The Mechanism Research Of Reinforced Concrete Piers Subjected To Vehicle Collisons

According to the statistic analysis,the vehicle collision has been one of the important causes that lead to the bridge damage worldwide.The traffic on the highway and urban bridges is so large,and the traffic environment is so complex that the threat of vehicle collision is particularly evident.As the main vertical components of the bridge,the piers once damaged or destructed in the vehicle collision accident,would possibly lead to the collapse of the bridge,resulting in serious loss of life and property.The reinforced concrete(RC)bridge piers are commonly used for the highway and urban bridges.There are important engineering value and theoretical significance to study the impact of RC bridge piers from vehicle collision.In this paper,the model test,numerical simulation analysis and theoretical model are used to study the impact mechanisms of RC bridge piers.The main innovative works would be presented as follows:(1)Considering the influence of the axial force and the crush of the vehicle's nose,the model test of the single-column RC bridge piers under vehicle collision is carried out.The bridge pier models and the buffers are designed,the buffer consisting of eight steel tubes is used to simulate the crushing behavior of the vehicle nose,the dynamic response and deformation or damage mode of the RC column with axial force under the elastic impact and damage impact are obtained by adopting horizontal impact test methods.The repeated impact tests of damaged RC columns are carried out for the first time,the study shows that the impact response and the deformation or damage mode of damaged RC columns under repeated impact are basically the same with the intact specimens;the RC column with small bending damage still has the better anti-collision ability under repeated impact.(2)The dynamic response and the main influencing factors of RC column with axial force under the lateral soft impact are systematically studied.The failure mechanism and energy dissipation mechanism are revealed,and the identification method of failure mode is proposed.a)The bending failure and shear failure tend to be the two main failure modes of the RC column with axial force under the lateral soft impact;the RC column designed for bending failure under static loads may be transformed into the shear failure under impact loads,the inertia effect and strain rate effect are the main reasons for the alternation of failure mode.b)The yield of tensile reinforcement and compressive failure of concrete in the plastic hinge region are the important symbols of bending failure of RC columns with axial force,the failure process can be divided into quasi elastic,cracking stage,yield stage and failure stage;the bending failure mechanism under impact loads are basically the same with that of the static load conditions,both of which are the tensile reinforcements yield before the compressive failure of the concrete in compression region;the dynamic bending bearing capacity is higher than the static bending bearing capacity,and the maximum bending moment at the bottom of RC column can be used as the evaluation indexes of dynamic bending bearing capacity;the stirrup ratio has little effects on the dynamic response of the RC column,and the peak value of the impact force and dynamic bending bearing capacity increase with the increase of the longitudinal reinforcement ratio and the axial force.c)The shear failure process of RC column with axial force can be divided into plastic hinge forming stage,crack development stage,stirrup yield stage and failure stage;the extension of diagonal crack and the fracture of stirrups after the formation of the plastic hinge at the bottom of RC column are the shear failure mechanism under impact loads;the dynamic shear bearing capacity is sharply and highly improved compared with that under the condition of static loads,the maximum shear force at impact point can be used as the evaluation indexes of the dynamic shear bearing capacity of RC column.d)The deformation energy of striker is the main energy dissipation mechanism of RC column under the lateral soft impact.For the bending failure mode,the strain energy of tensile reinforcement and compressive concrete in the plastic hinge region is the main energy dissipation mechanisms of RC column;the energy absorption capacity of RC column under shear failure mode is limited.e)Based on the numerical simulation results and the rigid-perfectly plastic model,the calculation method of impact resistance of RC column is put forward,the failure mode identification method of RC column under impact loads is proposed,and the calculation results are in good agreement with the experimental and numerical simulation results.(3)The study on the double-column RC piers subjected to truck impact is conducted via employing the numerical simulation and theoretical analysis method,the failure characteristics of the truck and the dynamic response of the double-column RC piers are analyzed,the model of impact force and elastic response of bridge piers are established respectively,the effects of the soil shear wave speed,the axial load,the pile diameter and the pile length are investigated.a)The crush process of the truck is progressive,of which the deformation stiffness is much smaller than the RC column;the RC column can be simplified to be the rigid column in the analysis of impact force;the pier damage occurs mainly on the truck-bridge contact area,the backside of impact point and the joints of the tie beam,the joints of the tie beam should be strengthened;the effects of impact direction on impact force is very small,but the deformation of bridge piers under longitudinal impact is significantly greater than that under the transverse impact.b)Based on the assumption of rigid column and considering the structural characteristics of the truck,the double degree-of-freedom model of impact force is established.By comparing with the numerical simulation results,it is showed that this model can better reflect the main characteristics of the impact force.c)Based on the Euler-Bernoulli beam theory and the Winkler foundation model,the elastic response model of bridge piers that has considered the influences of soil around piles,the axial force and the adjacent pier column is established.By comparing with the experimental results,it is showed that this model can better reflect the elastic impact response of bridge piers.The numerical examples are provided to show that the soil shear wave velocity and diameter of pile have important influence on the dynamic elastic response,while the influence of the pile length and the axial force is relatively small.