汶川地震近断层地震动作用下结构地震响应特征分析

Analysis of the seismic response characteristics of building structures subjected to near-fault ground motions from Wenchuan earthquake

研究了具有不同自振特性的建筑结构在近断层速度脉冲型及非速度脉冲型地震动作用下的结构层间变形分布,揭示了近断层速度脉冲对工程结构地震响应的特殊影响.从汶川MS8.0地震近断层强震记录中选取两组典型速度脉冲型记录和非脉冲型记录,根据确定的目标地震动强度水平,利用时域叠加小波函数法对选择的强震记录进行调整,使之与目标地震动水平对应的加速度反应谱保持一致,以此作为结构地震反应分析的地震动输入.选取具有不同自振特征的3层、11层和20层典型钢筋混凝土框架结构,建立有限元分析模型,分别计算在速度脉冲型与非速度脉冲型记录作用下这些结构层间变形分布.研究表明,速度脉冲型记录与非速度脉冲型记录作用下结构层间变形有明显差异,且与结构自振特征有关.就低层结构的层间变形而言,非速度脉冲型记录的影响较速度脉冲型记录的影响大.随着结构自振周期的增加,高阶振型的影响更加明显.与非速度脉冲型记录相比,速度脉冲型记录的结构层间位移反应中值及离散程度较大.速度脉冲型记录更容易激发高层结构的高阶振型,产生较大的层间位移反应.非速度脉冲型记录对中低层结构层间变形影响较大.因此,在开展近断层结构地震影响评价时,应考虑近断层速度脉冲的影响.

This paper focuses on studying the effects of near-fault ground veloci- ty pulses on building structures. Inter-story drift distributions of structures subjected to velocity pulse-type records and non-pulse-type records were investi- gated to reveal the effects of near-fault strong motions on building structures with different natural vibration periods. Two groups of typical velocity pulse re- cords and non-pulse records were selected from Wenchuan MsS. 0 earthquake, and a wavelet method of time domain synthesizing was used to modify the se- lected records, matching the target spectra from determined seismic intensity. The modified ground motions were used as the basic strong motion data for seis- mic response analysis. Finite models of 3, 11 and 20-story RC frame structures were established, and inter-story drift distributions of these three buildings sub- jected to typical velocity pulse-type records and non-pulse-type records were in- vestigated. The study reveals that the inter-story drift distributions are quite different when the structures are subjected to pulse-type records and non-pulse- type records for the 3, 11 and 20-story RC frame structures, and are correlated with the natural vibration properties of building structures. In terms of low-rise buildings, inter-story drifts are larger for non-pulse-type records than those for pulse-type records. The influences of high modes on inter-story drifts become much more obvious with the increase of story number. The median value and dispersion of inter-story drifts are much larger when subjected to pulse-type re- cords compared with non-pulse-type records for high-rise buildings. Pulse-type records tend to induce higher modes response, resulting in large inter-story drifts for high-rise buildings. Non-pulse-type records have relatively large effects on inter-story drifts primarily in the fundamental mode for low-rise buildings. It can be concluded that the effects of near-fault velocity pulses should be taken into consideration when assessing seismic damage potential for near-fault building structures.