Seismic Response Analysis of High-Pier Bridge under Near-Fault Multiple Pulse Record Excitation
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摘要: 为了研究近断层地震的多脉冲效应对不规则高墩大跨桥梁非线性地震响应的影响，首先，采用眼观识别的方法选取了典型的多脉冲、单脉冲和非脉冲3组地震动；然后，采用小波变换识别方法和能量识别方法对其脉冲性进行识别，研究了脉冲地震动识别方法对多脉冲地震动的适用性；最后，以某大跨度高墩桥梁为例，基于OpenSees建立了其非线性有限元模型，对其进行了非线性地震响应分析，对比研究了近断层多脉冲地震动及单脉冲地震动对不规则高墩桥梁非线性地震响应的影响. 研究结果表明：现有的近断层脉冲识别方法只适用于速度时程中只含有一个主脉冲的地震动，对于多脉冲地震动，其失效的可能性非常大；近断层脉冲地震动对不规则高墩桥梁具有更强的破坏性，特别是在多脉冲地震作用下，1号、2号两个高墩的墩顶位移需求分别增加了118.9%和109.6%，墩底弯矩和墩底曲率也有明显的增大；近场多脉冲地震作用下主梁的碰撞次数增大了3～5倍，碰撞力也会增大2～3倍，主梁更容易发生严重的碰撞破坏，在抗震设计时应采取适当防撞措施.Abstract: The multiple pulse effect of near-fault seismic records on the nonlinear seismic response of high pier railway bridges (HPRB) was investigated. First, three representative groups of seismic records, namely, single pulse record (SPR), multiple pulse record (MPR) and none pulse record (NPR) were selected by visual inspection. Second, pulse characteristics were quantitatively identified using wavelet analysis method (WAM) and energy-based approach (EBA) to investigate if impulse ground motion identification method was applicable to MPR. Finally, a typical HPRB, located in the southern region of China, was adopted as the research object, the non-linear finite element model was established in OpenSees platform, and the non-linear seismic response analysis of the HPRB was carried out. The effects of MPR and SPR on the nonlinear seismic response of the HPRB were compared. The results obtained from the analyses indicate that the WAM and EBA are applicable to ground motions with only one dominant pulse in the velocity history, and are not applicable to multiple pulse ground motions. Near-fault MPRs and SPRs pose the risk of stronger damage to irregular high pier bridges than NPRs. Under MPR excitation, the top displacement of pier 1 and pier 2 is, respectively, 118.9% and 109.6% larger than under NPR excitation. The bending moment and the curvature at the bottom of the pier also increase. Near-fault MPR is found to produce pounding force and pounding times that are, respectively, 3−5 times and 2−3 times greater than those by NPR excitation. In the near field multiple pulse earthquake, the main beam is more likely to cause severe impact damage, and thus, the appropriate anti-collision measures should be adopted in seismic design.
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图 10 碰撞响应与速度脉冲的对应关系
Figure 10. Relationship between pounding response and velocity pulse
表 1 3类地震动详细信息
Table 1. Detail of selected three type ground motions
地震动类型 地震记录 Rrup/km PGA/（× g） SF Tp/s PI Ep 多脉冲 TCU059-NS 17.11 0.165 2.542 7.3 0.218 1 0.300 TCU104-NS 12.87 0.089 4.737 6.9 0.826 5 0.379 TCU107-EW 15.99 0.130 3.232 7.4 0.129 7 0.236 TCU107-NS 15.99 0.147 2.862 5.6 0.000 4 0.091 单脉冲 TCU031-EW 30.17 0.115 3.656 6.2 1.000 0 0.557 TCU036-EW 19.83 0.137 3.071 5.8 0.999 9 0.562 TCU040-EW 22.06 0.162 2.592 5.6 1.000 0 0.621 TCU049-EW 3.76 0.279 1.507 8.8 0.999 8 0.596 非脉冲 CHY074-EW 6.20 0.322 1.303 0.044 9 0.237 TCU079-NS 10.97 0.424 0.990 0.003 4 0.172 TCU070-EW 19.00 0.254 1.654 0.162 0 0.049 TCU076-NS 2.74 0.428 0.980 0.102 8 0.194 
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表 2 Hertz-Damp模型特征参数
Table 2. Properties of Hertz-Damp model
特征参数 取值 初始间隙gp/mm 100 屈服位移δy/mm 1.6 初始刚度K1/（kN•mm–1） 8 472 应变硬化刚度K1/（kN•mm–1） 2 916 等效刚度Keff/（kN•mm–1） 3 472 最大入侵位移δm/mm 16
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表 3 桥梁动力特性
Table 3. Dynamic characteristics of the selected bridge
振型阶数 周期/s 频率/Hz 质量参与系数/% 纵桥向 横桥向 第 1 阶 1.323 0.756 61.15 0 第 2 阶 1.278 0.783 0 40.92 第 3 阶 0.953 1.049 6.33 0 第 4 阶 0.902 1.108 0 0.56 第 5 阶 0.696 1.436 0.11 0 第 6 阶 0.688 1.454 0 15.65
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表 4 近断层脉冲效应对桥墩地震响应的放大系数
Table 4. Amplification factor of near-fault impulse effect on seismic response of pier
墩号 单一脉冲 多脉冲 曲率放大
系数位移放大
系数弯矩放大
系数剪力放大
系数曲率放大
系数放大系数
位移弯矩放大
系数剪力放大
系数1号 1.221 1.103 1.043 1.029 3.707 2.189 1.053 1.385 2号 1.926 1.085 1.019 0.983 8.924 2.096 1.119 1.543 3号 0.864 0.852 0.866 0.918 1.193 1.211 1.192 1.181
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表 5 近断层脉冲效应对主梁碰撞响应的影响
Table 5. Details of maximum pounding force and average pounding frequency
脉冲类型 梁-台碰撞 梁-梁碰撞 梁-台碰撞 碰撞力/(× 107 N) 碰撞次数/次 碰撞力/(× 108 N) 碰撞次数/次 碰撞力/(× 108 N) 碰撞次数/次 多脉冲 29.70 32.50 3.67 23.00 32.50 27.75 单脉冲 8.73 9.95 1.41 9.00 8.56 7.25 非脉冲 9.67 5.50 1.15 5.25 10.60 5.00
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