海域地震动水平加速度反应谱阻尼修正系数

为估算不同阻尼比海域工程结构的反应谱,研究了海域工程反应谱的阻尼修正系数(D_MF)模型。基于S-net台网的5 680条海底水平向地震动记录,分析了矩震级、断层深度和震源类别等震源参数,以及震源距和沉积层厚度对D_MF的影响,提出了考虑阻尼比和谱周期的海域地震动水平加速度反应谱D_MF模型,并与陆域模型进行了对比。研究表明:矩震级和震源距对D_MF影响显著,低阻尼D_MF随矩震级和震源距增大而增加,高阻尼D_MF随之增大而降低,而D_MF受断层深度和沉积层厚度的影响不显著；与陆域研究不同,在低阻尼中长周期时海域地震动的浅地壳和上地幔地震的D_MF略大；谱周期大于0.1 s时和小于0.1 s时,可分别用三次和二次对数多项式模拟阻尼比对D_MF的影响,谱周期的影响可分别用四次和三次多项式表示；海域D_MF模型与陆域模型差异显著,海域D_MF模型更能合理预测不同阻尼比的海域地震动反应谱,提出的海域地震动反应谱D_MF模型为海域工程多阻尼抗震设计谱的确定提供了参考。

Damping modification factor for horizontal acceleration spectrum from offshore ground motion

For estimating the response spectrum of offshore engineering structures with different damping ratios, the damping modification factor (D_MF) model of offshore engineering response spectrum was studied. Based on 5 680 horizontal offshore ground motion records from S-net network, we analyzed the effects of source parameters such as moment magnitude, fault depth, and earthquake type, as well as source distance and sediment thickness on D_MF, and proposed a D_MF model for horizontal acceleration spectrum from offshore ground motions considering damping ratio and spectral period, which was compared with onshore models. Results show that moment magnitude and source distance had significant impact on D_MF. D_MF with low damping ratios increased with the increase in moment magnitude and source distance, while D_MF with high damping ratios decreased with the increase in moment magnitude and source distance, and D_MF was not sensitive to the influence of fault depth and sediment thickness. Compared with the study of onshore area, the D_MF values of shallow crustal and upper-matle earthquakes in this study were slightly larger under low damping ratios and medium-long periods. When spectral periods were greater than 0.1 s or less than 0.1 s, the influence of damping ratio on D_MF could be simulated by cubic or quadratic logarithmic polynomials, and the influence of spectral period could be expressed by quartic or cubic polynomials. There were significant differences between offshore D_MF model and onshore models. The D_MF model for response spectrum from offshore ground motions proposed in this paper provides reference for the determination of seismic design spectrum of offshore engineering under various damping ratios.