| With the development of the economy and social construction,the bridges are also becoming more widely used,The pier serves as the main load-bearing and transmission component of the bridge,it willbear the self-weight of the bridge as well as suffer the potential threat of car crash,therefore,it is very meaningful to study the dynamic response of the pier under the imapct load and its collisionresistance measures.This paper was based on the cases of vehicle impact on piers,the metallic hollow sphere structures(MHSS)were utilized as the anti-collision device,the research focused on single MHS and MHSS,and the microstructure characteristics of single thin-walled MHS were obtained,and then probed effects of microporosity on the elasticity and yielding of thin-walled metallic hollow spheres,also discussed the deformation characteristics and faliure of single MHS under quasi-static and impact compression,meanwhile,the effects of microporosity on the deformation behaviors under both compression tests were probed.Afterwards,the mechanical responses of the MHSS under quasi-static and SHPB compressions were studied,and a reasonable explanation was given to the negative poisson ratio of the MHSS under compression.Finally,the vehicle impacted on the pier as the background,and the different thickness of the MHSS were used as the bridge pier protection device,using 1:10 scale model for impact tests,and the finite element software ABAQUS was used to simulate all the impact test conditions and made a comprehensive comparision with the tasts in the end.Based on the above,the detailed conclusions can be obtaioned as follows:1.Nanoindentation was used to probe the Young's modulus and hardness of the nonporous MHS wall material,and synchrotron X-ray computed tomography(XCT)conducted to obtain its porous microstructure and pore morphology.Three-dimensional finite element modeling was performed to obtain the mechanical response of microcubes with varying porosity trimmed from the XCT-derived real digital model of the porous MHS wall.Results show that both the Young's modulus and yield strength of the porous wall decrease nonlinearly with increasing porosity,and their relationships follow the same format of a power law function and agree well with prior experimental results.2.For the effect of the microporosity,when there exist weak regions on the local partitions of the single MHS thin wall,the weak regions will buckle first and generate"buckling lines" on the single MHS if they are adjacent,the buckling failures will occur along these "buckling lines" on the MHS under the quasi-static compression,among the "buckling lines" will generate some hinges which make contributions on load capacity during the densification process.3.At different impact velocities,the time of the bottom of MHS becoming sunken is different,also the increase in concave depth at the top and bottom of the shell is different,and the larger the impact velocity,the earlier the depression of the bottom shell is.The norminal stress-strain curves are nearly the same in the low impact velocity,while they are quite different in the high velocity.The distribution of microporosity can affect the deformation process of single MHS under impact,and the deformation process is almost the same with it is under quasi-static compression expect there exists large portions of weak regions like HDM.4.A simplified continuous model is established based on the three-dimensional Cosserat continuum theory,the formulae of poisson's ratio are given according to several regular packings of MHSS,it is concluded that the negative poisson ratio of the structureis determined by the ratio of the shear stiffness to the normal stiffness,when the tangential stiffness is greater than the normal stiffness,the negative poisson ratio phenomenon occurs.5.After the pier is crashed by the solid sphere,the acceleration of the impact point and the top point,strain increased amplitudes and top displacement are both decreasing with the increase of the thickness of the MHSS,it proves that the MHSS has an excellent energy absorption and it can protect the bridge pier effectively.6.Under the dynamic impact compression,the plateau stress of the MHSS is significantly greater than that of the quasi-static compression.with the increase of impact velocity,the plateau stress will increase.7.The concrete strain of concrete surface,displacement at the pier top and accelerations of the FEM models are consistent with practical pier models,while the peak values of the former are slightly higher than the latter,which declares that it is feasible to explore the dynamic responses of the pier under impact load with ABAQUS.For the perspective of the security of pier,the FEM simulation is conservative... |
PDF Full Text Request