近断层脉冲型地震动下位移谱阻尼修正系数

Damping modification factors of displacement response spectrum under pulse-type motions in near-fault region

现行规范采用阻尼修正系数(DMF)调整阻尼比不同于5%时的弹性位移反应谱,然而未考虑到近断层脉冲型地震动的影响。选取了代表性前方向性脉冲记录,研究了矩震级、场地类别和距离对脉冲周期的影响,同时指出脉冲周期与相应伪速度谱峰值周期之间具有较好的线性相关性,然后以周期与脉冲周期比和阻尼比为双变量,采用Levenberg-Marquardt算法进行非线性回归分析,提出了能够较为准确反映数据点分布规律的DMF模型。结果表明,随着脉冲周期的减小,DMF峰值对应的周期越小,而在中长周期范围DMF越趋近于1.0;与现行规范相比,模型MDF强烈依赖于脉冲周期、结构振动周期和阻尼比,且当三者位于不同取值范围时,规范DMF过低或过高。

Damping modification factors （DMF） are spectrum with damping ratio different from 5%. However, the used in modern seismic codes to adjust elastic response codes have the disadvantage of neglecting impact of pulse-type motions. The influence of moment magnitude, site classes and distance on pulse periods was investigated here with representative forward-direction ground motion records with distinct velocity pulses. Furthermore~ Pulse periods were confirmed to possess better linear relationship with the periods corresponding to the peak values of pseudo-velocity spectrum. Fin@, Nonlinear regression analyses were conducted with Levenberg-Marquardt method. The resulting DMF model, as a function of both periods ratios and damping ratios, successfully represented data distribution. The results showed that with the decrease in pulse periods, the periods corresponding to DMF peak values reduce and DMF approaches 1.0 in middle and long period range ; in contrast to the considerations of current seismic codes, DMF model is strongly dependent on pulse periods, the periods of structural vibration and damping ratios, and in comparison with DMF proposed by the authors, DMFs of the current codes are too low or too high, depending on pulse periods, structural vibration periods, and damping ratios.