Analysis of Seismic Response of Bridge across Earthquake Fault with Different Input Modes of Seismic Action
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摘要: 大地震在近断层场地产生强烈地震动的同时,还会由于断层错动直接导致基岩甚至上覆土层破裂,在断层两侧产生显著差异性永久位移,造成位于断层附近或跨越断层的工程结构破坏。因此,跨断层桥梁面对的地震作用是断层两侧桥墩处场地的不同地震动,包括存在永久性位移的地震动。本文以垂直跨越走滑断层的多跨简支梁桥为例,基于OpenSees有限元模拟平台建立了桥梁结构的三维计算模型,计算分析了不同地震作用输入模式下桥梁结构的地震反应及其差异。考虑的地震作用模式包括:(1)断层两侧场地的地震作用视为相同的无永久位移的地震动,即无永久位移的一致地震动作用模式;(2)断层主动盘一侧场地的地震作用具有永久位移地震动,被动盘一侧采用无永久位移地震动,即具有永久位移的非一致地震动作用模式;(3)在断层主动盘一侧场地以静力方式施加断层错动位移,而被动盘一侧场地固定不动,即断层错动位移静力作用模式。计算结果分析表明,不考虑永久位移的一致地震动作用模式的地震动输入会导致严重低估桥梁反应计算结果,这也说明地震动的断层两侧永久性位移差异会显著增大桥梁结构反应;而一致地震动作用叠加断层错动永久位移静力作用的结果与非一致地震动作用模式的结果非常接近。为此,在某种程度上说,跨断层桥梁结构地震反应可采用一致地震动作用叠加断层错动位移静力作用的桥梁结构反应来近似模拟。Abstract: A large earthquake can produce strong ground motion at the near-fault site, and at the same time, it may directly break up the bedrock and even the overlying soil layers due to fault rupture, which leads to significant differential permanent displacement on both sides of the fault, and results in severe damage of the structure located near or crossing fault. Therefore, the seismic action on the bridge across fault is different on both sides of the fault, including the ground motion with permanent displacement. A simply supported girder bridge vertically across strike-slip fault is taken as an example, and a three-dimensional fnite-element model is developed using the earthquake engineering simulation software framework OpenSees (Open System for Earthquake Engineering Simulation). The seismic response of the bridge structure under different modes of seismic action is analyzed. The modes of seismic action considered include: (1) Seismic action of sites on both sides of the fault is regarded as the same ground motion without permanent displacement, that is, a consistent ground motion mode of seismic action without permanent displacement; (2) Seismic action of sites is regarded as a ground motion with permanent displacement on the active side of the fault, and a ground motion without permanent displacement on the passive side of the fault, that is, a non-consistent ground motion mode of seismic action with permanent displacement; (3) Fault dislocation displacement is applied to the site on the active side of fault, while the site on the passive side is fixed, that is, a static force mode of seismic action with fault dislocation displacement. The analysis results show that a consistent ground motion mode of seismic action without permanent displacement leads to a significant underestimation of the bridge structure responses, which indicates that the difference of permanent displacements of ground motions on both sides of the fault significantly increases the bridge structure response; The result from the superposition of the consistent ground motion mode and static force mode of fault dislocation permanent displacement is very close to the result from the non-consistent ground motion mode. Therefore, to a certain extent, the seismic response of cross-fault bridge structures can be approximately simulated by combining a consistent ground motion mode and a static force mode of fault dislocation displacement.
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表 1 原始地震动时程信息
Table 1. Original ground motion parameters
方向 PGA /g PGV/(cm·s−1) PGD/cm 横桥向 0.73 133.33 113.87 顺桥向 0.79 28.09 25.52 表 2 合成的地震动时程信息
Table 2. Synthetic ground motion parameters
类别 PGA /g PGV /(cm·s−1) PGD /cm 横桥向不考虑永久位移 0.60 111.97 105.39 横桥向考虑永久位移 0.60 117.79 138.88 顺桥向不考虑永久位移 0.60 118.89 110.84 表 3 横桥向P3和P4墩顶相对位移最大值和残余值
Table 3. Maximum and residual relative displacement of the pier top at P3 and P4 in the transverse direction
工况 最大值/cm
(残余值/cm)P2 P3 P4 P5 P6 1 9.0580
(−0.1654)4.6155
(−0.0405)3.8598
(−0.0254)6.4269
(−0.1254)5.5834
(−0.1095)2 9.8470
(0.2830)4.4210
(−1.2270)4.1927
(1.1377)6.3951
(−0.0789)5.5772
(−0.0757)3 9.2286
(0.1558)4.7349
(−1.4285)4.7175
(1.2923)6.4440
(−0.1007)5.5611
(−0.1431)表 4 横桥向P3和P4墩底剪力最大值和残余值
Table 4. The maximum and residual shear force at the bottom of pier P3 and P4 in the transverse direction
工况 剪力最大值/kN 残余剪力/kN P3 P4 P3 P4 1 7.9340$ \times {10}^{3} $ 7.6760$ \times {10}^{3} $ 0.0044$ \times {10}^{3} $ −0.0084$ \times {10}^{3} $ 2 7.6930$ \times {10}^{3} $ 8.1211$ \times {10}^{3} $ 1.7479$ \times {10}^{3} $ −1.7280$ \times {10}^{3} $ 3 8.5876$ \times {10}^{3} $ 8.9535$ \times {10}^{3} $ 1.9306$ \times {10}^{3} $ −1.9704$ \times {10}^{3} $ 表 5 横桥向P3和P4墩底弯矩最大值和残余值
Table 5. The maximum and residual bending moment at the bottom of pier P3 and P4 in the transverse direction
工况 弯矩最大值 /(kN∙m) 残余弯矩 /(kN∙m) P3 P4 P3 P4 1 1.7790$ \times {10}^{5} $ 1.6317$ \times {10}^{5} $ 0.0016$ \times {10}^{4} $ 0.0328$ \times {10}^{4} $ 2 1.6921$ \times {10}^{5} $ 1.7596$ \times {10}^{5} $ 4.7504$ \times {10}^{4} $ 4.6370$ \times {10}^{4} $ 3 1.7830$ \times {10}^{5} $ 1.9733$ \times {10}^{5} $ 5.2868$ \times {10}^{4} $ 5.2781$ \times {10}^{4} $ 表 6 P3和P4墩底扭矩最大值和残余值
Table 6. The maximum and residual torque at the bottom of pier P3 and P4 in the transverse direction
工况 扭矩最大值 /(kN∙m) 残余扭矩 /(kN∙m) P3 P4 P3 P4 1 5.4362$ \times {10}^{4} $ 0.6780$ \times {10}^{4} $ 0.0225$ \times {10}^{4} $ 0.0054$ \times {10}^{4} $ 2 5.3635$ \times {10}^{4} $ 2.2612$ \times {10}^{4} $ 2.0436$ \times {10}^{4} $ 2.0624$ \times {10}^{4} $ 3 5.2122$ \times {10}^{4} $ 1.8589$ \times {10}^{4} $ 1.7523$ \times {10}^{4} $ 1.7337$ \times {10}^{4} $ -
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