水介质中冰-桥墩碰撞动力响应分析

Dynamic response analysis of ice-bridge pier collision in water medium

为准确模拟冰-桥墩碰撞过程中墩体结构的动力响应,基于流固耦合(fluid-solid interaction, FSI)的计算方法,运用ANSYS/LS-DYNA软件数值模拟了水介质中冰排与桥墩在不同碰撞影响参数下的动力响应。结果表明:恒定附加质量(constant added mass, CAM)模型相比FSI模型冰载荷计算结果偏大,是因为CAM模型忽略了降低冰排速度的“水垫效应”,但其计算效率高,计算时间是FSI模型的1/10,更有利于桥墩防撞设计,而FSI模型能够更真实地模拟冰-桥墩碰撞场景。综合分析该研究所模拟的不同冰排工况,发现桥墩在冰排撞击作用下呈现明显的冰激结构振动特征,桥墩侧向位移云图随着应力波的传递呈现明显的层状分布,其顶部侧向位移幅度最大,因此在工程设计时应充分考虑其对桥梁整体安全的影响;随着冰排速度、冰排厚度和冰排压缩强度的增大,冰载荷平均值均呈现近似多项式函数关系。此外,研究发现当冰排压缩强度小于2.668 MPa(环境温度高于-15℃)时,冰载荷平均值明显减小,表明环境温度的变化对于桥墩受冰排撞击挤压作用所受的冰害问题具有显著的差异。其仿真研究成果拟为桥梁及桥墩防撞设施设计提供参考。

Here,to correctly simulate dynamic response of pier body structure in process of ice-bridge pier collision,based on fluid-solid interaction(FSI)calculation method,the software ANSYS/LS-DYNA was used to numerically simulate dynamic responses of ice rafts and piers in water medium under different collision influence parameters.The results showed that the ice load calculation results with constant added mass(CAM)model are larger than those with FSI model,it is due to CAM model ignoring“water cushion effect”which reduces ice raft speed,but its calculation efficiency is high and its calculation time is 1/10 of FSI model’s to be more conducive to pier anti-collision design,while FSI model can more realistically simulate ice-pier collision process;after comprehensively analyzing simulation results under different ice raft working conditions,piers exhibit obvious ice-induced structural vibration characteristics under impact actions of ice rafts,pier lateral displacement cloud map has an obvious layered distribution with transmission of stress waves,and its top lateral displacement amplitude is the largest,so its effects on the overall safety of bridge should be fully considered in engineering design;with increase in ice raft speed,ice raft thickness and ice raft compression strength,average ice load has approximate polynomial function relations to them,respectively;when ice raft compression strength is less than 2.668 MPa under ambient temperature>-15℃,average ice load obviously decreases,so effects of variations of ambient temperature on ice damages of piers due to ice rafts impact and compression have significant differences;the simulation study results can provide a reference for designing anti-collision facilities of bridges and piers.