近断层竖向地震动下双层桥梁排架墩抗震性能分析

Analysis on Seismic Behavior of Double-Deck Bridge Bents under Near Fault Vertical Earthquake Ground Motions

为研究近断层竖向地震动对钢筋混凝土(Reinforced Concrete,RC)双层桥梁排架墩地震反应的影响,以某双层高架桥设计资料为依据,建立其抗震数值分析模型.选取40组近断层地震动记录,对模型分别输入水平单向地震动和水平向+竖向地震动,对比分析了双层排架墩在两种加载方式下地震反应.结果表明:与水平单向地震动下的反应相比,在水平向+竖向地震动作用下,排架墩的反应显著增大.顶层桥墩层间最大位移角、残余位移角分别增大了85%和80%;顶层桥墩墩底截面纵筋最大应变、曲率延性系数分别增大了87%和70%.底层桥墩层间最大位移角、残余位移角分别增大了40%和26%;底层桥墩墩底截面纵筋最大应变、曲率延性系数分别增大了33%和18%.考虑竖向地震动时,底层及顶层桥墩均可能轴向受拉,而水平单向地震动下桥墩均处于受压状态.近断层水平向+竖向地震动作用下RC双层桥梁排架墩的损伤破坏远大于仅考虑水平向地震动时的损伤破坏.

To study the influence of vertical near fault earthquake ground motions on the seismic response of reinforced concrete(RC)double-deck bridge bents,a seismic analysis model for this type of bents was built based on the design details of one double deck viaduct.Forty groups of near fault earthquake ground motions were selected and used for dynamic time history analysis of the bents.The response of the bents under horizontal motions only,under combined horizontal and vertical ground motions were analyzed and compared with each other.The results show that:Compared with the response under horizontal motions only,the response of the bent under combined horizontal and vertical ground motions increased obviously.For the upper floor piers,the maximum and residual drift ratios increased by 85%and 80%,respectively.The maximum longitudinal bar strain and the curvature ductility factor of the bottom section of the upper floor piers increased by 87%and 70%,respectively.As for the down floor piers,the maximum and residual drift ratios increased by 40%and 26%,respectively.And the maximum longitudinal bar strain and the curvature ductility factor of the bottom section of the down floor piers increased by 33%and 18%,respectively.Under combined horizontal and vertical motions,both the upper and down floor piers may suffer axial tensile load,while all the piers suffer axial compression load only under horizontal motions.The RC double-deck bridge bents would suffer more severe damage under near fault combined horizontal and vertical ground motions compared with that under horizontal ground motions only.