重型车辆撞击下桥墩碰撞力简化模型

Simplified impact force model of pier under heavy vehicle collision

为了探究钢筋混凝土桥墩在重型车辆撞击下的安全性能,建立了重型车辆-桥墩碰撞精细有限元模型,研究了撞击速度、桥墩直径、上部结构边界条件和货物高度对桥墩破坏模式和内力分布的影响;分析了不同工况下的车辆碰撞力特征,并基于车辆初始动能耗散特点提出了碰撞力简化模型。分析结果表明:重型车辆碰撞过程可以分为保险杠、发动机和货物撞击桥墩3个阶段,碰撞力在前2个阶段主要集中在0.9m高度处,而在第3个阶段主要分布在2.7m高度处;在重型车辆撞击下,不仅桥墩端部会出现严重损伤,碰撞部位附近也可能发生严重的局部冲剪破坏;由于忽略了碰撞荷载的动力效应和车辆与桥墩的耦合作用,采用《公路桥涵设计通用规范》(JTG D60—2015)中建议的等效静力设计方法难以获得桥墩的实际撞击响应;撞击速度对桥墩内力和碰撞力的影响最显著,货物高度的不同会改变碰撞力的空间分布,但不会影响桥墩的最大内力响应;重型车辆的初始动能存在6.5MJ的阈值,当初始动能小于该阈值时,车辆发动机和保险杠的碰撞作用对桥墩动力响应起主导作用,反之,后部货物的碰撞作用控制碰撞力峰值;碰撞力简化模型和精细车辆模型预测所得桥墩最大内力响应的相对误差在8%以内,且计算耗时从6~7h缩短到4min。

To explore the safety of reinforced concrete piers under heavy vehicle collision, a refined finite element(FE)model of heavy vehicle-pier collision was established.The effects of impact velocity,pier diameter,superstructure boundary condition and cargo height on the failure mode and internal force distribution of pier were investigated.The characteristics of vehicle impact force under different conditions were analyzed,and a simplified impact force model was proposed based on the dissipation characteristics of vehicle initial kinetic energy.Analysis result shows that the heavy vehicle collision process can be divided into three stages such as the bumper,engine and cargo collide the pier.The impact force is mainly concentrated at the elevation of 0.9min the first two collision stages,and is distributed at the elevation of 2.7min the third collision stage.Under the heavy vehicle collision,not only will there be serious damage at the end of pier,but also there may be serious local punching shear damage near the collision site.Due to the neglection to the dynamic effect of impact load and the coupling effect of vehicle and pier,the equivalent static design approach recommended by the General Code for Design of Highway Bridges and Culverts (JTG D60-2015)is difficult to obtain an actual impact response of pier.The impact velocity has the most significant influence on the internal force and impact force of pier.The difference of cargo height changes the spatial distribution of impact force,but will not affect the maximum internal force response of pier.A threshold of 6.5MJ exists in the initial kinetic energy of heavy vehicle.When the initial kinetic energy is less than the threshold, the impact actions from the vehicle engine and bumper play dominant roles in the dynamic response of pier.On the contrary,the impact action of cargo at the back determines the peak impact force.The relative error of the predicted maximum internal force responses of pier between the simplified impact force model and the refined vehicle model is less than 8%,and the computation time shortens from 6-7hto 4min.1tab,20figs,31refs.