考虑桩土作用的桥墩车撞动力响应分析

Dynamic responses of bridge pier subjected to vehicle collision considering pile-soil interaction

桥墩受车辆撞击,可能发生强烈的动力响应,甚至产生破坏,对桥梁结构及行车安全造成很大威胁。为了更精确地分析桥墩受车辆撞击的动力响应,为桥梁防撞设计提供理论依据,比较分析是否考虑桩土作用所得计算结果的差异,从而探究考虑桩土作用对计算结果的影响。以郑州四环线某桥为背景,通过LS-DYNA软件基于有限域土体法、等效嵌固法、等效弹簧法建立桩土作用模型并建立墩底固结模型,分析桥墩受车辆撞击的动力响应及损伤特征。在分析中,选用福特F800(8 t)轻型货车作为碰撞车辆,设置3种车辆行驶速度为初始碰撞速度,并假设车辆沿横桥向正面撞击桥墩。计算结果显示:应用墩底固结模型和桩土模型计算桥墩受车辆撞击的动力响应,由前者得到的撞击力和横桥向墩顶位移偏小,而撞击力持时偏大;采用3倍、5倍和8倍桩径法所得横桥向墩顶位移依次增大,但撞击力峰值依次减小;由3倍桩径法、弹簧法和有限域法所得横桥向墩顶位移差异不大,由后两者与8倍桩径法所得撞击力峰值的差异较小。研究结果表明:考虑桩土作用与否对分析结果有明显影响,撞击力峰值主要是在车辆发动机与桥墩碰撞时产生;桩基边界约束条件对计算的撞击力峰值影响显著,在等效嵌固法中增大桥墩刚度会使墩顶位移减小,而墩底固结模型使墩顶位移最小;采用各桩土模型,其损伤机理与损伤部位相似,即桥墩受撞击部位主要发生冲剪破坏;桥梁各构件的连接处也往往会出现较大应力,是易损部位。

Impacted by vehicle,the bridge pier may occur strong dynamic responses and even damage,which poses a great threat to the bridge structure and vehicle running safety.In order to more accurately analyze the dynamic responses of bridge pier when it is impacted by vehicle and provide theoretical basis for bridge collision prevention design,the differences between the results calculated whether or not considering pile-soil action were compared,so as to explore the influences of pile-soil action on the results calculated.A bridge of Zhengzhou Fourth Ring Road was taken as the background.Pile-soil models based on finite domain soil method,equivalent embedding method and equivalent spring method were established by LS-DYNA software.Besides the pier-bottom-consolidation model was also established.The dynamic responses and damage characteristics of bridge pier impacted by vehicle were analyzed.During the analysis,Ford F800(8 t)light truck was selected as the collision vehicle.Three vehicle speeds were set as the initial collision speed,and it is assumed that the vehicle impacts the front of the pier from the direction transverse to bridge longitudinal direction.The calculation results are as follows.When calculating the dynamic responses of the bridge pier by using the pier-bottom-consolidation model and the pile-soil model,the impact forces and lateral displacements at pier top obtained from the former are smaller than those from latter.The lasting time from former is longer than that from latter.The lateral displacements at pier top obtained by 3 times,5 times and 8 times pile diameter method increase in sequence,but the peak value of the impact force decrease in in sequence.There is not big difference among the lateral displacements at pier top obtained from 3 times pile diameter method,spring method and finite field method.There is only a little difference among the peak impact forces obtained from spring method,finite field method and 8 times pile diameter method.It has significant influence on the analysis results whether or not consider the pile-soil action,and the peak value of impact force mainly occurs when the vehicle engine collides with the bridge pier.The boundary constraints on pile foundation have significant effect on the peak value of impact force calculated.For the equivalent embedding method,increasing the pier stiffness will reduce the pier top displacement,while using the pier-bottom-consolidation model will lead to the pier top displacement to be smallest.The damage mechanism and position for all pile-soil models are similar.The pier is mainly damaged by shear at the position impacted.The great stress also usually occurs at the joints of bridge components that they are vulnerable to damage.