近断层地震动空间分布特征对斜拉桥地震响应影响

为研究近断层地震动空间分布特征对斜拉桥地震响应的影响规律，以台湾集集地震近断层地震动为研究对象，根据台站与断层的空间相对位置，将近场波分为破裂前方区域(Forward District，FD)、破裂区域(Middle District，MD)和破裂后方区域(Backward District，BD)三类波，对其进行频谱分析表明，MD区域和FD区域地震动低频成分显著而BD区域高频成分显著。以某主跨为406m的斜拉桥为依托工程，对三个区域地震动作用下地震响应规律进行对比研究，计算结果表明三个区域地震响应规律和量值均有显著差异，不同区域结构动力响应与地震动特征参数相关程度迥异。MD区域塔顶纵向位移较BD区域增加3.03倍，塔底弯矩和剪力增加1.0倍；FD区域塔顶纵向位移较BD区域增加1.06倍，塔底弯矩和剪力较BD区域却分别下降了35.5%和32.2%。基于上述结果，建议对于位于破裂区域的结构进行抗震设计时，须同时提高强度与变形需求，采用PGV及PGA作为结构动力响应参数的评估指标，还应选择合理地震动方向；对于破裂前方区域，结构动力响应受输入能和PGA影响显著，须重点控制结构的变形；对于破裂后方区域，应着重提高结构的强度需求，首选断层距及PGV作为地震动输入的控制参数。

Influence of spatial distribution characteristics of near-fault ground motions on seismic responses of cable-stayed bridges

In order to investigate the influence of spatial distribution characteristic of near-fault ground motions on the seismicresponse of a cable-stayed bridge, Chi-Chi(Taiwan) Earthquake records distributed in Forward District (FD), Middle District (MD) andBackward District (BD), which are divided based on the position of the sites of the district relative to the fault rupture, are selectedas seismic input. The response spectrum analysis shows that the seismic ground motions in MD and FD district contain abundant low-frequency component, while the spectral values in BD are generally significant in the short period range. The seismic responses of a406m-span cable-stayed bridge are analyzed with above seismic ground motions as input. The calculation results show that the bridgeunder MD earthquakes has the maximum seismic responses, the displacements at the top of the tower and internal forces at the base of thetower are 4.03 and 2.0 times than those under BD records, respectively. The average value of longitudinal displacement under FDearthquakes is 2.06 times that under BD earthquakes, while the average value of moment and shear force decreases 35.5% and 32.2%,respectively. It is also revealed that different parameters of near-fault ground motions have various correlations with the dynamicresponses of cable-stayed bridge in 3 districts. Numerical results illustrate that the seismic design of structures in MD should takeinto account higher strength and deformation demand. The parameters, such as PGV and PGA value, can be selected as intensity indices toevaluate the dynamic seismic responses of structures, and seismic ground motions in the reasonable direction should be selected. Theinput energy and PGA have significant influence on the dynamic seismic responses of structures in FD, so structural deformation shouldbe restricted in the area. For the structures in BD, strength demand should be highlighted,and fault distance and PGV can beselected as preferable evaluation parameters of the near-fault ground motions.