列车运行引起高架桥群桩基础地面振动分析

采用半解析数值方法分析列车运行引起高架桥群桩基础地面振动,研究合理设计桩基减小地面振动。半解析数值模型包括列车–轨道模型、高架桥模型、群桩模型。列车轨道模型中采用多质点弹簧–阻尼模型模拟列车,采用美国功率谱描述轨道随机不平顺,使用Euler梁模拟钢轨,采用Hertzian非线性公式描述轮轨接触,采用振型分解法求解轮轨作用力。铁路高架桥采用弹性支座简支梁模拟,采用传递系数矩阵和群桩影响因子分析桥墩下群桩的动力阻抗,根据桥墩的动力平衡方程求得桥墩–地基相互作用力,采用Green函数求得弹性半空间地面振动。研究铁路高架桥下群桩参数对地面振动的影响,分析不同桩长、桩直径、桩间距和轨道不平顺条件下地面振动速度1/3倍频程的大小。结果表明:轨道不平顺对桥墩作用力有较大影响,对小于6 Hz的地面振动影响较小,对大于6 Hz的地面振动影响较大。合适调整桥梁跨度与车速组合可减小地面振动。车速小于260 km/h时,桩径对地面振动影响较小;车速大于260 km/h时,增加桩径可减小地面振动。适当增加桩间距可避开振动增大区、减小地面振动随车速的增加。合理设计桩长可减小地面振动的增大区域。

Ground vibration induced by moving train on viaduct with group pile foundation

The semi-analytic method is adopted to analyze the influence of ground vibration due to train moving on viaduct supported by group piles to explore ways of reducing ground vibration. The semi-analytic numerical models include train-rail model, viaduct model and group pile model. The train is simulated by a multiple-mass spring-damping model. The America power spectrum is used to model the rail irregularities. The rail is modeled by Eular beam and the wheel-rail contact Hertzian non-linear formula is used. The wheel-rail force is solved by modal analysis method. The railway viaduct is modeled by elastically supported beam, and the impedance of group piles is analyzed by transfer coefficient matrix and interaction factors. The bridge pier-ground interaction force is solved by dynamic equilibrium equations and the ground vibration on half space is solved by Green function. The influence of the parameters of group piles on ground vibration is discussed. The results show that the rail irregularities have a great influence on pier force. The ground vibration greater than 6 Hz is influenced by the rail irregularities while the vibration less than 6 Hz is little affected. The ground vibration can be mitigated by combined bridge span and train speed. When the train speed is less than 260 km/h, the influence of pile diameter on ground vibration is limited; while it is greater than 260 km/h, increasing pile diameter can reduce the ground vibration. Increasing the pile spacing has two advantages of keeping away from the vibration increasing area and reducing the ground vibration as the increase of train speed. The increasing area of ground vibration can be reduced by the rational design of pile length.