 0.9, 1.0, 1.1 and 1.2, respectively, serving as the site effect factors and referring to the site class Ⅱ level. The long-period components of ground motions have a great influence on the damping reduction factors, and the damping reduction factors based on the QRS are significantly different from the damping reduction factors based on the ARS in the long-period section. Numerical engineering example validates the rationality of attenuation power index and damping reduction factor of the proposed design spectrum for long-period structures. 